[settings] Explicitly separate the concept of a completed fetched setting

The fetch_setting() family of functions may currently modify the
definition of the specified setting (e.g. to add missing type
information).  Clean up this interface by requiring callers to provide
an explicit buffer to contain the completed definition of the fetched
setting, if required.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

37 files changed, 610 insertions, 563 deletions

diff --git a/src/arch/i386/interface/vmware/guestinfo.c b/src/arch/i386/interface/vmware/guestinfo.c
index aa10fc01..a0530c8d 100644
--- a/src/arch/i386/interface/vmware/guestinfo.c
+++ b/src/arch/i386/interface/vmware/guestinfo.c
@@ -51,7 +51,7 @@ static int guestinfo_channel;
  */
 static int guestinfo_fetch_type ( struct settings *settings,
 				  struct setting *setting,
-				  struct setting_type *type,
+				  const struct setting_type *type,
 				  void *data, size_t len, int *found ) {
 	const char *parent_name = settings->parent->name;
 	char command[ 24 /* "info-get guestinfo.ipxe." */ +
diff --git a/src/arch/x86/core/cpuid_settings.c b/src/arch/x86/core/cpuid_settings.c
index e2ec9bde..2da859ee 100644
--- a/src/arch/x86/core/cpuid_settings.c
+++ b/src/arch/x86/core/cpuid_settings.c
@@ -117,7 +117,7 @@ enum cpuid_registers {
 #define CPUID_NUM_REGISTERS( tag ) ( ( ( (tag) >> 16 ) & 0x3 ) + 1 )
 
 /** CPUID settings scope */
-static struct settings_scope cpuid_settings_scope;
+static const struct settings_scope cpuid_settings_scope;
 
 /**
  * Check applicability of CPUID setting
@@ -127,7 +127,7 @@ static struct settings_scope cpuid_settings_scope;
  * @ret applies		Setting applies within this settings block
  */
 static int cpuid_settings_applies ( struct settings *settings __unused,
-				    struct setting *setting ) {
+				    const struct setting *setting ) {
 
 	return ( setting->scope == &cpuid_settings_scope );
 }
@@ -252,7 +252,7 @@ struct init_fn cpuid_settings_init_fn __init_fn ( INIT_NORMAL ) = {
 };
 
 /** CPUID predefined settings */
-struct setting cpuid_predefined_settings[] __setting ( SETTING_HOST_EXTRA ) = {
+const struct setting cpuid_predefined_settings[] __setting ( SETTING_HOST_EXTRA ) = {
 	{
 		.name = "cpuvendor",
 		.description = "CPU vendor",
diff --git a/src/core/memmap_settings.c b/src/core/memmap_settings.c
index f06b8750..906fba12 100644
--- a/src/core/memmap_settings.c
+++ b/src/core/memmap_settings.c
@@ -108,7 +108,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #define MEMMAP_SCALE( tag ) ( (tag) & 0x3f )
 
 /** Memory map settings scope */
-static struct settings_scope memmap_settings_scope;
+static const struct settings_scope memmap_settings_scope;
 
 /**
  * Check applicability of memory map setting
@@ -118,7 +118,7 @@ static struct settings_scope memmap_settings_scope;
  * @ret applies		Setting applies within this settings block
  */
 static int memmap_settings_applies ( struct settings *settings __unused,
-				     struct setting *setting ) {
+				     const struct setting *setting ) {
 
 	return ( setting->scope == &memmap_settings_scope );
 }
@@ -231,7 +231,7 @@ struct init_fn memmap_settings_init_fn __init_fn ( INIT_NORMAL ) = {
 };
 
 /** Memory map predefined settings */
-struct setting memmap_predefined_settings[] __setting ( SETTING_MISC ) = {
+const struct setting memmap_predefined_settings[] __setting ( SETTING_MISC ) = {
 	{
 		.name = "memsize",
 		.description = "Memory size (in MB)",
diff --git a/src/core/nvo.c b/src/core/nvo.c
index 4c871b2f..e135d2b4 100644
--- a/src/core/nvo.c
+++ b/src/core/nvo.c
@@ -193,7 +193,7 @@ static int nvo_save ( struct nvo_block *nvo ) {
  * @ret applies		Setting applies within this settings block
  */
 int nvo_applies ( struct settings *settings __unused,
-		  struct setting *setting ) {
+		  const struct setting *setting ) {
 
 	return ( ( setting->scope == NULL ) &&
 		 dhcpopt_applies ( setting->tag ) );
@@ -208,7 +208,7 @@ int nvo_applies ( struct settings *settings __unused,
  * @v len		Length of setting data
  * @ret rc		Return status code
  */
-static int nvo_store ( struct settings *settings, struct setting *setting,
+static int nvo_store ( struct settings *settings, const struct setting *setting,
 		       const void *data, size_t len ) {
 	struct nvo_block *nvo =
 		container_of ( settings, struct nvo_block, settings );
diff --git a/src/core/settings.c b/src/core/settings.c
index 03ef084a..e6cfc0d2 100644
--- a/src/core/settings.c
+++ b/src/core/settings.c
@@ -96,7 +96,7 @@ static inline void * generic_setting_data ( struct generic_setting *generic ) {
  */
 static struct generic_setting *
 find_generic_setting ( struct generic_settings *generics,
-		       struct setting *setting ) {
+		       const struct setting *setting ) {
 	struct generic_setting *generic;
 
 	list_for_each_entry ( generic, &generics->list, list ) {
@@ -116,7 +116,7 @@ find_generic_setting ( struct generic_settings *generics,
  * @ret rc		Return status code
  */
 int generic_settings_store ( struct settings *settings,
-			     struct setting *setting,
+			     const struct setting *setting,
 			     const void *data, size_t len ) {
 	struct generic_settings *generics =
 		container_of ( settings, struct generic_settings, settings );
@@ -551,7 +551,8 @@ struct settings * settings_target ( struct settings *settings ) {
  * @v setting		Setting
  * @ret applies		Setting applies within this settings block
  */
-int setting_applies ( struct settings *settings, struct setting *setting ) {
+int setting_applies ( struct settings *settings,
+		      const struct setting *setting ) {
 
 	/* Find target settings block */
 	settings = settings_target ( settings );
@@ -570,7 +571,7 @@ int setting_applies ( struct settings *settings, struct setting *setting ) {
  * @v len		Length of setting data
  * @ret rc		Return status code
  */
-int store_setting ( struct settings *settings, struct setting *setting,
+int store_setting ( struct settings *settings, const struct setting *setting,
 		    const void *data, size_t len ) {
 	int rc;
 
@@ -609,11 +610,12 @@ int store_setting ( struct settings *settings, struct setting *setting,
 }
 
 /**
- * Fetch value and origin of setting
+ * Fetch setting
  *
  * @v settings		Settings block, or NULL to search all blocks
  * @v setting		Setting to fetch
- * @v origin		Origin of setting to fill in
+ * @v origin		Origin of setting to fill in, or NULL
+ * @v fetched		Fetched setting to fill in, or NULL
  * @v data		Buffer to fill with setting data
  * @v len		Length of buffer
  * @ret len		Length of setting data, or negative error
@@ -621,17 +623,19 @@ int store_setting ( struct settings *settings, struct setting *setting,
  * The actual length of the setting will be returned even if
  * the buffer was too small.
  */
-static int fetch_setting_and_origin ( struct settings *settings,
-				      struct setting *setting,
-				      struct settings **origin,
-				      void *data, size_t len ) {
+int fetch_setting ( struct settings *settings, const struct setting *setting,
+		    struct settings **origin, struct setting *fetched,
+		    void *data, size_t len ) {
 	struct settings *child;
+	struct setting tmp;
 	int ret;
 
 	/* Avoid returning uninitialised data on error */
 	memset ( data, 0, len );
 	if ( origin )
 		*origin = NULL;
+	if ( fetched )
+		memcpy ( fetched, setting, sizeof ( *fetched ) );
 
 	/* Find target settings block */
 	settings = settings_target ( settings );
@@ -641,22 +645,33 @@ static int fetch_setting_and_origin ( struct settings *settings,
 		return -ENOTSUP;
 
 	/* Try this block first, if applicable */
-	if ( setting_applies ( settings, setting ) &&
-	     ( ( ret = settings->op->fetch ( settings, setting,
-					     data, len ) ) >= 0 ) ) {
-		/* Record origin, if applicable */
-		if ( origin )
-			*origin = settings;
-		/* Default to string setting type, if not yet specified */
-		if ( ! setting->type )
-			setting->type = &setting_type_string;
-		return ret;
+	if ( setting_applies ( settings, setting ) ) {
+
+		/* Create modifiable copy of setting */
+		memcpy ( &tmp, setting, sizeof ( tmp ) );
+		if ( ( ret = settings->op->fetch ( settings, &tmp,
+						   data, len ) ) >= 0 ) {
+
+			/* Default to string type, if not yet specified */
+			if ( ! tmp.type )
+				tmp.type = &setting_type_string;
+
+			/* Record origin, if applicable */
+			if ( origin )
+				*origin = settings;
+
+			/* Record fetched setting, if applicable */
+			if ( fetched )
+				memcpy ( fetched, &tmp, sizeof ( *fetched ) );
+
+			return ret;
+		}
 	}
 
 	/* Recurse into each child block in turn */
 	list_for_each_entry ( child, &settings->children, siblings ) {
-		if ( ( ret = fetch_setting_and_origin ( child, setting, origin,
-							data, len ) ) >= 0 )
+		if ( ( ret = fetch_setting ( child, setting, origin, fetched,
+					     data, len ) ) >= 0 )
 			return ret;
 	}
 
@@ -664,56 +679,95 @@ static int fetch_setting_and_origin ( struct settings *settings,
 }
 
 /**
- * Fetch value of setting
+ * Fetch allocated copy of setting
  *
  * @v settings		Settings block, or NULL to search all blocks
  * @v setting		Setting to fetch
- * @v data		Buffer to fill with setting data
- * @v len		Length of buffer
- * @ret len		Length of setting data, or negative error
+ * @v origin		Origin of setting to fill in, or NULL
+ * @v fetched		Fetched setting to fill in, or NULL
+ * @v data		Buffer to allocate and fill with setting data
+ * @v alloc		Allocation function
+ * @ret len		Length of setting, or negative error
  *
- * The actual length of the setting will be returned even if
- * the buffer was too small.
+ * The caller is responsible for eventually freeing the allocated
+ * buffer.
  */
-int fetch_setting ( struct settings *settings, struct setting *setting,
-		    void *data, size_t len ) {
-	return fetch_setting_and_origin ( settings, setting, NULL, data, len );
+static int fetch_setting_alloc ( struct settings *settings,
+				 const struct setting *setting,
+				 struct settings **origin,
+				 struct setting *fetched,
+				 void **data,
+				 void * ( * alloc ) ( size_t len ) ) {
+	struct settings *tmp_origin;
+	struct setting tmp_fetched;
+	int len;
+	int check_len;
+
+	/* Use local buffers if necessary */
+	if ( ! origin )
+		origin = &tmp_origin;
+	if ( ! fetched )
+		fetched = &tmp_fetched;
+
+	/* Avoid returning uninitialised data on error */
+	*data = NULL;
+
+	/* Check existence, and fetch setting length */
+	len = fetch_setting ( settings, setting, origin, fetched, NULL, 0 );
+	if ( len < 0 )
+		return len;
+
+	/* Allocate buffer */
+	*data = alloc ( len );
+	if ( ! *data )
+		return -ENOMEM;
+
+	/* Fetch setting value */
+	check_len = fetch_setting ( *origin, fetched, NULL, NULL, *data, len );
+	assert ( check_len == len );
+	return len;
 }
 
 /**
- * Fetch origin of setting
+ * Fetch copy of setting
  *
  * @v settings		Settings block, or NULL to search all blocks
  * @v setting		Setting to fetch
- * @ret origin		Origin of setting, or NULL if not found
+ * @v origin		Origin of setting to fill in, or NULL
+ * @v fetched		Fetched setting to fill in, or NULL
+ * @v data		Buffer to allocate and fill with setting data
+ * @ret len		Length of setting, or negative error
  *
- * This function can also be used as an existence check for the
- * setting.
+ * The caller is responsible for eventually freeing the allocated
+ * buffer.
  */
-struct settings * fetch_setting_origin ( struct settings *settings,
-					 struct setting *setting ) {
-	struct settings *origin;
+int fetch_setting_copy ( struct settings *settings,
+			 const struct setting *setting,
+			 struct settings **origin, struct setting *fetched,
+			 void **data ) {
 
-	fetch_setting_and_origin ( settings, setting, &origin, NULL, 0 );
-	return origin;
+	return fetch_setting_alloc ( settings, setting, origin, fetched,
+				     data, malloc );
 }
 
 /**
- * Fetch length of setting
+ * Fetch value of setting
  *
  * @v settings		Settings block, or NULL to search all blocks
  * @v setting		Setting to fetch
- * @ret len		Length of setting data, or negative error
- *
- * This function can also be used as an existence check for the
- * setting.
+ * @v data		Buffer to fill with setting string data
+ * @v len		Length of buffer
+ * @ret len		Length of setting, or negative error
  */
-int fetch_setting_len ( struct settings *settings, struct setting *setting ) {
-	return fetch_setting ( settings, setting, NULL, 0 );
+int fetch_raw_setting ( struct settings *settings,
+			const struct setting *setting,
+			void *data, size_t len ) {
+
+	return fetch_setting ( settings, setting, NULL, NULL, data, len );
 }
 
 /**
- * Fetch copy of setting
+ * Fetch value of setting
  *
  * @v settings		Settings block, or NULL to search all blocks
  * @v setting		Setting to fetch
@@ -723,28 +777,11 @@ int fetch_setting_len ( struct settings *settings, struct setting *setting ) {
  * The caller is responsible for eventually freeing the allocated
  * buffer.
  */
-int fetch_setting_copy ( struct settings *settings, struct setting *setting,
-			 void **data ) {
-	int len;
-	int check_len;
-
-	/* Avoid returning uninitialised data on error */
-	*data = NULL;
-
-	/* Check existence, and fetch setting length */
-	len = fetch_setting_len ( settings, setting );
-	if ( len < 0 )
-		return len;
-
-	/* Allocate buffer */
-	*data = malloc ( len );
-	if ( ! *data )
-		return -ENOMEM;
+int fetch_raw_setting_copy ( struct settings *settings,
+			     const struct setting *setting,
+			     void **data ) {
 
-	/* Fetch setting */
-	check_len = fetch_setting ( settings, setting, *data, len );
-	assert ( check_len == len );
-	return len;
+	return fetch_setting_copy ( settings, setting, NULL, NULL, data );
 }
 
 /**
@@ -760,11 +797,23 @@ int fetch_setting_copy ( struct settings *settings, struct setting *setting,
  * The returned length will be the length of the underlying setting
  * data.
  */
-int fetch_string_setting ( struct settings *settings, struct setting *setting,
+int fetch_string_setting ( struct settings *settings,
+			   const struct setting *setting,
 			   char *data, size_t len ) {
+
 	memset ( data, 0, len );
-	return fetch_setting ( settings, setting, data,
-			       ( ( len > 0 ) ? ( len - 1 ) : 0 ) );
+	return fetch_raw_setting ( settings, setting, data,
+				   ( ( len > 0 ) ? ( len - 1 ) : 0 ) );
+}
+
+/**
+ * Allocate memory for copy of string setting
+ *
+ * @v len		Length of setting
+ * @ret ptr		Allocated memory
+ */
+static void * fetch_string_setting_copy_alloc ( size_t len ) {
+	return zalloc ( len + 1 /* NUL */ );
 }
 
 /**
@@ -779,36 +828,13 @@ int fetch_string_setting ( struct settings *settings, struct setting *setting,
  * The returned length will be the length of the underlying setting
  * data.  The caller is responsible for eventually freeing the
  * allocated buffer.
- *
- * To allow the caller to distinguish between a non-existent setting
- * and an error in allocating memory for the copy, this function will
- * return success (and a NULL buffer pointer) for a non-existent
- * setting.
  */
 int fetch_string_setting_copy ( struct settings *settings,
-				struct setting *setting,
-				char **data ) {
-	int len;
-	int check_len = 0;
-
-	/* Avoid returning uninitialised data on error */
-	*data = NULL;
-
-	/* Fetch setting length, and return success if non-existent */
-	len = fetch_setting_len ( settings, setting );
-	if ( len < 0 )
-		return 0;
-
-	/* Allocate string buffer */
-	*data = malloc ( len + 1 );
-	if ( ! *data )
-		return -ENOMEM;
+				const struct setting *setting, char **data ) {
 
-	/* Fetch setting */
-	check_len = fetch_string_setting ( settings, setting, *data,
-					   ( len + 1 ) );
-	assert ( check_len == len );
-	return len;
+	return fetch_setting_alloc ( settings, setting, NULL, NULL,
+				     ( ( void ** ) data ),
+				     fetch_string_setting_copy_alloc );
 }
 
 /**
@@ -821,12 +847,12 @@ int fetch_string_setting_copy ( struct settings *settings,
  * @ret len		Length of setting, or negative error
  */
 int fetch_ipv4_array_setting ( struct settings *settings,
-			       struct setting *setting,
+			       const struct setting *setting,
 			       struct in_addr *inp, unsigned int count ) {
 	int len;
 
-	len = fetch_setting ( settings, setting, inp,
-			      ( sizeof ( *inp ) * count ) );
+	len = fetch_raw_setting ( settings, setting, inp,
+				  ( sizeof ( *inp ) * count ) );
 	if ( len < 0 )
 		return len;
 	if ( ( len % sizeof ( *inp ) ) != 0 )
@@ -842,8 +868,10 @@ int fetch_ipv4_array_setting ( struct settings *settings,
  * @v inp		IPv4 address to fill in
  * @ret len		Length of setting, or negative error
  */
-int fetch_ipv4_setting ( struct settings *settings, struct setting *setting,
+int fetch_ipv4_setting ( struct settings *settings,
+			 const struct setting *setting,
 			 struct in_addr *inp ) {
+
 	return fetch_ipv4_array_setting ( settings, setting, inp, 1 );
 }
 
@@ -887,7 +915,8 @@ static int numeric_setting_value ( int is_signed, const void *raw, size_t len,
  * @v value		Integer value to fill in
  * @ret len		Length of setting, or negative error
  */
-int fetch_numeric_setting ( struct settings *settings, struct setting *setting,
+int fetch_numeric_setting ( struct settings *settings,
+			    const struct setting *setting,
 			    unsigned long *value, int is_signed ) {
 	unsigned long tmp;
 	int len;
@@ -896,7 +925,7 @@ int fetch_numeric_setting ( struct settings *settings, struct setting *setting,
 	*value = 0;
 
 	/* Fetch raw (network-ordered, variable-length) setting */
-	len = fetch_setting ( settings, setting, &tmp, sizeof ( tmp ) );
+	len = fetch_raw_setting ( settings, setting, &tmp, sizeof ( tmp ) );
 	if ( len < 0 )
 		return len;
 
@@ -912,7 +941,8 @@ int fetch_numeric_setting ( struct settings *settings, struct setting *setting,
  * @v value		Integer value to fill in
  * @ret len		Length of setting, or negative error
  */
-int fetch_int_setting ( struct settings *settings, struct setting *setting,
+int fetch_int_setting ( struct settings *settings,
+			const struct setting *setting,
 			long *value ) {
 
 	return fetch_numeric_setting ( settings, setting,
@@ -927,7 +957,8 @@ int fetch_int_setting ( struct settings *settings, struct setting *setting,
  * @v value		Integer value to fill in
  * @ret len		Length of setting, or negative error
  */
-int fetch_uint_setting ( struct settings *settings, struct setting *setting,
+int fetch_uint_setting ( struct settings *settings,
+			 const struct setting *setting,
 			 unsigned long *value ) {
 
 	return fetch_numeric_setting ( settings, setting, value, 0 );
@@ -940,7 +971,8 @@ int fetch_uint_setting ( struct settings *settings, struct setting *setting,
  * @v setting		Setting to fetch
  * @ret value		Setting value, or zero
  */
-long fetch_intz_setting ( struct settings *settings, struct setting *setting ){
+long fetch_intz_setting ( struct settings *settings,
+			  const struct setting *setting ) {
 	unsigned long value;
 
 	fetch_numeric_setting ( settings, setting, &value, 1 );
@@ -955,7 +987,7 @@ long fetch_intz_setting ( struct settings *settings, struct setting *setting ){
  * @ret value		Setting value, or zero
  */
 unsigned long fetch_uintz_setting ( struct settings *settings,
-				    struct setting *setting ) {
+				    const struct setting *setting ) {
 	unsigned long value;
 
 	fetch_numeric_setting ( settings, setting, &value, 0 );
@@ -970,11 +1002,12 @@ unsigned long fetch_uintz_setting ( struct settings *settings,
  * @v uuid		UUID to fill in
  * @ret len		Length of setting, or negative error
  */
-int fetch_uuid_setting ( struct settings *settings, struct setting *setting,
+int fetch_uuid_setting ( struct settings *settings,
+			 const struct setting *setting,
 			 union uuid *uuid ) {
 	int len;
 
-	len = fetch_setting ( settings, setting, uuid, sizeof ( *uuid ) );
+	len = fetch_raw_setting ( settings, setting, uuid, sizeof ( *uuid ) );
 	if ( len < 0 )
 		return len;
 	if ( len != sizeof ( *uuid ) )
@@ -1005,7 +1038,7 @@ void clear_settings ( struct settings *settings ) {
  * @ret 0		Settings are the same
  * @ret non-zero	Settings are not the same
  */
-int setting_cmp ( struct setting *a, struct setting *b ) {
+int setting_cmp ( const struct setting *a, const struct setting *b ) {
 
 	/* If the settings have tags, compare them */
 	if ( a->tag && ( a->tag == b->tag ) && ( a->scope == b->scope ) )
@@ -1036,7 +1069,7 @@ int setting_cmp ( struct setting *a, struct setting *b ) {
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-int setting_format ( struct setting_type *type, const void *raw,
+int setting_format ( const struct setting_type *type, const void *raw,
 		     size_t raw_len, char *buf, size_t len ) {
 
 	/* Sanity check */
@@ -1055,7 +1088,7 @@ int setting_format ( struct setting_type *type, const void *raw,
  * @v len		Length of buffer
  * @ret len		Length of raw value, or negative error
  */
-int setting_parse ( struct setting_type *type, const char *value,
+int setting_parse ( const struct setting_type *type, const char *value,
 		    void *buf, size_t len ) {
 
 	/* Sanity check */
@@ -1074,7 +1107,7 @@ int setting_parse ( struct setting_type *type, const char *value,
  * @ret value		Numeric value
  * @ret rc		Return status code
  */
-int setting_numerate ( struct setting_type *type, const void *raw,
+int setting_numerate ( const struct setting_type *type, const void *raw,
 		       size_t raw_len, unsigned long *value ) {
 
 	/* Sanity check */
@@ -1093,7 +1126,7 @@ int setting_numerate ( struct setting_type *type, const void *raw,
  * @v len		Length of buffer
  * @ret len		Length of raw value, or negative error
  */
-int setting_denumerate ( struct setting_type *type, unsigned long value,
+int setting_denumerate ( const struct setting_type *type, unsigned long value,
 			 void *buf, size_t len ) {
 
 	/* Sanity check */
@@ -1108,28 +1141,37 @@ int setting_denumerate ( struct setting_type *type, unsigned long value,
  *
  * @v settings		Settings block, or NULL to search all blocks
  * @v setting		Setting to fetch
+ * @v origin		Origin of setting to fill in, or NULL
+ * @v fetched		Fetched setting to fill in, or NULL
  * @v buf		Buffer to contain formatted value
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-int fetchf_setting ( struct settings *settings, struct setting *setting,
+int fetchf_setting ( struct settings *settings, const struct setting *setting,
+		     struct settings **origin, struct setting *fetched,
 		     char *buf, size_t len ) {
+	struct setting tmp_fetched;
 	void *raw;
 	int raw_len;
 	int ret;
 
+	/* Use local buffers if necessary */
+	if ( ! fetched )
+		fetched = &tmp_fetched;
+
 	/* Fetch raw value */
-	raw_len = fetch_setting_copy ( settings, setting, &raw );
+	raw_len = fetch_setting_copy ( settings, setting, origin, fetched,
+				       &raw );
 	if ( raw_len < 0 ) {
 		ret = raw_len;
 		goto err_fetch_copy;
 	}
 
 	/* Sanity check */
-	assert ( setting->type != NULL );
+	assert ( fetched->type != NULL );
 
 	/* Format setting */
-	if ( ( ret = setting_format ( setting->type, raw, raw_len, buf,
+	if ( ( ret = setting_format ( fetched->type, raw, raw_len, buf,
 				      len ) ) < 0 )
 		goto err_format;
 
@@ -1144,22 +1186,34 @@ int fetchf_setting ( struct settings *settings, struct setting *setting,
  *
  * @v settings		Settings block, or NULL to search all blocks
  * @v setting		Setting to fetch
+ * @v origin		Origin of setting to fill in, or NULL
+ * @v fetched		Fetched setting to fill in, or NULL
  * @v value		Buffer to allocate and fill with formatted value
  * @ret len		Length of formatted value, or negative error
  *
  * The caller is responsible for eventually freeing the allocated
  * buffer.
  */
-int fetchf_setting_copy ( struct settings *settings, struct setting *setting,
+int fetchf_setting_copy ( struct settings *settings,
+			  const struct setting *setting,
+			  struct settings **origin, struct setting *fetched,
 			  char **value ) {
+	struct settings *tmp_origin;
+	struct setting tmp_fetched;
 	int len;
 	int check_len;
 
+	/* Use local buffers if necessary */
+	if ( ! origin )
+		origin = &tmp_origin;
+	if ( ! fetched )
+		fetched = &tmp_fetched;
+
 	/* Avoid returning uninitialised data on error */
 	*value = NULL;
 
 	/* Check existence, and fetch formatted value length */
-	len = fetchf_setting ( settings, setting, NULL, 0 );
+	len = fetchf_setting ( settings, setting, origin, fetched, NULL, 0 );
 	if ( len < 0 )
 		return len;
 
@@ -1169,7 +1223,7 @@ int fetchf_setting_copy ( struct settings *settings, struct setting *setting,
 		return -ENOMEM;
 
 	/* Fetch formatted value */
-	check_len = fetchf_setting ( settings, setting, *value,
+	check_len = fetchf_setting ( *origin, fetched, NULL, NULL, *value,
 				     ( len + 1 /* NUL */ ) );
 	assert ( check_len == len );
 	return len;
@@ -1183,7 +1237,7 @@ int fetchf_setting_copy ( struct settings *settings, struct setting *setting,
  * @v value		Formatted setting data, or NULL
  * @ret rc		Return status code
  */
-int storef_setting ( struct settings *settings, struct setting *setting,
+int storef_setting ( struct settings *settings, const struct setting *setting,
 		     const char *value ) {
 	void *raw;
 	int raw_len;
@@ -1231,27 +1285,36 @@ int storef_setting ( struct settings *settings, struct setting *setting,
  *
  * @v settings		Settings block, or NULL to search all blocks
  * @v setting		Setting to fetch
+ * @v origin		Origin of setting to fill in, or NULL
+ * @v fetched		Fetched setting to fill in, or NULL
  * @v value		Numeric value to fill in
  * @ret rc		Return status code
  */
-int fetchn_setting ( struct settings *settings, struct setting *setting,
+int fetchn_setting ( struct settings *settings, const struct setting *setting,
+		     struct settings **origin, struct setting *fetched,
 		     unsigned long *value ) {
+	struct setting tmp_fetched;
 	void *raw;
 	int raw_len;
 	int rc;
 
+	/* Use local buffers if necessary */
+	if ( ! fetched )
+		fetched = &tmp_fetched;
+
 	/* Fetch raw value */
-	raw_len = fetch_setting_copy ( settings, setting, &raw );
+	raw_len = fetch_setting_copy ( settings, setting, origin, fetched,
+				       &raw );
 	if ( raw_len < 0 ) {
 		rc = raw_len;
 		goto err_fetch_copy;
 	}
 
 	/* Sanity check */
-	assert ( setting->type != NULL );
+	assert ( fetched->type != NULL );
 
 	/* Numerate setting */
-	if ( ( rc = setting_numerate ( setting->type, raw, raw_len,
+	if ( ( rc = setting_numerate ( fetched->type, raw, raw_len,
 				       value ) ) < 0 )
 		goto err_numerate;
 
@@ -1269,7 +1332,7 @@ int fetchn_setting ( struct settings *settings, struct setting *setting,
  * @v value		Numeric value
  * @ret rc		Return status code
  */
-int storen_setting ( struct settings *settings, struct setting *setting,
+int storen_setting ( struct settings *settings, const struct setting *setting,
 		     unsigned long value ) {
 	void *raw;
 	int raw_len;
@@ -1357,8 +1420,8 @@ static unsigned int parse_setting_tag ( const char *name ) {
  * @v name		Name
  * @ret type		Setting type, or NULL
  */
-static struct setting_type * find_setting_type ( const char *name ) {
-	struct setting_type *type;
+static const struct setting_type * find_setting_type ( const char *name ) {
+	const struct setting_type *type;
 
 	for_each_table_entry ( type, SETTING_TYPES ) {
 		if ( strcmp ( name, type->name ) == 0 )
@@ -1461,7 +1524,7 @@ int parse_setting_name ( char *name, get_child_settings_t get_child,
  * @v len		Length of buffer
  * @ret len		Length of setting name, or negative error
  */
-int setting_name ( struct settings *settings, struct setting *setting,
+int setting_name ( struct settings *settings, const struct setting *setting,
 		   char *buf, size_t len ) {
 	const char *name;
 
@@ -1487,7 +1550,7 @@ int setting_name ( struct settings *settings, struct setting *setting,
  * @v len		Length of buffer
  * @ret len		Length of raw value, or negative error
  */
-static int parse_string_setting ( struct setting_type *type __unused,
+static int parse_string_setting ( const struct setting_type *type __unused,
 				  const char *value, void *buf, size_t len ) {
 	size_t raw_len = strlen ( value ); /* Exclude terminating NUL */
 
@@ -1509,7 +1572,7 @@ static int parse_string_setting ( struct setting_type *type __unused,
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-static int format_string_setting ( struct setting_type *type __unused,
+static int format_string_setting ( const struct setting_type *type __unused,
 				   const void *raw, size_t raw_len, char *buf,
 				   size_t len ) {
 
@@ -1523,7 +1586,7 @@ static int format_string_setting ( struct setting_type *type __unused,
 }
 
 /** A string setting type */
-struct setting_type setting_type_string __setting_type = {
+const struct setting_type setting_type_string __setting_type = {
 	.name = "string",
 	.parse = parse_string_setting,
 	.format = format_string_setting,
@@ -1538,7 +1601,7 @@ struct setting_type setting_type_string __setting_type = {
  * @v len		Length of buffer
  * @ret len		Length of raw value, or negative error
  */
-static int parse_uristring_setting ( struct setting_type *type __unused,
+static int parse_uristring_setting ( const struct setting_type *type __unused,
 				     const char *value, void *buf, size_t len ){
 	char tmp[ len + 1 /* NUL */ ];
 	size_t raw_len;
@@ -1564,7 +1627,7 @@ static int parse_uristring_setting ( struct setting_type *type __unused,
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-static int format_uristring_setting ( struct setting_type *type __unused,
+static int format_uristring_setting ( const struct setting_type *type __unused,
 				      const void *raw, size_t raw_len,
 				      char *buf, size_t len ) {
 	char tmp[ raw_len + 1 /* NUL */ ];
@@ -1578,7 +1641,7 @@ static int format_uristring_setting ( struct setting_type *type __unused,
 }
 
 /** A URI-encoded string setting type */
-struct setting_type setting_type_uristring __setting_type = {
+const struct setting_type setting_type_uristring __setting_type = {
 	.name = "uristring",
 	.parse = parse_uristring_setting,
 	.format = format_uristring_setting,
@@ -1593,7 +1656,7 @@ struct setting_type setting_type_uristring __setting_type = {
  * @v len		Length of buffer
  * @ret len		Length of raw value, or negative error
  */
-static int parse_ipv4_setting ( struct setting_type *type __unused,
+static int parse_ipv4_setting ( const struct setting_type *type __unused,
 				const char *value, void *buf, size_t len ) {
 	struct in_addr ipv4;
 
@@ -1619,7 +1682,7 @@ static int parse_ipv4_setting ( struct setting_type *type __unused,
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-static int format_ipv4_setting ( struct setting_type *type __unused,
+static int format_ipv4_setting ( const struct setting_type *type __unused,
 				 const void *raw, size_t raw_len, char *buf,
 				 size_t len ) {
 	const struct in_addr *ipv4 = raw;
@@ -1630,7 +1693,7 @@ static int format_ipv4_setting ( struct setting_type *type __unused,
 }
 
 /** An IPv4 address setting type */
-struct setting_type setting_type_ipv4 __setting_type = {
+const struct setting_type setting_type_ipv4 __setting_type = {
 	.name = "ipv4",
 	.parse = parse_ipv4_setting,
 	.format = format_ipv4_setting,
@@ -1685,7 +1748,7 @@ static const char setting_type_int_name[][8] = {
  * @v type		Setting type
  * @ret index		Integer setting type index
  */
-static unsigned int setting_type_int_index ( struct setting_type *type ) {
+static unsigned int setting_type_int_index ( const struct setting_type *type ) {
 
 	return ( ( type->name - setting_type_int_name[0] ) /
 		 sizeof ( setting_type_int_name[0] ) );
@@ -1697,7 +1760,7 @@ static unsigned int setting_type_int_index ( struct setting_type *type ) {
  * @v type		Setting type
  * @ret index		Integer setting type width
  */
-static unsigned int setting_type_int_width ( struct setting_type *type ) {
+static unsigned int setting_type_int_width ( const struct setting_type *type ) {
 
 	return ( 1 << setting_type_int_index ( type ) );
 }
@@ -1708,7 +1771,7 @@ static unsigned int setting_type_int_width ( struct setting_type *type ) {
  * @v type		Setting type
  * @ret is_signed	Integer setting type is signed
  */
-static int setting_type_int_is_signed ( struct setting_type *type ) {
+static int setting_type_int_is_signed ( const struct setting_type *type ) {
 	return ( ( type->name - setting_type_int_name[0] ) & 1 );
 }
 
@@ -1721,7 +1784,7 @@ static int setting_type_int_is_signed ( struct setting_type *type ) {
  * @v len		Length of buffer
  * @ret len		Length of raw value, or negative error
  */
-static int denumerate_int_setting ( struct setting_type *type,
+static int denumerate_int_setting ( const struct setting_type *type,
 				    unsigned long value, void *buf,
 				    size_t len ) {
 	unsigned int size = setting_type_int_width ( type );
@@ -1747,7 +1810,7 @@ static int denumerate_int_setting ( struct setting_type *type,
  * @v value		Numeric value to fill in
  * @ret rc		Return status code
  */
-static int numerate_int_setting ( struct setting_type *type,
+static int numerate_int_setting ( const struct setting_type *type,
 				  const void *raw, size_t raw_len,
 				  unsigned long *value ) {
 	int is_signed = setting_type_int_is_signed ( type );
@@ -1771,8 +1834,8 @@ static int numerate_int_setting ( struct setting_type *type,
  * @v len		Length of buffer
  * @ret len		Length of raw value, or negative error
  */
-static int parse_int_setting ( struct setting_type *type, const char *value,
-			       void *buf, size_t len ) {
+static int parse_int_setting ( const struct setting_type *type,
+			       const char *value, void *buf, size_t len ) {
 	char *endp;
 	unsigned long num_value;
 
@@ -1794,8 +1857,9 @@ static int parse_int_setting ( struct setting_type *type, const char *value,
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-static int format_int_setting ( struct setting_type *type, const void *raw,
-				size_t raw_len, char *buf, size_t len ) {
+static int format_int_setting ( const struct setting_type *type,
+				const void *raw, size_t raw_len,
+				char *buf, size_t len ) {
 	unsigned long value;
 	int ret;
 
@@ -1817,8 +1881,9 @@ static int format_int_setting ( struct setting_type *type, const void *raw,
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-static int format_uint_setting ( struct setting_type *type, const void *raw,
-				 size_t raw_len, char *buf, size_t len ) {
+static int format_uint_setting ( const struct setting_type *type,
+				 const void *raw, size_t raw_len,
+				 char *buf, size_t len ) {
 	unsigned long value;
 	int ret;
 
@@ -1859,27 +1924,27 @@ static int format_uint_setting ( struct setting_type *type, const void *raw,
 }
 
 /** A signed 8-bit integer setting type */
-struct setting_type setting_type_int8 __setting_type =
+const struct setting_type setting_type_int8 __setting_type =
 	SETTING_TYPE_INT ( SETTING_TYPE_INT8 );
 
 /** A signed 16-bit integer setting type */
-struct setting_type setting_type_int16 __setting_type =
+const struct setting_type setting_type_int16 __setting_type =
 	SETTING_TYPE_INT ( SETTING_TYPE_INT16 );
 
 /** A signed 32-bit integer setting type */
-struct setting_type setting_type_int32 __setting_type =
+const struct setting_type setting_type_int32 __setting_type =
 	SETTING_TYPE_INT ( SETTING_TYPE_INT32 );
 
 /** An unsigned 8-bit integer setting type */
-struct setting_type setting_type_uint8 __setting_type =
+const struct setting_type setting_type_uint8 __setting_type =
 	SETTING_TYPE_UINT ( SETTING_TYPE_INT8 );
 
 /** An unsigned 16-bit integer setting type */
-struct setting_type setting_type_uint16 __setting_type =
+const struct setting_type setting_type_uint16 __setting_type =
 	SETTING_TYPE_UINT ( SETTING_TYPE_INT16 );
 
 /** An unsigned 32-bit integer setting type */
-struct setting_type setting_type_uint32 __setting_type =
+const struct setting_type setting_type_uint32 __setting_type =
 	SETTING_TYPE_UINT ( SETTING_TYPE_INT32 );
 
 /**
@@ -1918,7 +1983,7 @@ static int format_hex_setting ( const char *delimiter, const void *raw,
  * @v size		Integer size, in bytes
  * @ret len		Length of raw value, or negative error
  */
-static int parse_hex_setting ( struct setting_type *type __unused,
+static int parse_hex_setting ( const struct setting_type *type __unused,
 			       const char *value, void *buf, size_t len ) {
 	return hex_decode ( value, ':', buf, len );
 }
@@ -1933,7 +1998,7 @@ static int parse_hex_setting ( struct setting_type *type __unused,
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-static int format_hex_colon_setting ( struct setting_type *type __unused,
+static int format_hex_colon_setting ( const struct setting_type *type __unused,
 				      const void *raw, size_t raw_len,
 				      char *buf, size_t len ) {
 	return format_hex_setting ( ":", raw, raw_len, buf, len );
@@ -1949,7 +2014,7 @@ static int format_hex_colon_setting ( struct setting_type *type __unused,
  * @v size		Integer size, in bytes
  * @ret len		Length of raw value, or negative error
  */
-static int parse_hex_hyphen_setting ( struct setting_type *type __unused,
+static int parse_hex_hyphen_setting ( const struct setting_type *type __unused,
 				      const char *value, void *buf,
 				      size_t len ) {
 	return hex_decode ( value, '-', buf, len );
@@ -1965,7 +2030,7 @@ static int parse_hex_hyphen_setting ( struct setting_type *type __unused,
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-static int format_hex_hyphen_setting ( struct setting_type *type __unused,
+static int format_hex_hyphen_setting ( const struct setting_type *type __unused,
 				       const void *raw, size_t raw_len,
 				       char *buf, size_t len ) {
 	return format_hex_setting ( "-", raw, raw_len, buf, len );
@@ -1981,7 +2046,7 @@ static int format_hex_hyphen_setting ( struct setting_type *type __unused,
  * @v size		Integer size, in bytes
  * @ret len		Length of raw value, or negative error
  */
-static int parse_hex_raw_setting ( struct setting_type *type __unused,
+static int parse_hex_raw_setting ( const struct setting_type *type __unused,
 				   const char *value, void *buf, size_t len ) {
 	return hex_decode ( value, 0, buf, len );
 }
@@ -1996,28 +2061,28 @@ static int parse_hex_raw_setting ( struct setting_type *type __unused,
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-static int format_hex_raw_setting ( struct setting_type *type __unused,
+static int format_hex_raw_setting ( const struct setting_type *type __unused,
 				    const void *raw, size_t raw_len,
 				    char *buf, size_t len ) {
 	return format_hex_setting ( "", raw, raw_len, buf, len );
 }
 
 /** A hex-string setting (colon-delimited) */
-struct setting_type setting_type_hex __setting_type = {
+const struct setting_type setting_type_hex __setting_type = {
 	.name = "hex",
 	.parse = parse_hex_setting,
 	.format = format_hex_colon_setting,
 };
 
 /** A hex-string setting (hyphen-delimited) */
-struct setting_type setting_type_hexhyp __setting_type = {
+const struct setting_type setting_type_hexhyp __setting_type = {
 	.name = "hexhyp",
 	.parse = parse_hex_hyphen_setting,
 	.format = format_hex_hyphen_setting,
 };
 
 /** A hex-string setting (non-delimited) */
-struct setting_type setting_type_hexraw __setting_type = {
+const struct setting_type setting_type_hexraw __setting_type = {
 	.name = "hexraw",
 	.parse = parse_hex_raw_setting,
 	.format = format_hex_raw_setting,
@@ -2033,7 +2098,7 @@ struct setting_type setting_type_hexraw __setting_type = {
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-static int format_uuid_setting ( struct setting_type *type __unused,
+static int format_uuid_setting ( const struct setting_type *type __unused,
 				 const void *raw, size_t raw_len, char *buf,
 				 size_t len ) {
 	const union uuid *uuid = raw;
@@ -2047,7 +2112,7 @@ static int format_uuid_setting ( struct setting_type *type __unused,
 }
 
 /** UUID setting type */
-struct setting_type setting_type_uuid __setting_type = {
+const struct setting_type setting_type_uuid __setting_type = {
 	.name = "uuid",
 	.format = format_uuid_setting,
 };
@@ -2062,7 +2127,7 @@ struct setting_type setting_type_uuid __setting_type = {
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-static int format_busdevfn_setting ( struct setting_type *type __unused,
+static int format_busdevfn_setting ( const struct setting_type *type __unused,
 				     const void *raw, size_t raw_len, char *buf,
 				     size_t len ) {
 	unsigned long busdevfn;
@@ -2080,7 +2145,7 @@ static int format_busdevfn_setting ( struct setting_type *type __unused,
 }
 
 /** PCI bus:dev.fn setting type */
-struct setting_type setting_type_busdevfn __setting_type = {
+const struct setting_type setting_type_busdevfn __setting_type = {
 	.name = "busdevfn",
 	.format = format_busdevfn_setting,
 };
@@ -2153,7 +2218,8 @@ char * expand_settings ( const char *string ) {
 			/* Fetch and format setting value.  Ignore
 			 * errors; treat non-existent settings as empty.
 			 */
-			fetchf_setting_copy ( settings, &setting, &value );
+			fetchf_setting_copy ( settings, &setting, NULL, NULL,
+					      &value );
 		}
 
 		/* Construct expanded string and discard old string */
@@ -2177,7 +2243,7 @@ char * expand_settings ( const char *string ) {
  */
 
 /** Hostname setting */
-struct setting hostname_setting __setting ( SETTING_HOST ) = {
+const struct setting hostname_setting __setting ( SETTING_HOST ) = {
 	.name = "hostname",
 	.description = "Host name",
 	.tag = DHCP_HOST_NAME,
@@ -2185,7 +2251,7 @@ struct setting hostname_setting __setting ( SETTING_HOST ) = {
 };
 
 /** Domain name setting */
-struct setting domain_setting __setting ( SETTING_IPv4_EXTRA ) = {
+const struct setting domain_setting __setting ( SETTING_IPv4_EXTRA ) = {
 	.name = "domain",
 	.description = "DNS domain",
 	.tag = DHCP_DOMAIN_NAME,
@@ -2193,7 +2259,7 @@ struct setting domain_setting __setting ( SETTING_IPv4_EXTRA ) = {
 };
 
 /** TFTP server setting */
-struct setting next_server_setting __setting ( SETTING_BOOT ) = {
+const struct setting next_server_setting __setting ( SETTING_BOOT ) = {
 	.name = "next-server",
 	.description = "TFTP server",
 	.tag = DHCP_EB_SIADDR,
@@ -2201,7 +2267,7 @@ struct setting next_server_setting __setting ( SETTING_BOOT ) = {
 };
 
 /** Filename setting */
-struct setting filename_setting __setting ( SETTING_BOOT ) = {
+const struct setting filename_setting __setting ( SETTING_BOOT ) = {
 	.name = "filename",
 	.description = "Boot filename",
 	.tag = DHCP_BOOTFILE_NAME,
@@ -2209,7 +2275,7 @@ struct setting filename_setting __setting ( SETTING_BOOT ) = {
 };
 
 /** Root path setting */
-struct setting root_path_setting __setting ( SETTING_SANBOOT ) = {
+const struct setting root_path_setting __setting ( SETTING_SANBOOT ) = {
 	.name = "root-path",
 	.description = "SAN root path",
 	.tag = DHCP_ROOT_PATH,
@@ -2217,7 +2283,7 @@ struct setting root_path_setting __setting ( SETTING_SANBOOT ) = {
 };
 
 /** Username setting */
-struct setting username_setting __setting ( SETTING_AUTH ) = {
+const struct setting username_setting __setting ( SETTING_AUTH ) = {
 	.name = "username",
 	.description = "User name",
 	.tag = DHCP_EB_USERNAME,
@@ -2225,7 +2291,7 @@ struct setting username_setting __setting ( SETTING_AUTH ) = {
 };
 
 /** Password setting */
-struct setting password_setting __setting ( SETTING_AUTH ) = {
+const struct setting password_setting __setting ( SETTING_AUTH ) = {
 	.name = "password",
 	.description = "Password",
 	.tag = DHCP_EB_PASSWORD,
@@ -2233,7 +2299,7 @@ struct setting password_setting __setting ( SETTING_AUTH ) = {
 };
 
 /** Priority setting */
-struct setting priority_setting __setting ( SETTING_MISC ) = {
+const struct setting priority_setting __setting ( SETTING_MISC ) = {
 	.name = "priority",
 	.description = "Settings priority",
 	.tag = DHCP_EB_PRIORITY,
@@ -2241,7 +2307,7 @@ struct setting priority_setting __setting ( SETTING_MISC ) = {
 };
 
 /** DHCP user class setting */
-struct setting user_class_setting __setting ( SETTING_HOST_EXTRA ) = {
+const struct setting user_class_setting __setting ( SETTING_HOST_EXTRA ) = {
 	.name = "user-class",
 	.description = "DHCP user class",
 	.tag = DHCP_USER_CLASS_ID,
@@ -2256,7 +2322,7 @@ struct setting user_class_setting __setting ( SETTING_HOST_EXTRA ) = {
  */
 
 /** Built-in setting scope */
-struct settings_scope builtin_scope;
+const struct settings_scope builtin_scope;
 
 /**
  * Fetch error number setting
@@ -2277,7 +2343,7 @@ static int errno_fetch ( void *data, size_t len ) {
 }
 
 /** Error number setting */
-struct setting errno_setting __setting ( SETTING_MISC ) = {
+const struct setting errno_setting __setting ( SETTING_MISC ) = {
 	.name = "errno",
 	.description = "Last error",
 	.type = &setting_type_uint32,
@@ -2305,7 +2371,7 @@ static int buildarch_fetch ( void *data, size_t len ) {
 }
 
 /** Build architecture setting */
-struct setting buildarch_setting __setting ( SETTING_MISC ) = {
+const struct setting buildarch_setting __setting ( SETTING_MISC ) = {
 	.name = "buildarch",
 	.description = "Build architecture",
 	.type = &setting_type_string,
@@ -2333,7 +2399,7 @@ static int platform_fetch ( void *data, size_t len ) {
 }
 
 /** Platform setting */
-struct setting platform_setting __setting ( SETTING_MISC ) = {
+const struct setting platform_setting __setting ( SETTING_MISC ) = {
 	.name = "platform",
 	.description = "Platform",
 	.type = &setting_type_string,
@@ -2359,7 +2425,7 @@ static int version_fetch ( void *data, size_t len ) {
 }
 
 /** Version setting */
-struct setting version_setting __setting ( SETTING_MISC ) = {
+const struct setting version_setting __setting ( SETTING_MISC ) = {
 	.name = "version",
 	.description = "Version",
 	.type = &setting_type_string,
@@ -2401,7 +2467,7 @@ static int builtin_fetch ( struct settings *settings __unused,
  * @ret applies		Setting applies within this settings block
  */
 static int builtin_applies ( struct settings *settings __unused,
-			     struct setting *setting ) {
+			     const struct setting *setting ) {
 
 	return ( setting->scope == &builtin_scope );
 }
diff --git a/src/crypto/clientcert.c b/src/crypto/clientcert.c
index 6f6bf113..b09c880a 100644
--- a/src/crypto/clientcert.c
+++ b/src/crypto/clientcert.c
@@ -128,8 +128,8 @@ static int clientcert_apply_settings ( void ) {
 
 		/* Fetch new client certificate, if any */
 		free ( cert );
-		if ( ( len = fetch_setting_copy ( NULL, &cert_setting,
-						  &cert ) ) >= 0 ) {
+		if ( ( len = fetch_raw_setting_copy ( NULL, &cert_setting,
+						      &cert ) ) >= 0 ) {
 			client_certificate.data = cert;
 			client_certificate.len = len;
 		}
@@ -140,8 +140,8 @@ static int clientcert_apply_settings ( void ) {
 
 		/* Fetch new client private key, if any */
 		free ( key );
-		if ( ( len = fetch_setting_copy ( NULL, &privkey_setting,
-						  &key ) ) >= 0 ) {
+		if ( ( len = fetch_raw_setting_copy ( NULL, &privkey_setting,
+						      &key ) ) >= 0 ) {
 			client_private_key.data = key;
 			client_private_key.len = len;
 		}
diff --git a/src/crypto/rootcert.c b/src/crypto/rootcert.c
index 2aa31334..cfeabb81 100644
--- a/src/crypto/rootcert.c
+++ b/src/crypto/rootcert.c
@@ -100,8 +100,8 @@ static void rootcert_init ( void ) {
 		/* Fetch copy of "trust" setting, if it exists.  This
 		 * memory will never be freed.
 		 */
-		if ( ( len = fetch_setting_copy ( NULL, &trust_setting,
-						  &external ) ) >= 0 ) {
+		if ( ( len = fetch_raw_setting_copy ( NULL, &trust_setting,
+						      &external ) ) >= 0 ) {
 			root_certificates.fingerprints = external;
 			root_certificates.count = ( len / FINGERPRINT_LEN );
 		}
diff --git a/src/drivers/block/ibft.c b/src/drivers/block/ibft.c
index 75ca51a9..0700f8c4 100644
--- a/src/drivers/block/ibft.c
+++ b/src/drivers/block/ibft.c
@@ -107,7 +107,7 @@ static void ibft_set_ipaddr ( struct ibft_ipaddr *ipaddr, struct in_addr in ) {
  * @v count		Maximum number of IP addresses
  */
 static void ibft_set_ipaddr_setting ( struct ibft_ipaddr *ipaddr,
-				      struct setting *setting,
+				      const struct setting *setting,
 				      unsigned int count ) {
 	struct in_addr in[count];
 	unsigned int i;
@@ -183,11 +183,13 @@ static int ibft_set_string ( struct ibft_strings *strings,
  */
 static int ibft_set_string_setting ( struct ibft_strings *strings,
 				     struct ibft_string *string,
-				     struct setting *setting ) {
+				     const struct setting *setting ) {
+	struct settings *origin;
+	struct setting fetched;
 	int len;
 	char *dest;
 
-	len = fetch_setting_len ( NULL, setting );
+	len = fetch_setting ( NULL, setting, &origin, &fetched, NULL, 0 );
 	if ( len < 0 ) {
 		string->offset = 0;
 		string->len = 0;
@@ -197,7 +199,7 @@ static int ibft_set_string_setting ( struct ibft_strings *strings,
 	dest = ibft_alloc_string ( strings, string, len );
 	if ( ! dest )
 		return -ENOBUFS;
-	fetch_string_setting ( NULL, setting, dest, ( len + 1 ) );
+	fetch_string_setting ( origin, &fetched, dest, ( len + 1 ));
 
 	return 0;
 }
diff --git a/src/drivers/bus/pci_settings.c b/src/drivers/bus/pci_settings.c
index a4d7b933..db20452e 100644
--- a/src/drivers/bus/pci_settings.c
+++ b/src/drivers/bus/pci_settings.c
@@ -32,7 +32,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
  */
 
 /** PCI device settings scope */
-static struct settings_scope pci_settings_scope;
+static const struct settings_scope pci_settings_scope;
 
 /**
  * Check applicability of PCI device setting
@@ -42,7 +42,7 @@ static struct settings_scope pci_settings_scope;
  * @ret applies		Setting applies within this settings block
  */
 static int pci_settings_applies ( struct settings *settings __unused,
-				  struct setting *setting ) {
+				  const struct setting *setting ) {
 
 	return ( setting->scope == &pci_settings_scope );
 }
diff --git a/src/drivers/net/phantom/phantom.c b/src/drivers/net/phantom/phantom.c
index 7f2fe0b6..e70ded08 100644
--- a/src/drivers/net/phantom/phantom.c
+++ b/src/drivers/net/phantom/phantom.c
@@ -1455,7 +1455,7 @@ static struct net_device_operations phantom_operations = {
  */
 
 /** Phantom CLP settings scope */
-static struct settings_scope phantom_settings_scope;
+static const struct settings_scope phantom_settings_scope;
 
 /** Phantom CLP data
  *
@@ -1656,7 +1656,7 @@ static int phantom_clp_fetch ( struct phantom_nic *phantom, unsigned int port,
 /** A Phantom CLP setting */
 struct phantom_clp_setting {
 	/** iPXE setting */
-	struct setting *setting;
+	const struct setting *setting;
 	/** Setting number */
 	unsigned int clp_setting;
 };
@@ -1673,7 +1673,8 @@ static struct phantom_clp_setting clp_settings[] = {
  * @v clp_setting	Setting number, or 0 if not found
  */
 static unsigned int
-phantom_clp_setting ( struct phantom_nic *phantom, struct setting *setting ) {
+phantom_clp_setting ( struct phantom_nic *phantom,
+		      const struct setting *setting ) {
 	struct phantom_clp_setting *clp_setting;
 	unsigned int i;
 
@@ -1703,7 +1704,7 @@ phantom_clp_setting ( struct phantom_nic *phantom, struct setting *setting ) {
  * @ret applies		Setting applies within this settings block
  */
 static int phantom_setting_applies ( struct settings *settings,
-				     struct setting *setting ) {
+				     const struct setting *setting ) {
 	struct phantom_nic *phantom =
 		container_of ( settings, struct phantom_nic, settings );
 	unsigned int clp_setting;
@@ -1723,7 +1724,7 @@ static int phantom_setting_applies ( struct settings *settings,
  * @ret rc		Return status code
  */
 static int phantom_store_setting ( struct settings *settings,
-				   struct setting *setting,
+				   const struct setting *setting,
 				   const void *data, size_t len ) {
 	struct phantom_nic *phantom =
 		container_of ( settings, struct phantom_nic, settings );
diff --git a/src/hci/commands/nvo_cmd.c b/src/hci/commands/nvo_cmd.c
index 3fd684d0..e63dab08 100644
--- a/src/hci/commands/nvo_cmd.c
+++ b/src/hci/commands/nvo_cmd.c
@@ -58,8 +58,10 @@ static int show_exec ( int argc, char **argv ) {
 	struct show_options opts;
 	struct named_setting setting;
 	struct settings *origin;
+	struct setting fetched;
 	char name_buf[32];
 	char *value;
+	int len;
 	int rc;
 
 	/* Parse options */
@@ -71,19 +73,16 @@ static int show_exec ( int argc, char **argv ) {
 		goto err_parse_setting;
 
 	/* Fetch formatted setting value */
-	if ( ( rc = fetchf_setting_copy ( setting.settings, &setting.setting,
-					  &value ) ) < 0 ) {
+	if ( ( len = fetchf_setting_copy ( setting.settings, &setting.setting,
+					   &origin, &fetched, &value ) ) < 0 ) {
+		rc = len;
 		printf ( "Could not find \"%s\": %s\n",
 			 setting.setting.name, strerror ( rc ) );
 		goto err_fetchf;
 	}
 
-	/* Fetch origin and format fully-qualified name */
-	origin = fetch_setting_origin ( setting.settings, &setting.setting );
-	assert ( origin != NULL );
-	setting_name ( origin, &setting.setting, name_buf, sizeof ( name_buf ));
-
 	/* Print setting value */
+	setting_name ( origin, &fetched, name_buf, sizeof ( name_buf ) );
 	printf ( "%s = %s\n", name_buf, value );
 
 	/* Success */
@@ -234,7 +233,8 @@ static int read_value ( struct named_setting *setting, char **args __unused,
 	/* Read existing value, treating errors as equivalent to an
 	 * empty initial setting.
 	 */
-	fetchf_setting_copy ( setting->settings, &setting->setting, &existing );
+	fetchf_setting_copy ( setting->settings, &setting->setting,
+			      NULL, &setting->setting, &existing );
 
 	/* Read new value */
 	if ( ( rc = readline_history ( NULL, existing, NULL, value ) ) != 0 )
@@ -294,12 +294,11 @@ static int inc_exec ( int argc, char **argv ) {
 	     ( ( rc = parse_integer ( argv[ optind + 1 ], &increment ) ) != 0))
 		goto err_parse_increment;
 
-	/* Fetch existing setting value, if any, allowing for the fact
-	 * that numeric settings are big-endian and variable-length.
+	/* Read existing value, treating errors as equivalent to a
+	 * zero-valued :int32 initial setting.
 	 */
 	if ( ( rc = fetchn_setting ( setting.settings, &setting.setting,
-				     &value ) ) != 0 ) {
-		/* Treat as a non-existent :int32 setting with a zero value */
+				     NULL, &setting.setting, &value ) ) != 0 ) {
 		value = 0;
 		if ( ! setting.setting.type )
 			setting.setting.type = &setting_type_int32;
diff --git a/src/hci/commands/pci_cmd.c b/src/hci/commands/pci_cmd.c
index f2d69569..f5145fb3 100644
--- a/src/hci/commands/pci_cmd.c
+++ b/src/hci/commands/pci_cmd.c
@@ -68,8 +68,8 @@ static int pciscan_exec ( int argc, char **argv ) {
 		goto err_parse_setting;
 
 	/* Determine starting bus:dev.fn address */
-	if ( ( len = fetch_uint_setting ( setting.settings, &setting.setting,
-					  &prev ) ) < 0 ) {
+	if ( ( len = fetchn_setting ( setting.settings, &setting.setting,
+				      NULL, &setting.setting, &prev ) ) < 0 ) {
 		/* Setting not yet defined: start searching from 00:00.0 */
 		prev = 0;
 	} else {
diff --git a/src/hci/tui/settings_ui.c b/src/hci/tui/settings_ui.c
index 77ef8108..8fe13ad8 100644
--- a/src/hci/tui/settings_ui.c
+++ b/src/hci/tui/settings_ui.c
@@ -72,11 +72,16 @@ struct setting_row_widget {
 	 * Valid only for rows that lead to new settings blocks.
 	 */
 	struct settings *settings;
+	/** Configuration setting origin
+	 *
+	 * Valid only for rows that represent individual settings.
+	 */
+	struct settings *origin;
 	/** Configuration setting
 	 *
 	 * Valid only for rows that represent individual settings.
 	 */
-	struct setting *setting;
+	struct setting setting;
 	/** Screen row */
 	unsigned int row;
 	/** Screen column */
@@ -85,8 +90,6 @@ struct setting_row_widget {
 	struct edit_box editbox;
 	/** Editing in progress flag */
 	int editing;
-	/** Setting originates from this block flag */
-	int originates_here;
 	/** Buffer for setting's value */
 	char value[256]; /* enough size for a DHCP string */
 };
@@ -115,7 +118,6 @@ struct setting_widget {
 static unsigned int select_setting_row ( struct setting_widget *widget,
 					 unsigned int index ) {
 	struct settings *settings;
-	struct settings *origin;
 	struct setting *setting;
 	unsigned int count = 0;
 
@@ -147,18 +149,13 @@ static unsigned int select_setting_row ( struct setting_widget *widget,
 		if ( ! setting_applies ( widget->settings, setting ) )
 			continue;
 		if ( count++ == index ) {
-			widget->row.setting = setting;
 
-			/* Read current setting value */
-			fetchf_setting ( widget->settings, widget->row.setting,
+			/* Read current setting value and origin */
+			fetchf_setting ( widget->settings, setting,
+					 &widget->row.origin,
+					 &widget->row.setting,
 					 widget->row.value,
 					 sizeof ( widget->row.value ) );
-
-			/* Check setting's origin */
-			origin = fetch_setting_origin ( widget->settings,
-							widget->row.setting );
-			widget->row.originates_here =
-				( origin == widget->settings );
 		}
 	}
 
@@ -209,7 +206,7 @@ static void draw_setting_row ( struct setting_widget *widget ) {
 
 		/* Construct dot-padded name */
 		memset ( text.name, '.', sizeof ( text.name ) );
-		string_copy ( text.name, widget->row.setting->name,
+		string_copy ( text.name, widget->row.setting.name,
 			      sizeof ( text.name ) );
 
 		/* Construct space-padded value */
@@ -222,8 +219,10 @@ static void draw_setting_row ( struct setting_widget *widget ) {
 	}
 
 	/* Print row */
-	if ( widget->row.originates_here || widget->row.settings )
+	if ( ( widget->row.origin == widget->settings ) ||
+	     ( widget->row.settings != NULL ) ) {
 		attron ( A_BOLD );
+	}
 	mvprintw ( widget->row.row, widget->row.col, "%s", text.start );
 	attroff ( A_BOLD );
 	move ( widget->row.row, widget->row.col + curs_offset );
@@ -237,7 +236,7 @@ static void draw_setting_row ( struct setting_widget *widget ) {
  * @ret key		Key returned to application, or zero
  */
 static int edit_setting ( struct setting_widget *widget, int key ) {
-	assert ( widget->row.setting != NULL );
+	assert ( widget->row.setting.name != NULL );
 	widget->row.editing = 1;
 	return edit_editbox ( &widget->row.editbox, key );
 }
@@ -248,8 +247,8 @@ static int edit_setting ( struct setting_widget *widget, int key ) {
  * @v widget		Setting widget
  */
 static int save_setting ( struct setting_widget *widget ) {
-	assert ( widget->row.setting != NULL );
-	return storef_setting ( widget->settings, widget->row.setting,
+	assert ( widget->row.setting.name != NULL );
+	return storef_setting ( widget->settings, &widget->row.setting,
 				widget->row.value );
 }
 
@@ -344,28 +343,26 @@ static void draw_title_row ( struct setting_widget *widget ) {
  * @v widget		Setting widget
  */
 static void draw_info_row ( struct setting_widget *widget ) {
-	struct settings *origin;
 	char buf[32];
 
 	/* Draw nothing unless this row represents a setting */
 	clearmsg ( INFO_ROW );
 	clearmsg ( INFO_ROW + 1 );
-	if ( ! widget->row.setting )
+	if ( ! widget->row.setting.name )
 		return;
 
 	/* Determine a suitable setting name */
-	origin = fetch_setting_origin ( widget->settings, widget->row.setting );
-	if ( ! origin )
-		origin = widget->settings;
-	setting_name ( origin, widget->row.setting, buf, sizeof ( buf ) );
+	setting_name ( ( widget->row.origin ?
+			 widget->row.origin : widget->settings ),
+		       &widget->row.setting, buf, sizeof ( buf ) );
 
 	/* Draw row */
 	attron ( A_BOLD );
-	msg ( INFO_ROW, "%s - %s", buf, widget->row.setting->description );
+	msg ( INFO_ROW, "%s - %s", buf, widget->row.setting.description );
 	attroff ( A_BOLD );
 	color_set ( CPAIR_URL, NULL );
 	msg ( ( INFO_ROW + 1 ), "http://ipxe.org/cfg/%s",
-	      widget->row.setting->name );
+	      widget->row.setting.name );
 	color_set ( CPAIR_NORMAL, NULL );
 }
 
@@ -384,7 +381,7 @@ static void draw_instruction_row ( struct setting_widget *widget ) {
 	} else {
 		msg ( INSTRUCTION_ROW,
 		      "%sCtrl-X - exit configuration utility",
-		      ( widget->row.originates_here ?
+		      ( ( widget->row.origin == widget->settings ) ?
 			"Ctrl-D - delete setting" INSTRUCTION_PAD : "" ) );
 	}
 }
@@ -479,7 +476,7 @@ static int main_loop ( struct settings *settings ) {
 		if ( widget.row.editing ) {
 
 			/* Sanity check */
-			assert ( widget.row.setting != NULL );
+			assert ( widget.row.setting.name != NULL );
 
 			/* Redraw edit box */
 			color_set ( CPAIR_EDIT, NULL );
@@ -530,10 +527,10 @@ static int main_loop ( struct settings *settings ) {
 				move = +widget.num_rows;
 				break;
 			case CTRL_D:
-				if ( ! widget.row.setting )
+				if ( ! widget.row.setting.name )
 					break;
 				if ( ( rc = delete_setting ( widget.settings,
-						widget.row.setting ) ) != 0 ) {
+						&widget.row.setting ) ) != 0 ) {
 					alert ( " %s ", strerror ( rc ) );
 				}
 				select_setting_row ( &widget, widget.current );
@@ -550,7 +547,7 @@ static int main_loop ( struct settings *settings ) {
 				}
 				/* Fall through */
 			default:
-				if ( widget.row.setting ) {
+				if ( widget.row.setting.name ) {
 					edit_setting ( &widget, key );
 					redraw = 1;
 				}
diff --git a/src/include/ipxe/net80211.h b/src/include/ipxe/net80211.h
index dd8bd228..d752382a 100644
--- a/src/include/ipxe/net80211.h
+++ b/src/include/ipxe/net80211.h
@@ -1093,7 +1093,7 @@ struct net80211_wlan
 
 
 /** 802.11 encryption key setting */
-extern struct setting net80211_key_setting __setting ( SETTING_NETDEV_EXTRA );
+extern const struct setting net80211_key_setting __setting ( SETTING_NETDEV_EXTRA );
 
 
 /**
diff --git a/src/include/ipxe/nvo.h b/src/include/ipxe/nvo.h
index 487f8b3f..1a629da7 100644
--- a/src/include/ipxe/nvo.h
+++ b/src/include/ipxe/nvo.h
@@ -45,7 +45,8 @@ struct nvo_block {
 /** Name of non-volatile options settings block */
 #define NVO_SETTINGS_NAME "nvo"
 
-extern int nvo_applies ( struct settings *settings, struct setting *setting );
+extern int nvo_applies ( struct settings *settings,
+			 const struct setting *setting );
 extern void nvo_init ( struct nvo_block *nvo, struct nvs_device *nvs,
 		       size_t address, size_t len,
 		       int ( * resize ) ( struct nvo_block *nvo, size_t len ),
diff --git a/src/include/ipxe/settings.h b/src/include/ipxe/settings.h
index a6dfd210..25665ca7 100644
--- a/src/include/ipxe/settings.h
+++ b/src/include/ipxe/settings.h
@@ -32,7 +32,7 @@ struct setting {
 	 * This identifies the type of setting (e.g. string, IPv4
 	 * address, etc.).
 	 */
-	struct setting_type *type;
+	const struct setting_type *type;
 	/** Setting tag, if applicable
 	 *
 	 * The setting tag is a numerical description of the setting
@@ -45,7 +45,7 @@ struct setting {
 	 * For historic reasons, a NULL scope with a non-zero tag
 	 * indicates a DHCPv4 option setting.
 	 */
-	struct settings_scope *scope;
+	const struct settings_scope *scope;
 };
 
 /** Configuration setting table */
@@ -90,7 +90,7 @@ struct settings_operations {
 	 * @ret applies		Setting applies within this settings block
 	 */
 	int ( * applies ) ( struct settings *settings,
-			    struct setting *setting );
+			    const struct setting *setting );
 	/** Store value of setting
 	 *
 	 * @v settings		Settings block
@@ -99,7 +99,8 @@ struct settings_operations {
 	 * @v len		Length of setting data
 	 * @ret rc		Return status code
 	 */
-	int ( * store ) ( struct settings *settings, struct setting *setting,
+	int ( * store ) ( struct settings *settings,
+			  const struct setting *setting,
 			  const void *data, size_t len );
 	/** Fetch value of setting
 	 *
@@ -136,7 +137,7 @@ struct settings {
 	/** Settings block operations */
 	struct settings_operations *op;
 	/** Default scope for numerical settings constructed for this block */
-	struct settings_scope *default_scope;
+	const struct settings_scope *default_scope;
 };
 
 /**
@@ -193,7 +194,7 @@ struct setting_type {
 	 * @v len		Length of buffer
 	 * @ret len		Length of raw value, or negative error
 	 */
-	int ( * parse ) ( struct setting_type *type, const char *value,
+	int ( * parse ) ( const struct setting_type *type, const char *value,
 			  void *buf, size_t len );
 	/** Format setting value as a string
 	 *
@@ -204,7 +205,7 @@ struct setting_type {
 	 * @v len		Length of buffer
 	 * @ret len		Length of formatted value, or negative error
 	 */
-	int ( * format ) ( struct setting_type *type, const void *raw,
+	int ( * format ) ( const struct setting_type *type, const void *raw,
 			   size_t raw_len, char *buf, size_t len );
 	/** Convert number to setting value
 	 *
@@ -214,7 +215,8 @@ struct setting_type {
 	 * @v len		Length of buffer
 	 * @ret len		Length of raw value, or negative error
 	 */
-	int ( * denumerate ) ( struct setting_type *type, unsigned long value,
+	int ( * denumerate ) ( const struct setting_type *type,
+			       unsigned long value,
 			       void *buf, size_t len );
 	/** Convert setting value to number
 	 *
@@ -224,7 +226,7 @@ struct setting_type {
 	 * @v value		Numeric value to fill in
 	 * @ret rc		Return status code
 	 */
-	int ( * numerate ) ( struct setting_type *type, const void *raw,
+	int ( * numerate ) ( const struct setting_type *type, const void *raw,
 			     size_t raw_len, unsigned long *value );
 };
 
@@ -256,7 +258,7 @@ struct settings_applicator {
 /** A built-in setting */
 struct builtin_setting {
 	/** Setting */
-	struct setting *setting;
+	const struct setting *setting;
 	/** Fetch setting value
 	 *
 	 * @v data		Buffer to fill with setting data
@@ -273,7 +275,7 @@ struct builtin_setting {
 #define __builtin_setting __table_entry ( BUILTIN_SETTINGS, 01 )
 
 /** Built-in setting scope */
-extern struct settings_scope builtin_scope;
+extern const struct settings_scope builtin_scope;
 
 /**
  * A generic settings block
@@ -291,7 +293,7 @@ typedef struct settings * ( *get_child_settings_t ) ( struct settings *settings,
 						      const char *name );
 extern struct settings_operations generic_settings_operations;
 extern int generic_settings_store ( struct settings *settings,
-				    struct setting *setting,
+				    const struct setting *setting,
 				    const void *data, size_t len );
 extern int generic_settings_fetch ( struct settings *settings,
 				    struct setting *setting,
@@ -304,42 +306,50 @@ extern void unregister_settings ( struct settings *settings );
 
 extern struct settings * settings_target ( struct settings *settings );
 extern int setting_applies ( struct settings *settings,
-			     struct setting *setting );
-extern int store_setting ( struct settings *settings, struct setting *setting,
+			     const struct setting *setting );
+extern int store_setting ( struct settings *settings,
+			   const struct setting *setting,
 			   const void *data, size_t len );
-extern int fetch_setting ( struct settings *settings, struct setting *setting,
+extern int fetch_setting ( struct settings *settings,
+			   const struct setting *setting,
+			   struct settings **origin, struct setting *fetched,
 			   void *data, size_t len );
-extern struct settings * fetch_setting_origin ( struct settings *settings,
-						struct setting *setting );
-extern int fetch_setting_len ( struct settings *settings,
-			       struct setting *setting );
 extern int fetch_setting_copy ( struct settings *settings,
-				struct setting *setting, void **data );
+				const struct setting *setting,
+				struct settings **origin,
+				struct setting *fetched, void **data );
+extern int fetch_raw_setting ( struct settings *settings,
+			       const struct setting *setting,
+			       void *data, size_t len );
+extern int fetch_raw_setting_copy ( struct settings *settings,
+				    const struct setting *setting,
+				    void **data );
 extern int fetch_string_setting ( struct settings *settings,
-				  struct setting *setting,
+				  const struct setting *setting,
 				  char *data, size_t len );
 extern int fetch_string_setting_copy ( struct settings *settings,
-				       struct setting *setting,
+				       const struct setting *setting,
 				       char **data );
 extern int fetch_ipv4_array_setting ( struct settings *settings,
-				      struct setting *setting,
-				      struct in_addr *inp,
-				      unsigned int count );
+				      const struct setting *setting,
+				      struct in_addr *inp, unsigned int count );
 extern int fetch_ipv4_setting ( struct settings *settings,
-				struct setting *setting, struct in_addr *inp );
+				const struct setting *setting,
+				struct in_addr *inp );
 extern int fetch_int_setting ( struct settings *settings,
-			       struct setting *setting, long *value );
+			       const struct setting *setting, long *value );
 extern int fetch_uint_setting ( struct settings *settings,
-				struct setting *setting,
+				const struct setting *setting,
 				unsigned long *value );
 extern long fetch_intz_setting ( struct settings *settings,
-				 struct setting *setting );
+				 const struct setting *setting );
 extern unsigned long fetch_uintz_setting ( struct settings *settings,
-					   struct setting *setting );
+					   const struct setting *setting );
 extern int fetch_uuid_setting ( struct settings *settings,
-				struct setting *setting, union uuid *uuid );
+				const struct setting *setting,
+				union uuid *uuid );
 extern void clear_settings ( struct settings *settings );
-extern int setting_cmp ( struct setting *a, struct setting *b );
+extern int setting_cmp ( const struct setting *a, const struct setting *b );
 
 extern struct settings * find_child_settings ( struct settings *parent,
 					       const char *name );
@@ -351,61 +361,68 @@ extern struct setting * find_setting ( const char *name );
 extern int parse_setting_name ( char *name, get_child_settings_t get_child,
 				struct settings **settings,
 				struct setting *setting );
-extern int setting_name ( struct settings *settings, struct setting *setting,
+extern int setting_name ( struct settings *settings,
+			  const struct setting *setting,
 			  char *buf, size_t len );
-extern int setting_format ( struct setting_type *type, const void *raw,
+extern int setting_format ( const struct setting_type *type, const void *raw,
 			    size_t raw_len, char *buf, size_t len );
-extern int setting_parse ( struct setting_type *type, const char *value,
+extern int setting_parse ( const struct setting_type *type, const char *value,
 			   void *buf, size_t len );
-extern int setting_numerate ( struct setting_type *type, const void *raw,
+extern int setting_numerate ( const struct setting_type *type, const void *raw,
 			      size_t raw_len, unsigned long *value );
-extern int setting_denumerate ( struct setting_type *type, unsigned long value,
-				void *buf, size_t len );
-extern int fetchf_setting ( struct settings *settings, struct setting *setting,
+extern int setting_denumerate ( const struct setting_type *type,
+				unsigned long value, void *buf, size_t len );
+extern int fetchf_setting ( struct settings *settings,
+			    const struct setting *setting,
+			    struct settings **origin, struct setting *fetched,
 			    char *buf, size_t len );
 extern int fetchf_setting_copy ( struct settings *settings,
-				 struct setting *setting, char **value );
+				 const struct setting *setting,
+				 struct settings **origin,
+				 struct setting *fetched, char **value );
 extern int storef_setting ( struct settings *settings,
-			    struct setting *setting,
-			    const char *value );
-extern int fetchn_setting ( struct settings *settings, struct setting *setting,
+			    const struct setting *setting, const char *value );
+extern int fetchn_setting ( struct settings *settings,
+			    const struct setting *setting,
+			    struct settings **origin, struct setting *fetched,
 			    unsigned long *value );
-extern int storen_setting ( struct settings *settings, struct setting *setting,
+extern int storen_setting ( struct settings *settings,
+			    const struct setting *setting,
 			    unsigned long value );
 extern char * expand_settings ( const char *string );
 
-extern struct setting_type setting_type_string __setting_type;
-extern struct setting_type setting_type_uristring __setting_type;
-extern struct setting_type setting_type_ipv4 __setting_type;
-extern struct setting_type setting_type_ipv6 __setting_type;
-extern struct setting_type setting_type_int8 __setting_type;
-extern struct setting_type setting_type_int16 __setting_type;
-extern struct setting_type setting_type_int32 __setting_type;
-extern struct setting_type setting_type_uint8 __setting_type;
-extern struct setting_type setting_type_uint16 __setting_type;
-extern struct setting_type setting_type_uint32 __setting_type;
-extern struct setting_type setting_type_hex __setting_type;
-extern struct setting_type setting_type_hexhyp __setting_type;
-extern struct setting_type setting_type_hexraw __setting_type;
-extern struct setting_type setting_type_uuid __setting_type;
-extern struct setting_type setting_type_busdevfn __setting_type;
-
-extern struct setting ip_setting __setting ( SETTING_IPv4 );
-extern struct setting netmask_setting __setting ( SETTING_IPv4 );
-extern struct setting gateway_setting __setting ( SETTING_IPv4 );
-extern struct setting dns_setting __setting ( SETTING_IPv4_EXTRA );
-extern struct setting hostname_setting __setting ( SETTING_HOST );
-extern struct setting domain_setting __setting ( SETTING_IPv4_EXTRA );
-extern struct setting filename_setting __setting ( SETTING_BOOT );
-extern struct setting root_path_setting __setting ( SETTING_SANBOOT );
-extern struct setting username_setting __setting ( SETTING_AUTH );
-extern struct setting password_setting __setting ( SETTING_AUTH );
-extern struct setting priority_setting __setting ( SETTING_MISC );
-extern struct setting uuid_setting __setting ( SETTING_HOST );
-extern struct setting next_server_setting __setting ( SETTING_BOOT );
-extern struct setting mac_setting __setting ( SETTING_NETDEV );
-extern struct setting busid_setting __setting ( SETTING_NETDEV );
-extern struct setting user_class_setting __setting ( SETTING_HOST_EXTRA );
+extern const struct setting_type setting_type_string __setting_type;
+extern const struct setting_type setting_type_uristring __setting_type;
+extern const struct setting_type setting_type_ipv4 __setting_type;
+extern const struct setting_type setting_type_ipv6 __setting_type;
+extern const struct setting_type setting_type_int8 __setting_type;
+extern const struct setting_type setting_type_int16 __setting_type;
+extern const struct setting_type setting_type_int32 __setting_type;
+extern const struct setting_type setting_type_uint8 __setting_type;
+extern const struct setting_type setting_type_uint16 __setting_type;
+extern const struct setting_type setting_type_uint32 __setting_type;
+extern const struct setting_type setting_type_hex __setting_type;
+extern const struct setting_type setting_type_hexhyp __setting_type;
+extern const struct setting_type setting_type_hexraw __setting_type;
+extern const struct setting_type setting_type_uuid __setting_type;
+extern const struct setting_type setting_type_busdevfn __setting_type;
+
+extern const struct setting ip_setting __setting ( SETTING_IPv4 );
+extern const struct setting netmask_setting __setting ( SETTING_IPv4 );
+extern const struct setting gateway_setting __setting ( SETTING_IPv4 );
+extern const struct setting dns_setting __setting ( SETTING_IPv4_EXTRA );
+extern const struct setting hostname_setting __setting ( SETTING_HOST );
+extern const struct setting domain_setting __setting ( SETTING_IPv4_EXTRA );
+extern const struct setting filename_setting __setting ( SETTING_BOOT );
+extern const struct setting root_path_setting __setting ( SETTING_SANBOOT );
+extern const struct setting username_setting __setting ( SETTING_AUTH );
+extern const struct setting password_setting __setting ( SETTING_AUTH );
+extern const struct setting priority_setting __setting ( SETTING_MISC );
+extern const struct setting uuid_setting __setting ( SETTING_HOST );
+extern const struct setting next_server_setting __setting ( SETTING_BOOT );
+extern const struct setting mac_setting __setting ( SETTING_NETDEV );
+extern const struct setting busid_setting __setting ( SETTING_NETDEV );
+extern const struct setting user_class_setting __setting ( SETTING_HOST_EXTRA );
 
 /**
  * Initialise a settings block
@@ -418,7 +435,7 @@ extern struct setting user_class_setting __setting ( SETTING_HOST_EXTRA );
 static inline void settings_init ( struct settings *settings,
 				   struct settings_operations *op,
 				   struct refcnt *refcnt,
-				   struct settings_scope *default_scope ) {
+				   const struct settings_scope *default_scope ){
 	INIT_LIST_HEAD ( &settings->siblings );
 	INIT_LIST_HEAD ( &settings->children );
 	settings->op = op;
@@ -447,20 +464,21 @@ static inline void generic_settings_init ( struct generic_settings *generics,
  * @ret rc		Return status code
  */
 static inline int delete_setting ( struct settings *settings,
-				   struct setting *setting ) {
+				   const struct setting *setting ) {
 	return store_setting ( settings, setting, NULL, 0 );
 }
 
 /**
- * Check existence of setting
+ * Check existence of predefined setting
  *
  * @v settings		Settings block, or NULL to search all blocks
  * @v setting		Setting to fetch
  * @ret exists		Setting exists
  */
 static inline int setting_exists ( struct settings *settings,
-				   struct setting *setting ) {
-	return ( fetch_setting_len ( settings, setting ) >= 0 );
+				   const struct setting *setting ) {
+	return ( fetch_setting ( settings, setting, NULL, NULL,
+				 NULL, 0 ) >= 0 );
 }
 
 #endif /* _IPXE_SETTINGS_H */
diff --git a/src/interface/efi/efi_snp_hii.c b/src/interface/efi/efi_snp_hii.c
index 9ea15a62..61954b63 100644
--- a/src/interface/efi/efi_snp_hii.c
+++ b/src/interface/efi/efi_snp_hii.c
@@ -276,7 +276,9 @@ static int efi_snp_hii_fetch ( struct efi_snp_device *snpdev,
 			       const char *key, const char *value,
 			       wchar_t **results, int *have_setting ) {
 	struct settings *settings = efi_snp_hii_settings ( snpdev );
+	struct settings *origin;
 	struct setting *setting;
+	struct setting fetched;
 	int len;
 	char *buf;
 	char *encoded;
@@ -311,7 +313,8 @@ static int efi_snp_hii_fetch ( struct efi_snp_device *snpdev,
 	if ( setting_exists ( settings, setting ) ) {
 
 		/* Calculate formatted length */
-		len = fetchf_setting ( settings, setting, NULL, 0 );
+		len = fetchf_setting ( settings, setting, &origin, &fetched,
+				       NULL, 0 );
 		if ( len < 0 ) {
 			rc = len;
 			DBGC ( snpdev, "SNPDEV %p could not fetch %s: %s\n",
@@ -328,7 +331,8 @@ static int efi_snp_hii_fetch ( struct efi_snp_device *snpdev,
 		encoded = ( buf + len + 1 /* NUL */ );
 
 		/* Format value */
-		fetchf_setting ( settings, setting, buf, ( len + 1 /* NUL */ ));
+		fetchf_setting ( origin, &fetched, NULL, NULL, buf,
+				 ( len + 1 /* NUL */ ) );
 		for ( i = 0 ; i < len ; i++ ) {
 			sprintf ( ( encoded + ( 4 * i ) ), "%04x",
 				  *( ( uint8_t * ) buf + i ) );
diff --git a/src/interface/smbios/smbios_settings.c b/src/interface/smbios/smbios_settings.c
index ecd3f1d9..9995bd75 100644
--- a/src/interface/smbios/smbios_settings.c
+++ b/src/interface/smbios/smbios_settings.c
@@ -28,7 +28,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #include <ipxe/smbios.h>
 
 /** SMBIOS settings scope */
-static struct settings_scope smbios_settings_scope;
+static const struct settings_scope smbios_settings_scope;
 
 /**
  * Construct SMBIOS raw-data tag
@@ -63,7 +63,7 @@ static struct settings_scope smbios_settings_scope;
  * @ret applies		Setting applies within this settings block
  */
 static int smbios_applies ( struct settings *settings __unused,
-			    struct setting *setting ) {
+			    const struct setting *setting ) {
 
 	return ( setting->scope == &smbios_settings_scope );
 }
@@ -188,7 +188,7 @@ struct init_fn smbios_init_fn __init_fn ( INIT_NORMAL ) = {
 };
 
 /** UUID setting obtained via SMBIOS */
-struct setting uuid_setting __setting ( SETTING_HOST ) = {
+const struct setting uuid_setting __setting ( SETTING_HOST ) = {
 	.name = "uuid",
 	.description = "UUID",
 	.tag = SMBIOS_RAW_TAG ( SMBIOS_TYPE_SYSTEM_INFORMATION,
@@ -198,7 +198,7 @@ struct setting uuid_setting __setting ( SETTING_HOST ) = {
 };
 
 /** Other SMBIOS predefined settings */
-struct setting smbios_predefined_settings[] __setting ( SETTING_HOST_EXTRA ) = {
+const struct setting smbios_predefined_settings[] __setting ( SETTING_HOST_EXTRA ) = {
 	{
 		.name = "manufacturer",
 		.description = "Manufacturer",
diff --git a/src/net/80211/net80211.c b/src/net/80211/net80211.c
index 3893f652..db4dc116 100644
--- a/src/net/80211/net80211.c
+++ b/src/net/80211/net80211.c
@@ -204,7 +204,7 @@ struct settings_applicator net80211_applicator __settings_applicator = {
  * If this is blank, we scan for all networks and use the one with the
  * greatest signal strength.
  */
-struct setting net80211_ssid_setting __setting ( SETTING_NETDEV_EXTRA ) = {
+const struct setting net80211_ssid_setting __setting ( SETTING_NETDEV_EXTRA ) = {
 	.name = "ssid",
 	.description = "Wireless SSID",
 	.type = &setting_type_string,
@@ -216,7 +216,7 @@ struct setting net80211_ssid_setting __setting ( SETTING_NETDEV_EXTRA ) = {
  * active scan (send probe packets). If this setting is nonzero, an
  * active scan on the 2.4GHz band will be used to associate.
  */
-struct setting net80211_active_setting __setting ( SETTING_NETDEV_EXTRA ) = {
+const struct setting net80211_active_setting __setting ( SETTING_NETDEV_EXTRA ) = {
 	.name = "active-scan",
 	.description = "Actively scan for wireless networks",
 	.type = &setting_type_int8,
@@ -228,7 +228,7 @@ struct setting net80211_active_setting __setting ( SETTING_NETDEV_EXTRA ) = {
  * normal iPXE method for entering hex settings; an ASCII string of
  * hex characters will not behave as expected.
  */
-struct setting net80211_key_setting __setting ( SETTING_NETDEV_EXTRA ) = {
+const struct setting net80211_key_setting __setting ( SETTING_NETDEV_EXTRA ) = {
 	.name = "key",
 	.description = "Wireless encryption key",
 	.type = &setting_type_string,
diff --git a/src/net/80211/wep.c b/src/net/80211/wep.c
index 37b27f71..e22ac899 100644
--- a/src/net/80211/wep.c
+++ b/src/net/80211/wep.c
@@ -236,8 +236,8 @@ static int trivial_init ( struct net80211_device *dev )
 	     dev->associating->crypto == NET80211_CRYPT_NONE )
 		return 0;	/* no crypto? OK. */
 
-	len = fetch_setting ( netdev_settings ( dev->netdev ),
-			      &net80211_key_setting, key, WEP_MAX_KEY );
+	len = fetch_raw_setting ( netdev_settings ( dev->netdev ),
+				  &net80211_key_setting, key, WEP_MAX_KEY );
 
 	if ( len <= 0 ) {
 		DBGC ( dev, "802.11 %p cannot do WEP without a key\n", dev );
@@ -278,8 +278,8 @@ static int trivial_change_key ( struct net80211_device *dev )
 	if ( ! dev->crypto || ( dev->crypto->init != wep_init ) )
 		change ^= 1;
 
-	len = fetch_setting ( netdev_settings ( dev->netdev ),
-			      &net80211_key_setting, key, WEP_MAX_KEY );
+	len = fetch_raw_setting ( netdev_settings ( dev->netdev ),
+				  &net80211_key_setting, key, WEP_MAX_KEY );
 	if ( len <= 0 )
 		change ^= 1;
 
diff --git a/src/net/dhcppkt.c b/src/net/dhcppkt.c
index 3722c09e..a9a6d3a9 100644
--- a/src/net/dhcppkt.c
+++ b/src/net/dhcppkt.c
@@ -226,7 +226,7 @@ int dhcppkt_fetch ( struct dhcp_packet *dhcppkt, unsigned int tag,
  * @ret applies		Setting applies within this settings block
  */
 static int dhcppkt_settings_applies ( struct settings *settings,
-				      struct setting *setting ) {
+				      const struct setting *setting ) {
 	struct dhcp_packet *dhcppkt =
 		container_of ( settings, struct dhcp_packet, settings );
 
@@ -244,7 +244,7 @@ static int dhcppkt_settings_applies ( struct settings *settings,
  * @ret rc		Return status code
  */
 static int dhcppkt_settings_store ( struct settings *settings,
-				    struct setting *setting,
+				    const struct setting *setting,
 				    const void *data, size_t len ) {
 	struct dhcp_packet *dhcppkt =
 		container_of ( settings, struct dhcp_packet, settings );
diff --git a/src/net/fakedhcp.c b/src/net/fakedhcp.c
index d67501ed..3dec88b1 100644
--- a/src/net/fakedhcp.c
+++ b/src/net/fakedhcp.c
@@ -49,8 +49,8 @@ static int copy_encap_settings ( struct dhcp_packet *dest,
 	struct setting setting = { .name = "" };
 	unsigned int subtag;
 	unsigned int tag;
+	void *data;
 	int len;
-	int check_len;
 	int rc;
 
 	for ( subtag = DHCP_MIN_OPTION; subtag <= DHCP_MAX_OPTION; subtag++ ) {
@@ -66,17 +66,11 @@ static int copy_encap_settings ( struct dhcp_packet *dest,
 		default:
 			/* Copy setting, if present */
 			setting.tag = tag;
-			len = fetch_setting_len ( source, &setting );
-			if ( len < 0 )
-				break;
-			{
-				char buf[len];
-
-				check_len = fetch_setting ( source, &setting,
-							    buf, sizeof (buf));
-				assert ( check_len == len );
-				if ( ( rc = dhcppkt_store ( dest, tag, buf,
-							    sizeof(buf) )) !=0)
+			len = fetch_raw_setting_copy ( source, &setting, &data);
+			if ( len >= 0 ) {
+				rc = dhcppkt_store ( dest, tag, data, len );
+				free ( data );
+				if ( rc != 0 )
 					return rc;
 			}
 			break;
diff --git a/src/net/ipv4.c b/src/net/ipv4.c
index 438fe9ac..f0a2e4d6 100644
--- a/src/net/ipv4.c
+++ b/src/net/ipv4.c
@@ -591,7 +591,7 @@ struct sockaddr_converter ipv4_sockaddr_converter __sockaddr_converter = {
  */
 
 /** IPv4 address setting */
-struct setting ip_setting __setting ( SETTING_IPv4 ) = {
+const struct setting ip_setting __setting ( SETTING_IPv4 ) = {
 	.name = "ip",
 	.description = "IP address",
 	.tag = DHCP_EB_YIADDR,
@@ -599,7 +599,7 @@ struct setting ip_setting __setting ( SETTING_IPv4 ) = {
 };
 
 /** IPv4 subnet mask setting */
-struct setting netmask_setting __setting ( SETTING_IPv4 ) = {
+const struct setting netmask_setting __setting ( SETTING_IPv4 ) = {
 	.name = "netmask",
 	.description = "Subnet mask",
 	.tag = DHCP_SUBNET_MASK,
@@ -607,7 +607,7 @@ struct setting netmask_setting __setting ( SETTING_IPv4 ) = {
 };
 
 /** Default gateway setting */
-struct setting gateway_setting __setting ( SETTING_IPv4 ) = {
+const struct setting gateway_setting __setting ( SETTING_IPv4 ) = {
 	.name = "gateway",
 	.description = "Default gateway",
 	.tag = DHCP_ROUTERS,
diff --git a/src/net/ipv6.c b/src/net/ipv6.c
index b4f33f0d..68a0c89b 100644
--- a/src/net/ipv6.c
+++ b/src/net/ipv6.c
@@ -954,7 +954,7 @@ struct sockaddr_converter ipv6_sockaddr_converter __sockaddr_converter = {
  * @v len		Length of buffer
  * @ret len		Length of raw value, or negative error
  */
-static int parse_ipv6_setting ( struct setting_type *type __unused,
+static int parse_ipv6_setting ( const struct setting_type *type __unused,
 				const char *value, void *buf, size_t len ) {
 	struct in6_addr ipv6;
 	int rc;
@@ -981,7 +981,7 @@ static int parse_ipv6_setting ( struct setting_type *type __unused,
  * @v len		Length of buffer
  * @ret len		Length of formatted value, or negative error
  */
-static int format_ipv6_setting ( struct setting_type *type __unused,
+static int format_ipv6_setting ( const struct setting_type *type __unused,
 				 const void *raw, size_t raw_len, char *buf,
 				 size_t len ) {
 	const struct in6_addr *ipv6 = raw;
@@ -992,7 +992,7 @@ static int format_ipv6_setting ( struct setting_type *type __unused,
 }
 
 /** An IPv6 address setting type */
-struct setting_type setting_type_ipv6 __setting_type = {
+const struct setting_type setting_type_ipv6 __setting_type = {
 	.name = "ipv6",
 	.parse = parse_ipv6_setting,
 	.format = format_ipv6_setting,
diff --git a/src/net/netdev_settings.c b/src/net/netdev_settings.c
index 994e0506..cfadd9e4 100644
--- a/src/net/netdev_settings.c
+++ b/src/net/netdev_settings.c
@@ -36,27 +36,27 @@ FILE_LICENCE ( GPL2_OR_LATER );
  */
 
 /** Network device predefined settings */
-struct setting mac_setting __setting ( SETTING_NETDEV ) = {
+const struct setting mac_setting __setting ( SETTING_NETDEV ) = {
 	.name = "mac",
 	.description = "MAC address",
 	.type = &setting_type_hex,
 };
-struct setting bustype_setting __setting ( SETTING_NETDEV ) = {
+const struct setting bustype_setting __setting ( SETTING_NETDEV ) = {
 	.name = "bustype",
 	.description = "Bus type",
 	.type = &setting_type_string,
 };
-struct setting busloc_setting __setting ( SETTING_NETDEV ) = {
+const struct setting busloc_setting __setting ( SETTING_NETDEV ) = {
 	.name = "busloc",
 	.description = "Bus location",
 	.type = &setting_type_uint32,
 };
-struct setting busid_setting __setting ( SETTING_NETDEV ) = {
+const struct setting busid_setting __setting ( SETTING_NETDEV ) = {
 	.name = "busid",
 	.description = "Bus ID",
 	.type = &setting_type_hex,
 };
-struct setting chip_setting __setting ( SETTING_NETDEV ) = {
+const struct setting chip_setting __setting ( SETTING_NETDEV ) = {
 	.name = "chip",
 	.description = "Chip",
 	.type = &setting_type_string,
@@ -194,7 +194,7 @@ static int netdev_fetch_chip ( struct net_device *netdev, void *data,
 /** A network device setting operation */
 struct netdev_setting_operation {
 	/** Setting */
-	struct setting *setting;
+	const struct setting *setting;
 	/** Store setting (or NULL if not supported)
 	 *
 	 * @v netdev		Network device
@@ -232,7 +232,8 @@ static struct netdev_setting_operation netdev_setting_operations[] = {
  * @v len		Length of setting data
  * @ret rc		Return status code
  */
-static int netdev_store ( struct settings *settings, struct setting *setting,
+static int netdev_store ( struct settings *settings,
+			  const struct setting *setting,
 			  const void *data, size_t len ) {
 	struct net_device *netdev = container_of ( settings, struct net_device,
 						   settings.settings );
diff --git a/src/net/tcp/iscsi.c b/src/net/tcp/iscsi.c
index c9daf1ff..197069cc 100644
--- a/src/net/tcp/iscsi.c
+++ b/src/net/tcp/iscsi.c
@@ -1860,7 +1860,7 @@ enum iscsi_root_path_component {
 };
 
 /** iSCSI initiator IQN setting */
-struct setting initiator_iqn_setting __setting ( SETTING_SANBOOT_EXTRA ) = {
+const struct setting initiator_iqn_setting __setting ( SETTING_SANBOOT_EXTRA ) = {
 	.name = "initiator-iqn",
 	.description = "iSCSI initiator name",
 	.tag = DHCP_ISCSI_INITIATOR_IQN,
@@ -1868,7 +1868,7 @@ struct setting initiator_iqn_setting __setting ( SETTING_SANBOOT_EXTRA ) = {
 };
 
 /** iSCSI reverse username setting */
-struct setting reverse_username_setting __setting ( SETTING_AUTH_EXTRA ) = {
+const struct setting reverse_username_setting __setting ( SETTING_AUTH_EXTRA ) = {
 	.name = "reverse-username",
 	.description = "Reverse user name",
 	.tag = DHCP_EB_REVERSE_USERNAME,
@@ -1876,7 +1876,7 @@ struct setting reverse_username_setting __setting ( SETTING_AUTH_EXTRA ) = {
 };
 
 /** iSCSI reverse password setting */
-struct setting reverse_password_setting __setting ( SETTING_AUTH_EXTRA ) = {
+const struct setting reverse_password_setting __setting ( SETTING_AUTH_EXTRA ) = {
 	.name = "reverse-password",
 	.description = "Reverse password",
 	.tag = DHCP_EB_REVERSE_PASSWORD,
@@ -1947,46 +1947,23 @@ static int iscsi_fetch_settings ( struct iscsi_session *iscsi ) {
 	/* Fetch relevant settings.  Don't worry about freeing on
 	 * error, since iscsi_free() will take care of that anyway.
 	 */
-	if ( ( len = fetch_string_setting_copy ( NULL, &username_setting,
-					  &iscsi->initiator_username ) ) < 0 ) {
-		DBGC ( iscsi, "iSCSI %p could not fetch username: %s\n",
-		       iscsi, strerror ( len ) );
-		return len;
-	}
-	if ( ( len = fetch_string_setting_copy ( NULL, &password_setting,
-					  &iscsi->initiator_password ) ) < 0 ) {
-		DBGC ( iscsi, "iSCSI %p could not fetch password: %s\n",
-		       iscsi, strerror ( len ) );
-		return len;
-	}
-	if ( ( len = fetch_string_setting_copy( NULL, &reverse_username_setting,
-					     &iscsi->target_username ) ) < 0 ) {
-		DBGC ( iscsi, "iSCSI %p could not fetch reverse username: %s\n",
-		       iscsi, strerror ( len ) );
-		return len;
-	}
-	if ( ( len = fetch_string_setting_copy( NULL, &reverse_password_setting,
-					     &iscsi->target_password ) ) < 0 ) {
-		DBGC ( iscsi, "iSCSI %p could not fetch reverse password: %s\n",
-		       iscsi, strerror ( len ) );
-		return len;
-	}
-
-	/* Find a suitable initiator name */
-	if ( ( len = fetch_string_setting_copy ( NULL, &initiator_iqn_setting,
-					       &iscsi->initiator_iqn ) ) < 0 ) {
-		DBGC ( iscsi, "iSCSI %p could not fetch initiator IQN: %s\n",
-		       iscsi, strerror ( len ) );
-		return len;
-	}
+	fetch_string_setting_copy ( NULL, &username_setting,
+				    &iscsi->initiator_username );
+	fetch_string_setting_copy ( NULL, &password_setting,
+				    &iscsi->initiator_password );
+	fetch_string_setting_copy ( NULL, &reverse_username_setting,
+				    &iscsi->target_username );
+	fetch_string_setting_copy ( NULL, &reverse_password_setting,
+				    &iscsi->target_password );
+
+	/* Use explicit initiator IQN if provided */
+	fetch_string_setting_copy ( NULL, &initiator_iqn_setting,
+				    &iscsi->initiator_iqn );
 	if ( iscsi->initiator_iqn )
 		return 0;
-	if ( ( len = fetch_string_setting_copy ( NULL, &hostname_setting,
-						&hostname ) ) < 0 ) {
-		DBGC ( iscsi, "iSCSI %p could not fetch hostname: %s\n",
-		       iscsi, strerror ( len ) );
-		return len;
-	}
+
+	/* Otherwise, try to construct an initiator IQN from the hostname */
+	fetch_string_setting_copy ( NULL, &hostname_setting, &hostname );
 	if ( hostname ) {
 		len = asprintf ( &iscsi->initiator_iqn,
 				 ISCSI_DEFAULT_IQN_PREFIX ":%s", hostname );
@@ -1999,6 +1976,8 @@ static int iscsi_fetch_settings ( struct iscsi_session *iscsi ) {
 		assert ( iscsi->initiator_iqn );
 		return 0;
 	}
+
+	/* Otherwise, try to construct an initiator IQN from the UUID */
 	if ( ( len = fetch_uuid_setting ( NULL, &uuid_setting, &uuid ) ) < 0 ) {
 		DBGC ( iscsi, "iSCSI %p has no suitable initiator IQN\n",
 		       iscsi );
diff --git a/src/net/tcp/oncrpc.c b/src/net/tcp/oncrpc.c
index 819d3179..0a3b3858 100644
--- a/src/net/tcp/oncrpc.c
+++ b/src/net/tcp/oncrpc.c
@@ -58,14 +58,14 @@ struct oncrpc_cred oncrpc_auth_none = {
 	.length = 0
 };
 
-struct setting uid_setting __setting ( SETTING_AUTH ) = {
+const struct setting uid_setting __setting ( SETTING_AUTH ) = {
 	.name        = "uid",
 	.description = "User ID",
 	.tag         = DHCP_EB_UID,
 	.type        = &setting_type_uint32
 };
 
-struct setting gid_setting __setting ( SETTING_AUTH ) = {
+const struct setting gid_setting __setting ( SETTING_AUTH ) = {
 	.name        = "gid",
 	.description = "Group ID",
 	.tag         = DHCP_EB_GID,
diff --git a/src/net/tcp/syslogs.c b/src/net/tcp/syslogs.c
index bcda8b45..503ed177 100644
--- a/src/net/tcp/syslogs.c
+++ b/src/net/tcp/syslogs.c
@@ -190,7 +190,7 @@ struct console_driver syslogs_console __console_driver = {
  */
 
 /** Encrypted syslog server setting */
-struct setting syslogs_setting __setting ( SETTING_MISC ) = {
+const struct setting syslogs_setting __setting ( SETTING_MISC ) = {
 	.name = "syslogs",
 	.description = "Encrypted syslog server",
 	.tag = DHCP_EB_SYSLOGS_SERVER,
@@ -206,15 +206,10 @@ static int apply_syslogs_settings ( void ) {
 	static char *old_server;
 	char *server;
 	struct interface *socket;
-	int len;
 	int rc;
 
 	/* Fetch log server */
-	len = fetch_string_setting_copy ( NULL, &syslogs_setting, &server );
-	if ( len < 0 ) {
-		rc = len;
-		goto err_fetch_server;
-	}
+	fetch_string_setting_copy ( NULL, &syslogs_setting, &server );
 
 	/* Do nothing unless log server has changed */
 	if ( ( ( server == NULL ) && ( old_server == NULL ) ) ||
@@ -266,7 +261,6 @@ static int apply_syslogs_settings ( void ) {
  out_no_server:
  out_no_change:
 	free ( server );
- err_fetch_server:
 	return rc;
 }
 
diff --git a/src/net/udp/dhcp.c b/src/net/udp/dhcp.c
index 66bcc83a..3163f39c 100644
--- a/src/net/udp/dhcp.c
+++ b/src/net/udp/dhcp.c
@@ -92,7 +92,7 @@ static uint8_t dhcp_request_options_data[] = {
 };
 
 /** DHCP server address setting */
-struct setting dhcp_server_setting __setting ( SETTING_MISC ) = {
+const struct setting dhcp_server_setting __setting ( SETTING_MISC ) = {
 	.name = "dhcp-server",
 	.description = "DHCP server",
 	.tag = DHCP_SERVER_IDENTIFIER,
@@ -975,6 +975,7 @@ int dhcp_create_request ( struct dhcp_packet *dhcppkt,
 	uint8_t *dhcp_features;
 	size_t dhcp_features_len;
 	size_t ll_addr_len;
+	void *user_class;
 	ssize_t len;
 	int rc;
 
@@ -985,7 +986,7 @@ int dhcp_create_request ( struct dhcp_packet *dhcppkt,
 					 data, max_len ) ) != 0 ) {
 		DBG ( "DHCP could not create DHCP packet: %s\n",
 		      strerror ( rc ) );
-		return rc;
+		goto err_create_packet;
 	}
 
 	/* Set client IP address */
@@ -998,17 +999,17 @@ int dhcp_create_request ( struct dhcp_packet *dhcppkt,
 				    dhcp_features_len ) ) != 0 ) {
 		DBG ( "DHCP could not set features list option: %s\n",
 		      strerror ( rc ) );
-		return rc;
+		goto err_store_features;
 	}
 
 	/* Add options to identify the network device */
-	fetch_setting ( &netdev->settings.settings, &busid_setting, &dhcp_desc,
-		sizeof ( dhcp_desc ) );
+	fetch_raw_setting ( netdev_settings ( netdev ), &busid_setting,
+			    &dhcp_desc, sizeof ( dhcp_desc ) );
 	if ( ( rc = dhcppkt_store ( dhcppkt, DHCP_EB_BUS_ID, &dhcp_desc,
 				    sizeof ( dhcp_desc ) ) ) != 0 ) {
 		DBG ( "DHCP could not set bus ID option: %s\n",
 		      strerror ( rc ) );
-		return rc;
+		goto err_store_busid;
 	}
 
 	/* Add DHCP client identifier.  Required for Infiniband, and
@@ -1022,7 +1023,7 @@ int dhcp_create_request ( struct dhcp_packet *dhcppkt,
 				    ( ll_addr_len + 1 ) ) ) != 0 ) {
 		DBG ( "DHCP could not set client ID: %s\n",
 		      strerror ( rc ) );
-		return rc;
+		goto err_store_client_id;
 	}
 
 	/* Add client UUID, if we have one.  Required for PXE.  The
@@ -1039,25 +1040,29 @@ int dhcp_create_request ( struct dhcp_packet *dhcppkt,
 					    sizeof ( client_uuid ) ) ) != 0 ) {
 			DBG ( "DHCP could not set client UUID: %s\n",
 			      strerror ( rc ) );
-			return rc;
+			goto err_store_client_uuid;
 		}
 	}
 
 	/* Add user class, if we have one. */
-	if ( ( len = fetch_setting_len ( NULL, &user_class_setting ) ) >= 0 ) {
-		char user_class[len];
-		fetch_setting ( NULL, &user_class_setting, user_class,
-				sizeof ( user_class ) );
+	if ( ( len = fetch_raw_setting_copy ( NULL, &user_class_setting,
+					      &user_class ) ) >= 0 ) {
 		if ( ( rc = dhcppkt_store ( dhcppkt, DHCP_USER_CLASS_ID,
-					    &user_class,
-					    sizeof ( user_class ) ) ) != 0 ) {
+					    user_class, len ) ) != 0 ) {
 			DBG ( "DHCP could not set user class: %s\n",
 			      strerror ( rc ) );
-			return rc;
+			goto err_store_user_class;
 		}
 	}
 
-	return 0;
+ err_store_user_class:
+	free ( user_class );
+ err_store_client_uuid:
+ err_store_client_id:
+ err_store_busid:
+ err_store_features:
+ err_create_packet:
+	return rc;
 }
 
 /****************************************************************************
@@ -1384,7 +1389,8 @@ int start_pxebs ( struct interface *job, struct net_device *netdev,
 	int rc;
 
 	/* Get upper bound for PXE boot server IP address list */
-	pxebs_list_len = fetch_setting_len ( NULL, &pxe_boot_servers_setting );
+	pxebs_list_len = fetch_raw_setting ( NULL, &pxe_boot_servers_setting,
+					     NULL, 0 );
 	if ( pxebs_list_len < 0 )
 		pxebs_list_len = 0;
 
@@ -1422,8 +1428,8 @@ int start_pxebs ( struct interface *job, struct net_device *netdev,
 	if ( pxebs_list_len ) {
 		uint8_t buf[pxebs_list_len];
 
-		fetch_setting ( NULL, &pxe_boot_servers_setting,
-				buf, sizeof ( buf ) );
+		fetch_raw_setting ( NULL, &pxe_boot_servers_setting,
+				    buf, sizeof ( buf ) );
 		pxebs_list ( dhcp, buf, sizeof ( buf ), ip );
 	}
 	if ( ! dhcp->pxe_attempt->s_addr ) {
diff --git a/src/net/udp/dhcpv6.c b/src/net/udp/dhcpv6.c
index 42d11194..7bed83d9 100644
--- a/src/net/udp/dhcpv6.c
+++ b/src/net/udp/dhcpv6.c
@@ -256,7 +256,7 @@ static int dhcpv6_iaaddr ( struct dhcpv6_option_list *options, uint32_t iaid,
  */
 
 /** DHCPv6 settings scope */
-static struct settings_scope dhcpv6_settings_scope;
+static const struct settings_scope dhcpv6_settings_scope;
 
 /** A DHCPv6 settings block */
 struct dhcpv6_settings {
@@ -276,7 +276,7 @@ struct dhcpv6_settings {
  * @ret applies		Setting applies within this settings block
  */
 static int dhcpv6_applies ( struct settings *settings __unused,
-			    struct setting *setting ) {
+			    const struct setting *setting ) {
 
 	return ( setting->scope == &dhcpv6_settings_scope );
 }
@@ -543,7 +543,7 @@ static size_t dhcpv6_user_class ( void *data, size_t len ) {
 	int actual_len;
 
 	/* Fetch user-class setting, if defined */
-	actual_len = fetch_setting ( NULL, &user_class_setting, data, len );
+	actual_len = fetch_raw_setting ( NULL, &user_class_setting, data, len );
 	if ( actual_len >= 0 )
 		return actual_len;
 
diff --git a/src/net/udp/dns.c b/src/net/udp/dns.c
index 45f0f07c..447da8af 100644
--- a/src/net/udp/dns.c
+++ b/src/net/udp/dns.c
@@ -594,7 +594,7 @@ struct resolver dns_resolver __resolver ( RESOLV_NORMAL ) = {
  */
 
 /** DNS server setting */
-struct setting dns_setting __setting ( SETTING_IPv4_EXTRA ) = {
+const struct setting dns_setting __setting ( SETTING_IPv4_EXTRA ) = {
 	.name = "dns",
 	.description = "DNS server",
 	.tag = DHCP_DNS_SERVERS,
@@ -622,11 +622,7 @@ static int apply_dns_settings ( void ) {
 
 	/* Get local domain DHCP option */
 	free ( localdomain );
-	if ( ( len = fetch_string_setting_copy ( NULL, &domain_setting,
-						 &localdomain ) ) < 0 ) {
-		DBG ( "DNS could not fetch local domain: %s\n",
-		      strerror ( len ) );
-	}
+	fetch_string_setting_copy ( NULL, &domain_setting, &localdomain );
 	if ( localdomain )
 		DBG ( "DNS local domain %s\n", localdomain );
 
diff --git a/src/net/udp/syslog.c b/src/net/udp/syslog.c
index 4210083d..6554ab9b 100644
--- a/src/net/udp/syslog.c
+++ b/src/net/udp/syslog.c
@@ -188,7 +188,7 @@ struct console_driver syslog_console __console_driver = {
  */
 
 /** Syslog server setting */
-struct setting syslog_setting __setting ( SETTING_MISC ) = {
+const struct setting syslog_setting __setting ( SETTING_MISC ) = {
 	.name = "syslog",
 	.description = "Syslog server",
 	.tag = DHCP_LOG_SERVERS,
@@ -209,17 +209,9 @@ static int apply_syslog_settings ( void ) {
 
 	/* Fetch hostname and domain name */
 	free ( syslog_hostname );
-	if ( ( len = fetch_string_setting_copy ( NULL, &hostname_setting,
-						 &syslog_hostname ) ) < 0 ) {
-		rc = len;
-		DBG ( "SYSLOG could not fetch hostname: %s\n", strerror ( rc ));
-	}
+	fetch_string_setting_copy ( NULL, &hostname_setting, &syslog_hostname );
 	free ( syslog_domain );
-	if ( ( len = fetch_string_setting_copy ( NULL, &domain_setting,
-						 &syslog_domain ) ) < 0 ) {
-		rc = len;
-		DBG ( "SYSLOG could not fetch domain: %s\n", strerror ( rc ) );
-	}
+	fetch_string_setting_copy ( NULL, &domain_setting, &syslog_domain );
 
 	/* Fetch log server */
 	syslog_console.disabled = CONSOLE_DISABLED;
diff --git a/src/net/validator.c b/src/net/validator.c
index d61cb92f..56eebe3d 100644
--- a/src/net/validator.c
+++ b/src/net/validator.c
@@ -121,7 +121,7 @@ static struct interface_descriptor validator_job_desc =
  */
 
 /** Cross-signed certificate source setting */
-struct setting crosscert_setting __setting ( SETTING_CRYPTO ) = {
+const struct setting crosscert_setting __setting ( SETTING_CRYPTO ) = {
 	.name = "crosscert",
 	.description = "Cross-signed certificate source",
 	.tag = DHCP_EB_CROSS_CERT,
@@ -232,14 +232,7 @@ static int validator_start_download ( struct validator *validator,
 	int rc;
 
 	/* Determine cross-signed certificate source */
-	len = fetch_string_setting_copy ( NULL, &crosscert_setting,
-					  &crosscert_copy );
-	if ( len < 0 ) {
-		rc = len;
-		DBGC ( validator, "VALIDATOR %p could not fetch crosscert "
-		       "setting: %s\n", validator, strerror ( rc ) );
-		goto err_fetch_crosscert;
-	}
+	fetch_string_setting_copy ( NULL, &crosscert_setting, &crosscert_copy );
 	crosscert = ( crosscert_copy ? crosscert_copy : crosscert_default );
 
 	/* Allocate URI string */
@@ -279,7 +272,6 @@ static int validator_start_download ( struct validator *validator,
 	free ( uri_string );
  err_alloc_uri_string:
 	free ( crosscert_copy );
- err_fetch_crosscert:
 	return rc;
 }
 
diff --git a/src/tests/settings_test.c b/src/tests/settings_test.c
index 1be2cc32..5da31b4c 100644
--- a/src/tests/settings_test.c
+++ b/src/tests/settings_test.c
@@ -38,26 +38,26 @@ FILE_LICENCE ( GPL2_OR_LATER );
 /**
  * Report a formatted-store test result
  *
- * @v settings		Settings block
- * @v setting		Setting
- * @v formatted		Formatted value
- * @v raw_array		Expected raw value
+ * @v _settings		Settings block
+ * @v _setting		Setting
+ * @v _formatted	Formatted value
+ * @v _raw_array	Expected raw value
  */
-#define storef_ok( settings, setting, formatted, raw_array ) do {	\
-	const uint8_t expected[] = raw_array;				\
+#define storef_ok( _settings, _setting, _formatted, _raw_array ) do {	\
+	const uint8_t expected[] = _raw_array;				\
 	uint8_t actual[ sizeof ( expected ) ];				\
 	int len;							\
 									\
-	ok ( storef_setting ( settings, setting, formatted ) == 0 );	\
-	len = fetch_setting ( settings, setting, actual,		\
+	ok ( storef_setting ( _settings, _setting, _formatted ) == 0 );	\
+	len = fetch_setting ( _settings, _setting, NULL, NULL, actual,	\
 			      sizeof ( actual ) );			\
 	if ( len >= 0 ) {						\
-		DBGC ( settings, "Stored %s \"%s\", got:\n",		\
-		       (setting)->type->name, formatted );		\
-		DBGC_HDA ( settings, 0, actual, len );			\
+		DBGC ( _settings, "Stored %s \"%s\", got:\n",		\
+		       (_setting)->type->name, _formatted );		\
+		DBGC_HDA ( _settings, 0, actual, len );			\
 	} else {							\
-		DBGC ( settings, "Stored %s \"%s\", got error %s\n",	\
-		       (setting)->type->name, formatted,		\
+		DBGC ( _settings, "Stored %s \"%s\", got error %s\n",	\
+		       (_setting)->type->name, _formatted,		\
 		       strerror ( len ) );				\
 	}								\
 	ok ( len == ( int ) sizeof ( actual ) );			\
@@ -67,52 +67,52 @@ FILE_LICENCE ( GPL2_OR_LATER );
 /**
  * Report a formatted-fetch test result
  *
- * @v settings		Settings block
- * @v setting		Setting
- * @v raw_array		Raw value
- * @v formatted		Expected formatted value
+ * @v _settings		Settings block
+ * @v _setting		Setting
+ * @v _raw_array	Raw value
+ * @v _formatted	Expected formatted value
  */
-#define fetchf_ok( settings, setting, raw_array, formatted ) do {	\
-	const uint8_t raw[] = raw_array;				\
-	char actual[ strlen ( formatted ) + 1 ];			\
+#define fetchf_ok( _settings, _setting, _raw_array, _formatted ) do {	\
+	const uint8_t raw[] = _raw_array;				\
+	char actual[ strlen ( _formatted ) + 1 ];			\
 	int len;							\
 									\
-	ok ( store_setting ( settings, setting, raw,			\
+	ok ( store_setting ( _settings, _setting, raw,			\
 			     sizeof ( raw ) ) == 0 );			\
-	len = fetchf_setting ( settings, setting, actual,		\
+	len = fetchf_setting ( _settings, _setting, NULL, NULL, actual,	\
 			       sizeof ( actual ) );			\
-	DBGC ( settings, "Fetched %s \"%s\" from:\n",			\
-	       (setting)->type->name, actual );				\
-	DBGC_HDA ( settings, 0, raw, sizeof ( raw ) );			\
+	DBGC ( _settings, "Fetched %s \"%s\" from:\n",			\
+	       (_setting)->type->name, actual );			\
+	DBGC_HDA ( _settings, 0, raw, sizeof ( raw ) );			\
 	ok ( len == ( int ) ( sizeof ( actual ) - 1 ) );		\
-	ok ( strcmp ( actual, formatted ) == 0 );			\
+	ok ( strcmp ( actual, _formatted ) == 0 );			\
 	} while ( 0 )
 
 /**
  * Report a numeric-store test result
  *
- * @v settings		Settings block
- * @v setting		Setting
- * @v numeric		Numeric value
- * @v raw_array		Expected raw value
+ * @v _settings		Settings block
+ * @v _setting		Setting
+ * @v _numeric		Numeric value
+ * @v _raw_array	Expected raw value
  */
-#define storen_ok( settings, setting, numeric, raw_array ) do {		\
-	const uint8_t expected[] = raw_array;				\
+#define storen_ok( _settings, _setting, _numeric, _raw_array ) do {	\
+	const uint8_t expected[] = _raw_array;				\
 	uint8_t actual[ sizeof ( expected ) ];				\
 	int len;							\
 									\
-	ok ( storen_setting ( settings, setting, numeric ) == 0 );	\
-	len = fetch_setting ( settings, setting, actual,		\
+	ok ( storen_setting ( _settings, _setting, _numeric ) == 0 );	\
+	len = fetch_setting ( _settings, _setting, NULL, NULL, actual,	\
 			      sizeof ( actual ) );			\
 	if ( len >= 0 ) {						\
-		DBGC ( settings, "Stored %s %#lx, got:\n",		\
-		       (setting)->type->name,				\
-		       ( unsigned long ) numeric );			\
-		DBGC_HDA ( settings, 0, actual, len );			\
+		DBGC ( _settings, "Stored %s %#lx, got:\n",		\
+		       (_setting)->type->name,				\
+		       ( unsigned long ) _numeric );			\
+		DBGC_HDA ( _settings, 0, actual, len );			\
 	} else {							\
-		DBGC ( settings, "Stored %s %#lx, got error %s\n",	\
-		       (setting)->type->name,				\
-		       ( unsigned long ) numeric, strerror ( len ) );	\
+		DBGC ( _settings, "Stored %s %#lx, got error %s\n",	\
+		       (_setting)->type->name,				\
+		       ( unsigned long ) _numeric, strerror ( len ) );	\
 	}								\
 	ok ( len == ( int ) sizeof ( actual ) );			\
 	ok ( memcmp ( actual, expected, sizeof ( actual ) ) == 0 );	\
@@ -121,22 +121,23 @@ FILE_LICENCE ( GPL2_OR_LATER );
 /**
  * Report a numeric-fetch test result
  *
- * @v settings		Settings block
- * @v setting		Setting
- * @v raw_array		Raw array
- * @v numeric		Expected numeric value
+ * @v _settings		Settings block
+ * @v _setting		Setting
+ * @v _raw_array	Raw array
+ * @v _numeric		Expected numeric value
  */
-#define fetchn_ok( settings, setting, raw_array, numeric ) do {		\
-	const uint8_t raw[] = raw_array;				\
+#define fetchn_ok( _settings, _setting, _raw_array, _numeric ) do {	\
+	const uint8_t raw[] = _raw_array;				\
 	unsigned long actual;						\
 									\
-	ok ( store_setting ( settings, setting, raw,			\
+	ok ( store_setting ( _settings, _setting, raw,			\
 			     sizeof ( raw ) ) == 0 );			\
-	ok ( fetchn_setting ( settings, setting, &actual ) == 0 );	\
-	DBGC ( settings, "Fetched %s %#lx from:\n",			\
-	       (setting)->type->name, actual );				\
-	DBGC_HDA ( settings, 0, raw, sizeof ( raw ) );			\
-	ok ( actual == ( unsigned long ) numeric );			\
+	ok ( fetchn_setting ( _settings, _setting, NULL, NULL,		\
+			      &actual ) == 0 );				\
+	DBGC ( _settings, "Fetched %s %#lx from:\n",			\
+	       (_setting)->type->name, actual );			\
+	DBGC_HDA ( _settings, 0, raw, sizeof ( raw ) );			\
+	ok ( actual == ( unsigned long ) _numeric );			\
 	} while ( 0 )
 
 /** Test generic settings block */
diff --git a/src/usr/autoboot.c b/src/usr/autoboot.c
index 6d6419d6..a29f8c17 100644
--- a/src/usr/autoboot.c
+++ b/src/usr/autoboot.c
@@ -59,7 +59,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #define CYAN	"\033[36m"
 
 /** The "scriptlet" setting */
-struct setting scriptlet_setting __setting ( SETTING_MISC ) = {
+const struct setting scriptlet_setting __setting ( SETTING_MISC ) = {
 	.name = "scriptlet",
 	.description = "Boot scriptlet",
 	.tag = DHCP_EB_SCRIPTLET,
@@ -119,7 +119,7 @@ static struct uri * parse_next_server_and_filename ( struct in_addr next_server,
 }
 
 /** The "keep-san" setting */
-struct setting keep_san_setting __setting ( SETTING_SANBOOT_EXTRA ) = {
+const struct setting keep_san_setting __setting ( SETTING_SANBOOT_EXTRA ) = {
 	.name = "keep-san",
 	.description = "Preserve SAN connection",
 	.tag = DHCP_EB_KEEP_SAN,
@@ -127,7 +127,7 @@ struct setting keep_san_setting __setting ( SETTING_SANBOOT_EXTRA ) = {
 };
 
 /** The "skip-san-boot" setting */
-struct setting skip_san_boot_setting __setting ( SETTING_SANBOOT_EXTRA ) = {
+const struct setting skip_san_boot_setting __setting ( SETTING_SANBOOT_EXTRA )={
 	.name = "skip-san-boot",
 	.description = "Do not boot from SAN device",
 	.tag = DHCP_EB_SKIP_SAN_BOOT,
@@ -256,16 +256,15 @@ struct uri * fetch_next_server_and_filename ( struct settings *settings ) {
 	struct uri *uri = NULL;
 	char *filename;
 
-	/* Determine settings block containing the filename, if any */
-	settings = fetch_setting_origin ( settings, &filename_setting );
-
-	/* If we have a filename, fetch it along with next-server */
-	if ( settings ) {
+	/* If we have a filename, fetch it along with the next-server
+	 * setting from the same settings block.
+	 */
+	if ( fetch_setting ( settings, &filename_setting, &settings,
+			     NULL, NULL, 0 ) >= 0 ) {
+		fetch_string_setting_copy ( settings, &filename_setting,
+					    &raw_filename );
 		fetch_ipv4_setting ( settings, &next_server_setting,
 				     &next_server );
-		if ( fetch_string_setting_copy ( settings, &filename_setting,
-						 &raw_filename ) < 0 )
-			goto err_fetch;
 	}
 
 	/* Expand filename setting */
@@ -286,7 +285,6 @@ struct uri * fetch_next_server_and_filename ( struct settings *settings ) {
 	free ( filename );
  err_expand:
 	free ( raw_filename );
- err_fetch:
 	return uri;
 }
 
@@ -297,25 +295,30 @@ struct uri * fetch_next_server_and_filename ( struct settings *settings ) {
  * @ret uri		URI, or NULL on failure
  */
 static struct uri * fetch_root_path ( struct settings *settings ) {
-	char buf[256];
+	struct uri *uri = NULL;
+	char *raw_root_path;
 	char *root_path;
-	struct uri *uri;
 
 	/* Fetch root-path setting */
-	fetch_string_setting ( settings, &root_path_setting,
-			       buf, sizeof ( buf ) );
-	if ( buf[0] )
-		printf ( "Root path: %s\n", buf );
+	fetch_string_setting_copy ( settings, &root_path_setting,
+				    &raw_root_path );
 
 	/* Expand filename setting */
-	root_path = expand_settings ( buf );
+	root_path = expand_settings ( raw_root_path ? raw_root_path : "" );
 	if ( ! root_path )
-		return NULL;
+		goto err_expand;
 
 	/* Parse root path */
+	if ( root_path[0] )
+		printf ( "Root path: %s\n", root_path );
 	uri = parse_uri ( root_path );
+	if ( ! uri )
+		goto err_parse;
 
+ err_parse:
 	free ( root_path );
+ err_expand:
+	free ( raw_root_path );
 	return uri;
 }
 
@@ -331,7 +334,7 @@ static int have_pxe_menu ( void ) {
 		= { .tag = DHCP_PXE_DISCOVERY_CONTROL };
 	struct setting pxe_boot_menu_setting
 		= { .tag = DHCP_PXE_BOOT_MENU };
-	char buf[256];
+	char buf[ 10 /* "PXEClient" + NUL */ ];
 	unsigned int pxe_discovery_control;
 
 	fetch_string_setting ( NULL, &vendor_class_id_setting,
diff --git a/src/usr/nslookup.c b/src/usr/nslookup.c
index b691962e..66818d11 100644
--- a/src/usr/nslookup.c
+++ b/src/usr/nslookup.c
@@ -71,7 +71,7 @@ static void nslookup_close ( struct nslookup *nslookup, int rc ) {
 static void nslookup_resolv_done ( struct nslookup *nslookup,
 				   struct sockaddr *sa ) {
 	struct sockaddr_in *sin;
-	struct setting_type *default_type;
+	const struct setting_type *default_type;
 	struct settings *settings;
 	struct setting setting;
 	void *data;
diff --git a/src/usr/pxemenu.c b/src/usr/pxemenu.c
index d50ee6ba..c5cffd3d 100644
--- a/src/usr/pxemenu.c
+++ b/src/usr/pxemenu.c
@@ -101,9 +101,9 @@ static int pxe_menu_parse ( struct pxe_menu **menu ) {
 
 	/* Fetch raw menu */
 	memset ( raw_menu, 0, sizeof ( raw_menu ) );
-	if ( ( raw_menu_len = fetch_setting ( NULL, &pxe_boot_menu_setting,
-					      raw_menu,
-					      sizeof ( raw_menu ) ) ) < 0 ) {
+	if ( ( raw_menu_len = fetch_raw_setting ( NULL, &pxe_boot_menu_setting,
+						  raw_menu,
+						  sizeof ( raw_menu ) ) ) < 0 ){
 		rc = raw_menu_len;
 		DBG ( "Could not retrieve raw PXE boot menu: %s\n",
 		      strerror ( rc ) );
@@ -116,8 +116,9 @@ static int pxe_menu_parse ( struct pxe_menu **menu ) {
 	raw_menu_end = ( raw_menu + raw_menu_len );
 
 	/* Fetch raw prompt length */
-	raw_prompt_len = fetch_setting_len ( NULL,
-					     &pxe_boot_menu_prompt_setting );
+	raw_prompt_len =
+		fetch_raw_setting ( NULL, &pxe_boot_menu_prompt_setting,
+				    NULL, 0 );
 	if ( raw_prompt_len < 0 )
 		raw_prompt_len = 0;
 
@@ -168,8 +169,8 @@ static int pxe_menu_parse ( struct pxe_menu **menu ) {
 	if ( raw_prompt_len ) {
 		raw_menu_prompt = ( ( ( void * ) raw_menu_item ) +
 				    1 /* NUL */ );
-		fetch_setting ( NULL, &pxe_boot_menu_prompt_setting,
-				raw_menu_prompt, raw_prompt_len );
+		fetch_raw_setting ( NULL, &pxe_boot_menu_prompt_setting,
+				    raw_menu_prompt, raw_prompt_len );
 		(*menu)->timeout =
 			( ( raw_menu_prompt->timeout == 0xff ) ?
 			  -1 : raw_menu_prompt->timeout );