[interface] Convert all data-xfer interfaces to generic interfaces

Remove data-xfer as an interface type, and replace data-xfer
interfaces with generic interfaces supporting the data-xfer methods.

Filter interfaces (as used by the TLS layer) are handled using the
generic pass-through interface capability.  A side-effect of this is
that deliver_raw() no longer exists as a data-xfer method.  (In
practice this doesn't lose any efficiency, since there are no
instances within the current codebase where xfer_deliver_raw() is used
to pass data to an interface supporting the deliver_raw() method.)

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

12 files changed, 408 insertions, 636 deletions

diff --git a/src/net/infiniband/ib_cmrc.c b/src/net/infiniband/ib_cmrc.c
index b7b9cd819..f596c36dc 100644
--- a/src/net/infiniband/ib_cmrc.c
+++ b/src/net/infiniband/ib_cmrc.c
@@ -70,7 +70,7 @@ struct ib_cmrc_connection {
 	/** Reference count */
 	struct refcnt refcnt;
 	/** Data transfer interface */
-	struct xfer_interface xfer;
+	struct interface xfer;
 	/** Infiniband device */
 	struct ib_device *ibdev;
 	/** Completion queue */
@@ -135,8 +135,7 @@ static void ib_cmrc_shutdown ( struct process *process ) {
 static void ib_cmrc_close ( struct ib_cmrc_connection *cmrc, int rc ) {
 
 	/* Close data transfer interface */
-	xfer_nullify ( &cmrc->xfer );
-	xfer_close ( &cmrc->xfer, rc );
+	intf_shutdown ( &cmrc->xfer, rc );
 
 	/* Schedule shutdown process */
 	process_add ( &cmrc->shutdown );
@@ -263,16 +262,14 @@ static struct ib_completion_queue_operations ib_cmrc_completion_ops = {
 /**
  * Send data via CMRC
  *
- * @v xfer		Data transfer interface
+ * @v cmrc		CMRC connection
  * @v iobuf		Datagram I/O buffer
  * @v meta		Data transfer metadata
  * @ret rc		Return status code
  */
-static int ib_cmrc_xfer_deliver_iob ( struct xfer_interface *xfer,
-				      struct io_buffer *iobuf,
-				      struct xfer_metadata *meta __unused ) {
-	struct ib_cmrc_connection *cmrc =
-		container_of ( xfer, struct ib_cmrc_connection, xfer );
+static int ib_cmrc_xfer_deliver ( struct ib_cmrc_connection *cmrc,
+				  struct io_buffer *iobuf,
+				  struct xfer_metadata *meta __unused ) {
 	int rc;
 
 	/* If no connection has yet been attempted, send this datagram
@@ -326,12 +323,10 @@ static int ib_cmrc_xfer_deliver_iob ( struct xfer_interface *xfer,
 /**
  * Check CMRC flow control window
  *
- * @v xfer		Data transfer interface
+ * @v cmrc		CMRC connection
  * @ret len		Length of window
  */
-static size_t ib_cmrc_xfer_window ( struct xfer_interface *xfer ) {
-	struct ib_cmrc_connection *cmrc =
-		container_of ( xfer, struct ib_cmrc_connection, xfer );
+static size_t ib_cmrc_xfer_window ( struct ib_cmrc_connection *cmrc ) {
 
 	/* We indicate a window only when we are successfully
 	 * connected.
@@ -339,30 +334,19 @@ static size_t ib_cmrc_xfer_window ( struct xfer_interface *xfer ) {
 	return ( cmrc->connected ? IB_MAX_PAYLOAD_SIZE : 0 );
 }
 
-/**
- * Close CMRC data-transfer interface
- *
- * @v xfer		Data transfer interface
- * @v rc		Reason for close
- */
-static void ib_cmrc_xfer_close ( struct xfer_interface *xfer, int rc ) {
-	struct ib_cmrc_connection *cmrc =
-		container_of ( xfer, struct ib_cmrc_connection, xfer );
-
-	DBGC ( cmrc, "CMRC %p closed: %s\n", cmrc, strerror ( rc ) );
-	ib_cmrc_close ( cmrc, rc );
-}
-
 /** CMRC data transfer interface operations */
-static struct xfer_interface_operations ib_cmrc_xfer_operations = {
-	.close		= ib_cmrc_xfer_close,
-	.vredirect	= ignore_xfer_vredirect,
-	.window		= ib_cmrc_xfer_window,
-	.alloc_iob	= default_xfer_alloc_iob,
-	.deliver_iob	= ib_cmrc_xfer_deliver_iob,
-	.deliver_raw	= xfer_deliver_as_iob,
+static struct interface_operation ib_cmrc_xfer_operations[] = {
+	INTF_OP ( xfer_deliver, struct ib_cmrc_connection *,
+		  ib_cmrc_xfer_deliver ),
+	INTF_OP ( xfer_window, struct ib_cmrc_connection *,
+		  ib_cmrc_xfer_window ),
+	INTF_OP ( intf_close, struct ib_cmrc_connection *, ib_cmrc_close ),
 };
 
+/** CMRC data transfer interface descriptor */
+static struct interface_descriptor ib_cmrc_xfer_desc =
+	INTF_DESC ( struct ib_cmrc_connection, xfer, ib_cmrc_xfer_operations );
+
 /**
  * Open CMRC connection
  *
@@ -372,7 +356,7 @@ static struct xfer_interface_operations ib_cmrc_xfer_operations = {
  * @v service_id	Service ID
  * @ret rc		Returns status code
  */
-int ib_cmrc_open ( struct xfer_interface *xfer, struct ib_device *ibdev,
+int ib_cmrc_open ( struct interface *xfer, struct ib_device *ibdev,
 		   struct ib_gid *dgid, struct ib_gid_half *service_id ) {
 	struct ib_cmrc_connection *cmrc;
 	int rc;
@@ -384,7 +368,7 @@ int ib_cmrc_open ( struct xfer_interface *xfer, struct ib_device *ibdev,
 		goto err_alloc;
 	}
 	ref_init ( &cmrc->refcnt, NULL );
-	xfer_init ( &cmrc->xfer, &ib_cmrc_xfer_operations, &cmrc->refcnt );
+	intf_init ( &cmrc->xfer, &ib_cmrc_xfer_desc, &cmrc->refcnt );
 	cmrc->ibdev = ibdev;
 	memcpy ( &cmrc->dgid, dgid, sizeof ( cmrc->dgid ) );
 	memcpy ( &cmrc->service_id, service_id, sizeof ( cmrc->service_id ) );
@@ -422,7 +406,7 @@ int ib_cmrc_open ( struct xfer_interface *xfer, struct ib_device *ibdev,
 	/* Attach to parent interface, transfer reference (implicitly)
 	 * to our shutdown process, and return.
 	 */
-	xfer_plug_plug ( &cmrc->xfer, xfer );
+	intf_plug_plug ( &cmrc->xfer, xfer );
 	return 0;
 
 	ib_destroy_qp ( ibdev, cmrc->qp );
diff --git a/src/net/tcp.c b/src/net/tcp.c
index b5b9ff608..d64153f3e 100644
--- a/src/net/tcp.c
+++ b/src/net/tcp.c
@@ -31,7 +31,7 @@ struct tcp_connection {
 	struct list_head list;
 
 	/** Data transfer interface */
-	struct xfer_interface xfer;
+	struct interface xfer;
 	/** Data transfer interface closed flag */
 	int xfer_closed;
 
@@ -92,7 +92,7 @@ struct tcp_connection {
 static LIST_HEAD ( tcp_conns );
 
 /* Forward declarations */
-static struct xfer_interface_operations tcp_xfer_operations;
+static struct interface_descriptor tcp_xfer_desc;
 static void tcp_expired ( struct retry_timer *timer, int over );
 static int tcp_rx_ack ( struct tcp_connection *tcp, uint32_t ack,
 			uint32_t win );
@@ -211,7 +211,7 @@ static int tcp_bind ( struct tcp_connection *tcp, unsigned int port ) {
  * @v local		Local socket address, or NULL
  * @ret rc		Return status code
  */
-static int tcp_open ( struct xfer_interface *xfer, struct sockaddr *peer,
+static int tcp_open ( struct interface *xfer, struct sockaddr *peer,
 		      struct sockaddr *local ) {
 	struct sockaddr_tcpip *st_peer = ( struct sockaddr_tcpip * ) peer;
 	struct sockaddr_tcpip *st_local = ( struct sockaddr_tcpip * ) local;
@@ -225,7 +225,7 @@ static int tcp_open ( struct xfer_interface *xfer, struct sockaddr *peer,
 		return -ENOMEM;
 	DBGC ( tcp, "TCP %p allocated\n", tcp );
 	ref_init ( &tcp->refcnt, NULL );
-	xfer_init ( &tcp->xfer, &tcp_xfer_operations, &tcp->refcnt );
+	intf_init ( &tcp->xfer, &tcp_xfer_desc, &tcp->refcnt );
 	timer_init ( &tcp->timer, tcp_expired );
 	tcp->prev_tcp_state = TCP_CLOSED;
 	tcp->tcp_state = TCP_STATE_SENT ( TCP_SYN );
@@ -245,7 +245,7 @@ static int tcp_open ( struct xfer_interface *xfer, struct sockaddr *peer,
 	/* Attach parent interface, transfer reference to connection
 	 * list and return
 	 */
-	xfer_plug_plug ( &tcp->xfer, xfer );
+	intf_plug_plug ( &tcp->xfer, xfer );
 	list_add ( &tcp->list, &tcp_conns );
 	return 0;
 
@@ -268,8 +268,7 @@ static void tcp_close ( struct tcp_connection *tcp, int rc ) {
 	struct io_buffer *tmp;
 
 	/* Close data transfer interface */
-	xfer_nullify ( &tcp->xfer );
-	xfer_close ( &tcp->xfer, rc );
+	intf_shutdown ( &tcp->xfer, rc );
 	tcp->xfer_closed = 1;
 
 	/* If we are in CLOSED, or have otherwise not yet received a
@@ -1044,12 +1043,10 @@ struct tcpip_protocol tcp_protocol __tcpip_protocol = {
 /**
  * Close interface
  *
- * @v xfer		Data transfer interface
+ * @v tcp		TCP connection
  * @v rc		Reason for close
  */
-static void tcp_xfer_close ( struct xfer_interface *xfer, int rc ) {
-	struct tcp_connection *tcp =
-		container_of ( xfer, struct tcp_connection, xfer );
+static void tcp_xfer_close ( struct tcp_connection *tcp, int rc ) {
 
 	/* Close data transfer interface */
 	tcp_close ( tcp, rc );
@@ -1061,12 +1058,10 @@ static void tcp_xfer_close ( struct xfer_interface *xfer, int rc ) {
 /**
  * Check flow control window
  *
- * @v xfer		Data transfer interface
+ * @v tcp		TCP connection
  * @ret len		Length of window
  */
-static size_t tcp_xfer_window ( struct xfer_interface *xfer ) {
-	struct tcp_connection *tcp =
-		container_of ( xfer, struct tcp_connection, xfer );
+static size_t tcp_xfer_window ( struct tcp_connection *tcp ) {
 
 	/* Not ready if data queue is non-empty.  This imposes a limit
 	 * of only one unACKed packet in the TX queue at any time; we
@@ -1082,16 +1077,14 @@ static size_t tcp_xfer_window ( struct xfer_interface *xfer ) {
 /**
  * Deliver datagram as I/O buffer
  *
- * @v xfer		Data transfer interface
+ * @v tcp		TCP connection
  * @v iobuf		Datagram I/O buffer
  * @v meta		Data transfer metadata
  * @ret rc		Return status code
  */
-static int tcp_xfer_deliver_iob ( struct xfer_interface *xfer,
-				  struct io_buffer *iobuf,
-				  struct xfer_metadata *meta __unused ) {
-	struct tcp_connection *tcp =
-		container_of ( xfer, struct tcp_connection, xfer );
+static int tcp_xfer_deliver ( struct tcp_connection *tcp,
+			      struct io_buffer *iobuf,
+			      struct xfer_metadata *meta __unused ) {
 
 	/* Enqueue packet */
 	list_add_tail ( &iobuf->list, &tcp->queue );
@@ -1103,15 +1096,16 @@ static int tcp_xfer_deliver_iob ( struct xfer_interface *xfer,
 }
 
 /** TCP data transfer interface operations */
-static struct xfer_interface_operations tcp_xfer_operations = {
-	.close		= tcp_xfer_close,
-	.vredirect	= ignore_xfer_vredirect,
-	.window		= tcp_xfer_window,
-	.alloc_iob	= default_xfer_alloc_iob,
-	.deliver_iob	= tcp_xfer_deliver_iob,
-	.deliver_raw	= xfer_deliver_as_iob,
+static struct interface_operation tcp_xfer_operations[] = {
+	INTF_OP ( xfer_deliver, struct tcp_connection *, tcp_xfer_deliver ),
+	INTF_OP ( xfer_window, struct tcp_connection *, tcp_xfer_window ),
+	INTF_OP ( intf_close, struct tcp_connection *, tcp_xfer_close ),
 };
 
+/** TCP data transfer interface descriptor */
+static struct interface_descriptor tcp_xfer_desc =
+	INTF_DESC ( struct tcp_connection, xfer, tcp_xfer_operations );
+
 /***************************************************************************
  *
  * Openers
@@ -1136,7 +1130,7 @@ int tcp_sock_stream = TCP_SOCK_STREAM;
  * @v uri		URI
  * @ret rc		Return status code
  */
-static int tcp_open_uri ( struct xfer_interface *xfer, struct uri *uri ) {
+static int tcp_open_uri ( struct interface *xfer, struct uri *uri ) {
 	struct sockaddr_tcpip peer;
 
 	/* Sanity check */
diff --git a/src/net/tcp/ftp.c b/src/net/tcp/ftp.c
index 58794c8b2..957f05cc8 100644
--- a/src/net/tcp/ftp.c
+++ b/src/net/tcp/ftp.c
@@ -8,6 +8,7 @@
 #include <ipxe/socket.h>
 #include <ipxe/tcpip.h>
 #include <ipxe/in.h>
+#include <ipxe/iobuf.h>
 #include <ipxe/xfer.h>
 #include <ipxe/open.h>
 #include <ipxe/uri.h>
@@ -48,14 +49,14 @@ struct ftp_request {
 	/** Reference counter */
 	struct refcnt refcnt;
 	/** Data transfer interface */
-	struct xfer_interface xfer;
+	struct interface xfer;
 
 	/** URI being fetched */
 	struct uri *uri;
 	/** FTP control channel interface */
-	struct xfer_interface control;
+	struct interface control;
 	/** FTP data channel interface */
-	struct xfer_interface data;
+	struct interface data;
 
 	/** Current state */
 	enum ftp_state state;
@@ -95,12 +96,9 @@ static void ftp_done ( struct ftp_request *ftp, int rc ) {
 	DBGC ( ftp, "FTP %p completed (%s)\n", ftp, strerror ( rc ) );
 
 	/* Close all data transfer interfaces */
-	xfer_nullify ( &ftp->xfer );
-	xfer_close ( &ftp->xfer, rc );
-	xfer_nullify ( &ftp->control );
-	xfer_close ( &ftp->control, rc );
-	xfer_nullify ( &ftp->data );
-	xfer_close ( &ftp->data, rc );
+	intf_shutdown ( &ftp->data, rc );
+	intf_shutdown ( &ftp->control, rc );
+	intf_shutdown ( &ftp->xfer, rc );
 }
 
 /*****************************************************************************
@@ -167,26 +165,6 @@ static struct ftp_control_string ftp_strings[] = {
 };
 
 /**
- * Handle control channel being closed
- *
- * @v control		FTP control channel interface
- * @v rc		Reason for close
- *
- * When the control channel is closed, the data channel must also be
- * closed, if it is currently open.
- */
-static void ftp_control_close ( struct xfer_interface *control, int rc ) {
-	struct ftp_request *ftp =
-		container_of ( control, struct ftp_request, control );
-
-	DBGC ( ftp, "FTP %p control connection closed: %s\n",
-	       ftp, strerror ( rc ) );
-
-	/* Complete FTP operation */
-	ftp_done ( ftp, rc );
-}
-
-/**
  * Parse FTP byte sequence value
  *
  * @v text		Text string
@@ -298,23 +276,25 @@ static void ftp_reply ( struct ftp_request *ftp ) {
 /**
  * Handle new data arriving on FTP control channel
  *
- * @v control		FTP control channel interface
- * @v data		New data
- * @v len		Length of new data
+ * @v ftp		FTP request
+ * @v iob		I/O buffer
+ * @v meta		Data transfer metadata
+ * @ret rc		Return status code
  *
  * Data is collected until a complete line is received, at which point
  * its information is passed to ftp_reply().
  */
-static int ftp_control_deliver_raw ( struct xfer_interface *control,
-				     const void *data, size_t len ) {
-	struct ftp_request *ftp =
-		container_of ( control, struct ftp_request, control );
+static int ftp_control_deliver ( struct ftp_request *ftp,
+				 struct io_buffer *iobuf,
+				 struct xfer_metadata *meta __unused ) {
+	char *data = iobuf->data;
+	size_t len = iob_len ( iobuf );
 	char *recvbuf = ftp->recvbuf;
 	size_t recvsize = ftp->recvsize;
 	char c;
 	
 	while ( len-- ) {
-		c = * ( ( char * ) data++ );
+		c = *(data++);
 		switch ( c ) {
 		case '\r' :
 		case '\n' :
@@ -351,19 +331,22 @@ static int ftp_control_deliver_raw ( struct xfer_interface *control,
 	ftp->recvbuf = recvbuf;
 	ftp->recvsize = recvsize;
 
+	/* Free I/O buffer */
+	free_iob ( iobuf );
+
 	return 0;
 }
 
-/** FTP control channel operations */
-static struct xfer_interface_operations ftp_control_operations = {
-	.close		= ftp_control_close,
-	.vredirect	= xfer_vreopen,
-	.window		= unlimited_xfer_window,
-	.alloc_iob	= default_xfer_alloc_iob,
-	.deliver_iob	= xfer_deliver_as_raw,
-	.deliver_raw	= ftp_control_deliver_raw,
+/** FTP control channel interface operations */
+static struct interface_operation ftp_control_operations[] = {
+	INTF_OP ( xfer_deliver, struct ftp_request *, ftp_control_deliver ),
+	INTF_OP ( intf_close, struct ftp_request *, ftp_done ),
 };
 
+/** FTP control channel interface descriptor */
+static struct interface_descriptor ftp_control_desc =
+	INTF_DESC ( struct ftp_request, control, ftp_control_operations );
+
 /*****************************************************************************
  *
  * FTP data channel
@@ -373,7 +356,7 @@ static struct xfer_interface_operations ftp_control_operations = {
 /**
  * Handle FTP data channel being closed
  *
- * @v data		FTP data channel interface
+ * @v ftp		FTP request
  * @v rc		Reason for closure
  *
  * When the data channel is closed, the control channel should be left
@@ -382,9 +365,7 @@ static struct xfer_interface_operations ftp_control_operations = {
  *
  * If the data channel is closed due to an error, we abort the request.
  */
-static void ftp_data_closed ( struct xfer_interface *data, int rc ) {
-	struct ftp_request *ftp =
-		container_of ( data, struct ftp_request, data );
+static void ftp_data_closed ( struct ftp_request *ftp, int rc ) {
 
 	DBGC ( ftp, "FTP %p data connection closed: %s\n",
 	       ftp, strerror ( rc ) );
@@ -400,16 +381,14 @@ static void ftp_data_closed ( struct xfer_interface *data, int rc ) {
 /**
  * Handle data delivery via FTP data channel
  *
- * @v xfer		FTP data channel interface
+ * @v ftp		FTP request
  * @v iobuf		I/O buffer
  * @v meta		Data transfer metadata
  * @ret rc		Return status code
  */
-static int ftp_data_deliver_iob ( struct xfer_interface *data,
-				  struct io_buffer *iobuf,
-				  struct xfer_metadata *meta __unused ) {
-	struct ftp_request *ftp =
-		container_of ( data, struct ftp_request, data );
+static int ftp_data_deliver ( struct ftp_request *ftp,
+			      struct io_buffer *iobuf,
+			      struct xfer_metadata *meta __unused ) {
 	int rc;
 
 	if ( ( rc = xfer_deliver_iob ( &ftp->xfer, iobuf ) ) != 0 ) {
@@ -421,48 +400,31 @@ static int ftp_data_deliver_iob ( struct xfer_interface *data,
 	return 0;
 }
 
-/** FTP data channel operations */
-static struct xfer_interface_operations ftp_data_operations = {
-	.close		= ftp_data_closed,
-	.vredirect	= xfer_vreopen,
-	.window		= unlimited_xfer_window,
-	.alloc_iob	= default_xfer_alloc_iob,
-	.deliver_iob	= ftp_data_deliver_iob,
-	.deliver_raw	= xfer_deliver_as_iob,
+/** FTP data channel interface operations */
+static struct interface_operation ftp_data_operations[] = {
+	INTF_OP ( xfer_deliver, struct ftp_request *, ftp_data_deliver ),
+	INTF_OP ( intf_close, struct ftp_request *, ftp_data_closed ),
 };
 
+/** FTP data channel interface descriptor */
+static struct interface_descriptor ftp_data_desc =
+	INTF_DESC ( struct ftp_request, data, ftp_data_operations );
+
 /*****************************************************************************
  *
  * Data transfer interface
  *
  */
 
-/**
- * Close FTP data transfer interface
- *
- * @v xfer		FTP data transfer interface
- * @v rc		Reason for close
- */
-static void ftp_xfer_closed ( struct xfer_interface *xfer, int rc ) {
-	struct ftp_request *ftp =
-		container_of ( xfer, struct ftp_request, xfer );
-
-	DBGC ( ftp, "FTP %p data transfer interface closed: %s\n",
-	       ftp, strerror ( rc ) );
-	
-	ftp_done ( ftp, rc );
-}
-
 /** FTP data transfer interface operations */
-static struct xfer_interface_operations ftp_xfer_operations = {
-	.close		= ftp_xfer_closed,
-	.vredirect	= ignore_xfer_vredirect,
-	.window		= unlimited_xfer_window,
-	.alloc_iob	= default_xfer_alloc_iob,
-	.deliver_iob	= xfer_deliver_as_raw,
-	.deliver_raw	= ignore_xfer_deliver_raw,
+static struct interface_operation ftp_xfer_operations[] = {
+	INTF_OP ( intf_close, struct ftp_request *, ftp_done ),
 };
 
+/** FTP data transfer interface descriptor */
+static struct interface_descriptor ftp_xfer_desc =
+	INTF_DESC ( struct ftp_request, xfer, ftp_xfer_operations );
+
 /*****************************************************************************
  *
  * URI opener
@@ -476,7 +438,7 @@ static struct xfer_interface_operations ftp_xfer_operations = {
  * @v uri		Uniform Resource Identifier
  * @ret rc		Return status code
  */
-static int ftp_open ( struct xfer_interface *xfer, struct uri *uri ) {
+static int ftp_open ( struct interface *xfer, struct uri *uri ) {
 	struct ftp_request *ftp;
 	struct sockaddr_tcpip server;
 	int rc;
@@ -492,10 +454,10 @@ static int ftp_open ( struct xfer_interface *xfer, struct uri *uri ) {
 	if ( ! ftp )
 		return -ENOMEM;
 	ref_init ( &ftp->refcnt, ftp_free );
-	xfer_init ( &ftp->xfer, &ftp_xfer_operations, &ftp->refcnt );
+	intf_init ( &ftp->xfer, &ftp_xfer_desc, &ftp->refcnt );
+	intf_init ( &ftp->control, &ftp_control_desc, &ftp->refcnt );
+	intf_init ( &ftp->data, &ftp_data_desc, &ftp->refcnt );
 	ftp->uri = uri_get ( uri );
-	xfer_init ( &ftp->control, &ftp_control_operations, &ftp->refcnt );
-	xfer_init ( &ftp->data, &ftp_data_operations, &ftp->refcnt );
 	ftp->recvbuf = ftp->status_text;
 	ftp->recvsize = sizeof ( ftp->status_text ) - 1;
 
@@ -510,7 +472,7 @@ static int ftp_open ( struct xfer_interface *xfer, struct uri *uri ) {
 		goto err;
 
 	/* Attach to parent interface, mortalise self, and return */
-	xfer_plug_plug ( &ftp->xfer, xfer );
+	intf_plug_plug ( &ftp->xfer, xfer );
 	ref_put ( &ftp->refcnt );
 	return 0;
 
diff --git a/src/net/tcp/http.c b/src/net/tcp/http.c
index d6a9fad7e..13c500d50 100644
--- a/src/net/tcp/http.c
+++ b/src/net/tcp/http.c
@@ -64,12 +64,12 @@ struct http_request {
 	/** Reference count */
 	struct refcnt refcnt;
 	/** Data transfer interface */
-	struct xfer_interface xfer;
+	struct interface xfer;
 
 	/** URI being fetched */
 	struct uri *uri;
 	/** Transport layer interface */
-	struct xfer_interface socket;
+	struct interface socket;
 
 	/** TX process */
 	struct process process;
@@ -125,10 +125,8 @@ static void http_done ( struct http_request *http, int rc ) {
 	process_del ( &http->process );
 
 	/* Close all data transfer interfaces */
-	xfer_nullify ( &http->socket );
-	xfer_close ( &http->socket, rc );
-	xfer_nullify ( &http->xfer );
-	xfer_close ( &http->xfer, rc );
+	intf_shutdown ( &http->socket, rc );
+	intf_shutdown ( &http->xfer, rc );
 }
 
 /**
@@ -349,16 +347,14 @@ static int http_rx_data ( struct http_request *http,
 /**
  * Handle new data arriving via HTTP connection
  *
- * @v socket		Transport layer interface
+ * @v http		HTTP request
  * @v iobuf		I/O buffer
  * @v meta		Data transfer metadata
  * @ret rc		Return status code
  */
-static int http_socket_deliver_iob ( struct xfer_interface *socket,
-				     struct io_buffer *iobuf,
-				     struct xfer_metadata *meta __unused ) {
-	struct http_request *http =
-		container_of ( socket, struct http_request, socket );
+static int http_socket_deliver ( struct http_request *http,
+				 struct io_buffer *iobuf,
+				 struct xfer_metadata *meta __unused ) {
 	struct http_line_handler *lh;
 	char *line;
 	ssize_t len;
@@ -469,58 +465,25 @@ static void http_step ( struct process *process ) {
 	}
 }
 
-/**
- * HTTP connection closed by network stack
- *
- * @v socket		Transport layer interface
- * @v rc		Reason for close
- */
-static void http_socket_close ( struct xfer_interface *socket, int rc ) {
-	struct http_request *http =
-		container_of ( socket, struct http_request, socket );
-
-	DBGC ( http, "HTTP %p socket closed: %s\n",
-	       http, strerror ( rc ) );
-	
-	http_done ( http, rc );
-}
-
-/** HTTP socket operations */
-static struct xfer_interface_operations http_socket_operations = {
-	.close		= http_socket_close,
-	.vredirect	= xfer_vreopen,
-	.window		= unlimited_xfer_window,
-	.alloc_iob	= default_xfer_alloc_iob,
-	.deliver_iob	= http_socket_deliver_iob,
-	.deliver_raw	= xfer_deliver_as_iob,
+/** HTTP socket interface operations */
+static struct interface_operation http_socket_operations[] = {
+	INTF_OP ( xfer_deliver, struct http_request *, http_socket_deliver ),
+	INTF_OP ( intf_close, struct http_request *, http_done ),
 };
 
-/**
- * Close HTTP data transfer interface
- *
- * @v xfer		Data transfer interface
- * @v rc		Reason for close
- */
-static void http_xfer_close ( struct xfer_interface *xfer, int rc ) {
-	struct http_request *http =
-		container_of ( xfer, struct http_request, xfer );
-
-	DBGC ( http, "HTTP %p interface closed: %s\n",
-	       http, strerror ( rc ) );
-
-	http_done ( http, rc );
-}
+/** HTTP socket interface descriptor */
+static struct interface_descriptor http_socket_desc =
+	INTF_DESC ( struct http_request, socket, http_socket_operations );
 
 /** HTTP data transfer interface operations */
-static struct xfer_interface_operations http_xfer_operations = {
-	.close		= http_xfer_close,
-	.vredirect	= ignore_xfer_vredirect,
-	.window		= unlimited_xfer_window,
-	.alloc_iob	= default_xfer_alloc_iob,
-	.deliver_iob	= xfer_deliver_as_raw,
-	.deliver_raw	= ignore_xfer_deliver_raw,
+static struct interface_operation http_xfer_operations[] = {
+	INTF_OP ( intf_close, struct http_request *, http_done ),
 };
 
+/** HTTP data transfer interface descriptor */
+static struct interface_descriptor http_xfer_desc =
+	INTF_DESC ( struct http_request, xfer, http_xfer_operations );
+
 /**
  * Initiate an HTTP connection, with optional filter
  *
@@ -530,13 +493,13 @@ static struct xfer_interface_operations http_xfer_operations = {
  * @v filter		Filter to apply to socket, or NULL
  * @ret rc		Return status code
  */
-int http_open_filter ( struct xfer_interface *xfer, struct uri *uri,
+int http_open_filter ( struct interface *xfer, struct uri *uri,
 		       unsigned int default_port,
-		       int ( * filter ) ( struct xfer_interface *xfer,
-					  struct xfer_interface **next ) ) {
+		       int ( * filter ) ( struct interface *xfer,
+					  struct interface **next ) ) {
 	struct http_request *http;
 	struct sockaddr_tcpip server;
-	struct xfer_interface *socket;
+	struct interface *socket;
 	int rc;
 
 	/* Sanity checks */
@@ -548,9 +511,9 @@ int http_open_filter ( struct xfer_interface *xfer, struct uri *uri,
 	if ( ! http )
 		return -ENOMEM;
 	ref_init ( &http->refcnt, http_free );
-	xfer_init ( &http->xfer, &http_xfer_operations, &http->refcnt );
+	intf_init ( &http->xfer, &http_xfer_desc, &http->refcnt );
        	http->uri = uri_get ( uri );
-	xfer_init ( &http->socket, &http_socket_operations, &http->refcnt );
+	intf_init ( &http->socket, &http_socket_desc, &http->refcnt );
 	process_init ( &http->process, http_step, &http->refcnt );
 
 	/* Open socket */
@@ -567,7 +530,7 @@ int http_open_filter ( struct xfer_interface *xfer, struct uri *uri,
 		goto err;
 
 	/* Attach to parent interface, mortalise self, and return */
-	xfer_plug_plug ( &http->xfer, xfer );
+	intf_plug_plug ( &http->xfer, xfer );
 	ref_put ( &http->refcnt );
 	return 0;
 
@@ -586,7 +549,7 @@ int http_open_filter ( struct xfer_interface *xfer, struct uri *uri,
  * @v uri		Uniform Resource Identifier
  * @ret rc		Return status code
  */
-static int http_open ( struct xfer_interface *xfer, struct uri *uri ) {
+static int http_open ( struct interface *xfer, struct uri *uri ) {
 	return http_open_filter ( xfer, uri, HTTP_PORT, NULL );
 }
 
diff --git a/src/net/tcp/https.c b/src/net/tcp/https.c
index b738f4167..805d108bb 100644
--- a/src/net/tcp/https.c
+++ b/src/net/tcp/https.c
@@ -40,7 +40,7 @@ FEATURE ( FEATURE_PROTOCOL, "HTTPS", DHCP_EB_FEATURE_HTTPS, 1 );
  * @v uri		Uniform Resource Identifier
  * @ret rc		Return status code
  */
-static int https_open ( struct xfer_interface *xfer, struct uri *uri ) {
+static int https_open ( struct interface *xfer, struct uri *uri ) {
 	return http_open_filter ( xfer, uri, HTTPS_PORT, add_tls );
 }
 
diff --git a/src/net/tcp/iscsi.c b/src/net/tcp/iscsi.c
index 24cbda2c5..80c63a6b1 100644
--- a/src/net/tcp/iscsi.c
+++ b/src/net/tcp/iscsi.c
@@ -27,6 +27,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #include <byteswap.h>
 #include <ipxe/vsprintf.h>
 #include <ipxe/socket.h>
+#include <ipxe/iobuf.h>
 #include <ipxe/xfer.h>
 #include <ipxe/open.h>
 #include <ipxe/scsi.h>
@@ -199,7 +200,7 @@ static int iscsi_open_connection ( struct iscsi_session *iscsi ) {
 static void iscsi_close_connection ( struct iscsi_session *iscsi, int rc ) {
 
 	/* Close all data transfer interfaces */
-	xfer_close ( &iscsi->socket, rc );
+	intf_restart ( &iscsi->socket, rc );
 
 	/* Clear connection status */
 	iscsi->status = 0;
@@ -1435,9 +1436,9 @@ static int iscsi_rx_data ( struct iscsi_session *iscsi, const void *data,
 /**
  * Receive new data
  *
- * @v socket		Transport layer interface
- * @v data		Received data
- * @v len		Length of received data
+ * @v iscsi		iSCSI session
+ * @v iobuf		I/O buffer
+ * @v meta		Data transfer metadata
  * @ret rc		Return status code
  *
  * This handles received PDUs.  The receive strategy is to fill in
@@ -1447,10 +1448,9 @@ static int iscsi_rx_data ( struct iscsi_session *iscsi, const void *data,
  * always has a full copy of the BHS available, even for portions of
  * the data in different packets to the BHS.
  */
-static int iscsi_socket_deliver_raw ( struct xfer_interface *socket,
-				      const void *data, size_t len ) {
-	struct iscsi_session *iscsi =
-		container_of ( socket, struct iscsi_session, socket );
+static int iscsi_socket_deliver ( struct iscsi_session *iscsi,
+				  struct io_buffer *iobuf,
+				  struct xfer_metadata *meta __unused ) {
 	struct iscsi_bhs_common *common = &iscsi->rx_bhs.common;
 	int ( * rx ) ( struct iscsi_session *iscsi, const void *data,
 		       size_t len, size_t remaining );
@@ -1483,48 +1483,52 @@ static int iscsi_socket_deliver_raw ( struct xfer_interface *socket,
 			break;
 		default:
 			assert ( 0 );
-			return -EINVAL;
+			rc = -EINVAL;
+			goto done;
 		}
 
 		frag_len = iscsi->rx_len - iscsi->rx_offset;
-		if ( frag_len > len )
-			frag_len = len;
+		if ( frag_len > iob_len ( iobuf ) )
+			frag_len = iob_len ( iobuf );
 		remaining = iscsi->rx_len - iscsi->rx_offset - frag_len;
-		if ( ( rc = rx ( iscsi, data, frag_len, remaining ) ) != 0 ) {
+		if ( ( rc = rx ( iscsi, iobuf->data, frag_len,
+				 remaining ) ) != 0 ) {
 			DBGC ( iscsi, "iSCSI %p could not process received "
 			       "data: %s\n", iscsi, strerror ( rc ) );
 			iscsi_close_connection ( iscsi, rc );
 			iscsi_scsi_done ( iscsi, rc );
-			return rc;
+			goto done;
 		}
 
 		iscsi->rx_offset += frag_len;
-		data += frag_len;
-		len -= frag_len;
+		iob_pull ( iobuf, frag_len );
 
 		/* If all the data for this state has not yet been
 		 * received, stay in this state for now.
 		 */
-		if ( iscsi->rx_offset != iscsi->rx_len )
-			return 0;
+		if ( iscsi->rx_offset != iscsi->rx_len ) {
+			rc = 0;
+			goto done;
+		}
 
 		iscsi->rx_state = next_state;
 		iscsi->rx_offset = 0;
 	}
 
-	return 0;
+ done:
+	/* Free I/O buffer */
+	free_iob ( iobuf );
+	return rc;
 }
 
 /**
  * Handle stream connection closure
  *
- * @v socket		Transport layer interface
+ * @v iscsi		iSCSI session
  * @v rc		Reason for close
  *
  */
-static void iscsi_socket_close ( struct xfer_interface *socket, int rc ) {
-	struct iscsi_session *iscsi =
-		container_of ( socket, struct iscsi_session, socket );
+static void iscsi_socket_close ( struct iscsi_session *iscsi, int rc ) {
 
 	/* Even a graceful close counts as an error for iSCSI */
 	if ( ! rc )
@@ -1552,15 +1556,13 @@ static void iscsi_socket_close ( struct xfer_interface *socket, int rc ) {
 /**
  * Handle redirection event
  *
- * @v socket		Transport layer interface
+ * @v iscsi		iSCSI session
  * @v type		Location type
  * @v args		Remaining arguments depend upon location type
  * @ret rc		Return status code
  */
-static int iscsi_vredirect ( struct xfer_interface *socket, int type,
+static int iscsi_vredirect ( struct iscsi_session *iscsi, int type,
 			     va_list args ) {
-	struct iscsi_session *iscsi =
-		container_of ( socket, struct iscsi_session, socket );
 	va_list tmp;
 	struct sockaddr *peer;
 
@@ -1578,20 +1580,20 @@ static int iscsi_vredirect ( struct xfer_interface *socket, int type,
 		va_end ( tmp );
 	}
 
-	return xfer_vreopen ( socket, type, args );
+	return xfer_vreopen ( &iscsi->socket, type, args );
 }
 			     
 
-/** iSCSI socket operations */
-static struct xfer_interface_operations iscsi_socket_operations = {
-	.close		= iscsi_socket_close,
-	.vredirect	= iscsi_vredirect,
-	.window		= unlimited_xfer_window,
-	.alloc_iob	= default_xfer_alloc_iob,
-	.deliver_iob	= xfer_deliver_as_raw,
-	.deliver_raw	= iscsi_socket_deliver_raw,
+/** iSCSI socket interface operations */
+static struct interface_operation iscsi_socket_operations[] = {
+	INTF_OP ( xfer_deliver, struct iscsi_session *, iscsi_socket_deliver ),
+	INTF_OP ( xfer_vredirect, struct iscsi_session *, iscsi_vredirect ),
+	INTF_OP ( intf_close, struct iscsi_session *, iscsi_socket_close ),
 };
 
+/** iSCSI socket interface descriptor */
+static struct interface_descriptor iscsi_socket_desc =
+	INTF_DESC ( struct iscsi_session, socket, iscsi_socket_operations );
 
 /****************************************************************************
  *
@@ -1641,7 +1643,6 @@ void iscsi_detach ( struct scsi_device *scsi ) {
 	struct iscsi_session *iscsi =
 		container_of ( scsi->backend, struct iscsi_session, refcnt );
 
-	xfer_nullify ( &iscsi->socket );
 	iscsi_close_connection ( iscsi, 0 );
 	process_del ( &iscsi->process );
 	scsi->command = scsi_detached_command;
@@ -1793,7 +1794,7 @@ int iscsi_attach ( struct scsi_device *scsi, const char *root_path ) {
 	if ( ! iscsi )
 		return -ENOMEM;
 	ref_init ( &iscsi->refcnt, iscsi_free );
-	xfer_init ( &iscsi->socket, &iscsi_socket_operations, &iscsi->refcnt );
+	intf_init ( &iscsi->socket, &iscsi_socket_desc, &iscsi->refcnt );
 	process_init ( &iscsi->process, iscsi_tx_step, &iscsi->refcnt );
 
 	/* Parse root path */
diff --git a/src/net/tls.c b/src/net/tls.c
index 8825c5c13..a9d627588 100644
--- a/src/net/tls.c
+++ b/src/net/tls.c
@@ -35,9 +35,9 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #include <ipxe/sha1.h>
 #include <ipxe/aes.h>
 #include <ipxe/rsa.h>
+#include <ipxe/iobuf.h>
 #include <ipxe/xfer.h>
 #include <ipxe/open.h>
-#include <ipxe/filter.h>
 #include <ipxe/asn1.h>
 #include <ipxe/x509.h>
 #include <ipxe/tls.h>
@@ -107,10 +107,8 @@ static void tls_close ( struct tls_session *tls, int rc ) {
 	process_del ( &tls->process );
 	
 	/* Close ciphertext and plaintext streams */
-	xfer_nullify ( &tls->cipherstream.xfer );
-	xfer_close ( &tls->cipherstream.xfer, rc );
-	xfer_nullify ( &tls->plainstream.xfer );
-	xfer_close ( &tls->plainstream.xfer, rc );
+	intf_shutdown ( &tls->cipherstream, rc );
+	intf_shutdown ( &tls->plainstream, rc );
 }
 
 /******************************************************************************
@@ -1030,7 +1028,7 @@ static int tls_new_record ( struct tls_session *tls,
 	case TLS_TYPE_HANDSHAKE:
 		return tls_new_handshake ( tls, data, len );
 	case TLS_TYPE_DATA:
-		return xfer_deliver_raw ( &tls->plainstream.xfer, data, len );
+		return xfer_deliver_raw ( &tls->plainstream, data, len );
 	default:
 		/* RFC4346 says that we should just ignore unknown
 		 * record types.
@@ -1209,8 +1207,7 @@ static int tls_send_plaintext ( struct tls_session *tls, unsigned int type,
 
 	/* Allocate ciphertext */
 	ciphertext_len = ( sizeof ( *tlshdr ) + plaintext_len );
-	ciphertext = xfer_alloc_iob ( &tls->cipherstream.xfer,
-				      ciphertext_len );
+	ciphertext = xfer_alloc_iob ( &tls->cipherstream, ciphertext_len );
 	if ( ! ciphertext ) {
 		DBGC ( tls, "TLS %p could not allocate %zd bytes for "
 		       "ciphertext\n", tls, ciphertext_len );
@@ -1234,9 +1231,8 @@ static int tls_send_plaintext ( struct tls_session *tls, unsigned int type,
 	plaintext = NULL;
 
 	/* Send ciphertext */
-	rc = xfer_deliver_iob ( &tls->cipherstream.xfer, ciphertext );
-	ciphertext = NULL;
-	if ( rc != 0 ) {
+	if ( ( rc = xfer_deliver_iob ( &tls->cipherstream,
+				       iob_disown ( ciphertext ) ) ) != 0 ) {
 		DBGC ( tls, "TLS %p could not deliver ciphertext: %s\n",
 		       tls, strerror ( rc ) );
 		goto done;
@@ -1436,65 +1432,60 @@ static int tls_new_ciphertext ( struct tls_session *tls,
  */
 
 /**
- * Close interface
- *
- * @v xfer		Plainstream data transfer interface
- * @v rc		Reason for close
- */
-static void tls_plainstream_close ( struct xfer_interface *xfer, int rc ) {
-	struct tls_session *tls =
-		container_of ( xfer, struct tls_session, plainstream.xfer );
-
-	tls_close ( tls, rc );
-}
-
-/**
  * Check flow control window
  *
- * @v xfer		Plainstream data transfer interface
+ * @v tls		TLS session
  * @ret len		Length of window
  */
-static size_t tls_plainstream_window ( struct xfer_interface *xfer ) {
-	struct tls_session *tls =
-		container_of ( xfer, struct tls_session, plainstream.xfer );
+static size_t tls_plainstream_window ( struct tls_session *tls ) {
 
 	/* Block window unless we are ready to accept data */
 	if ( tls->tx_state != TLS_TX_DATA )
 		return 0;
 
-	return filter_window ( xfer );
+	return xfer_window ( &tls->cipherstream );
 }
 
 /**
  * Deliver datagram as raw data
  *
- * @v xfer		Plainstream data transfer interface
- * @v data		Data buffer
- * @v len		Length of data buffer
+ * @v tls		TLS session
+ * @v iobuf		I/O buffer
+ * @v meta		Data transfer metadata
  * @ret rc		Return status code
  */
-static int tls_plainstream_deliver_raw ( struct xfer_interface *xfer,
-					 const void *data, size_t len ) {
-	struct tls_session *tls =
-		container_of ( xfer, struct tls_session, plainstream.xfer );
+static int tls_plainstream_deliver ( struct tls_session *tls,
+				     struct io_buffer *iobuf,
+				     struct xfer_metadata *meta __unused ) {
+	int rc;
 	
 	/* Refuse unless we are ready to accept data */
-	if ( tls->tx_state != TLS_TX_DATA )
-		return -ENOTCONN;
+	if ( tls->tx_state != TLS_TX_DATA ) {
+		rc = -ENOTCONN;
+		goto done;
+	}
+
+	if ( ( rc = tls_send_plaintext ( tls, TLS_TYPE_DATA, iobuf->data,
+					 iob_len ( iobuf ) ) ) != 0 )
+		goto done;
 
-	return tls_send_plaintext ( tls, TLS_TYPE_DATA, data, len );
+ done:
+	free_iob ( iobuf );
+	return rc;
 }
 
-/** TLS plaintext stream operations */
-static struct xfer_interface_operations tls_plainstream_operations = {
-	.close		= tls_plainstream_close,
-	.vredirect	= ignore_xfer_vredirect,
-	.window		= tls_plainstream_window,
-	.alloc_iob	= default_xfer_alloc_iob,
-	.deliver_iob	= xfer_deliver_as_raw,
-	.deliver_raw	= tls_plainstream_deliver_raw,
+/** TLS plaintext stream interface operations */
+static struct interface_operation tls_plainstream_ops[] = {
+	INTF_OP ( xfer_deliver, struct tls_session *, tls_plainstream_deliver ),
+	INTF_OP ( xfer_window, struct tls_session *, tls_plainstream_window ),
+	INTF_OP ( intf_close, struct tls_session *, tls_close ),
 };
 
+/** TLS plaintext stream interface descriptor */
+static struct interface_descriptor tls_plainstream_desc =
+	INTF_DESC_PASSTHRU ( struct tls_session, plainstream,
+			     tls_plainstream_ops, cipherstream );
+
 /******************************************************************************
  *
  * Ciphertext stream operations
@@ -1503,19 +1494,6 @@ static struct xfer_interface_operations tls_plainstream_operations = {
  */
 
 /**
- * Close interface
- *
- * @v xfer		Plainstream data transfer interface
- * @v rc		Reason for close
- */
-static void tls_cipherstream_close ( struct xfer_interface *xfer, int rc ) {
-	struct tls_session *tls =
-		container_of ( xfer, struct tls_session, cipherstream.xfer );
-
-	tls_close ( tls, rc );
-}
-
-/**
  * Handle received TLS header
  *
  * @v tls		TLS session
@@ -1569,22 +1547,21 @@ static int tls_newdata_process_data ( struct tls_session *tls ) {
 /**
  * Receive new ciphertext
  *
- * @v app		Stream application
- * @v data		Data received
- * @v len		Length of received data
+ * @v tls		TLS session
+ * @v iobuf		I/O buffer
+ * @v meta		Data transfer metadat
  * @ret rc		Return status code
  */
-static int tls_cipherstream_deliver_raw ( struct xfer_interface *xfer,
-					  const void *data, size_t len ) {
-	struct tls_session *tls = 
-		container_of ( xfer, struct tls_session, cipherstream.xfer );
+static int tls_cipherstream_deliver ( struct tls_session *tls,
+				      struct io_buffer *iobuf,
+				      struct xfer_metadata *xfer __unused ) {
 	size_t frag_len;
 	void *buf;
 	size_t buf_len;
 	int ( * process ) ( struct tls_session *tls );
 	int rc;
 
-	while ( len ) {
+	while ( iob_len ( iobuf ) ) {
 		/* Select buffer according to current state */
 		switch ( tls->rx_state ) {
 		case TLS_RX_HEADER:
@@ -1599,41 +1576,46 @@ static int tls_cipherstream_deliver_raw ( struct xfer_interface *xfer,
 			break;
 		default:
 			assert ( 0 );
-			return -EINVAL;
+			rc = -EINVAL;
+			goto done;
 		}
 
 		/* Copy data portion to buffer */
 		frag_len = ( buf_len - tls->rx_rcvd );
-		if ( frag_len > len )
-			frag_len = len;
-		memcpy ( ( buf + tls->rx_rcvd ), data, frag_len );
+		if ( frag_len > iob_len  ( iobuf ) )
+			frag_len = iob_len ( iobuf );
+		memcpy ( ( buf + tls->rx_rcvd ), iobuf->data, frag_len );
 		tls->rx_rcvd += frag_len;
-		data += frag_len;
-		len -= frag_len;
+		iob_pull ( iobuf, frag_len );
 
 		/* Process data if buffer is now full */
 		if ( tls->rx_rcvd == buf_len ) {
 			if ( ( rc = process ( tls ) ) != 0 ) {
 				tls_close ( tls, rc );
-				return rc;
+				goto done;
 			}
 			tls->rx_rcvd = 0;
 		}
 	}
+	rc = 0;
 
-	return 0;
+ done:
+	free_iob ( iobuf );
+	return rc;
 }
 
-/** TLS ciphertext stream operations */
-static struct xfer_interface_operations tls_cipherstream_operations = {
-	.close		= tls_cipherstream_close,
-	.vredirect	= xfer_vreopen,
-	.window		= filter_window,
-	.alloc_iob	= default_xfer_alloc_iob,
-	.deliver_iob	= xfer_deliver_as_raw,
-	.deliver_raw	= tls_cipherstream_deliver_raw,
+/** TLS ciphertext stream interface operations */
+static struct interface_operation tls_cipherstream_ops[] = {
+	INTF_OP ( xfer_deliver, struct tls_session *,
+		  tls_cipherstream_deliver ),
+	INTF_OP ( intf_close, struct tls_session *, tls_close ),
 };
 
+/** TLS ciphertext stream interface descriptor */
+static struct interface_descriptor tls_cipherstream_desc =
+	INTF_DESC_PASSTHRU ( struct tls_session, cipherstream,
+			     tls_cipherstream_ops, plainstream );
+
 /******************************************************************************
  *
  * Controlling process
@@ -1652,7 +1634,7 @@ static void tls_step ( struct process *process ) {
 	int rc;
 
 	/* Wait for cipherstream to become ready */
-	if ( ! xfer_window ( &tls->cipherstream.xfer ) )
+	if ( ! xfer_window ( &tls->cipherstream ) )
 		return;
 
 	switch ( tls->tx_state ) {
@@ -1723,7 +1705,7 @@ static void tls_step ( struct process *process ) {
  ******************************************************************************
  */
 
-int add_tls ( struct xfer_interface *xfer, struct xfer_interface **next ) {
+int add_tls ( struct interface *xfer, struct interface **next ) {
 	struct tls_session *tls;
 
 	/* Allocate and initialise TLS structure */
@@ -1732,9 +1714,8 @@ int add_tls ( struct xfer_interface *xfer, struct xfer_interface **next ) {
 		return -ENOMEM;
 	memset ( tls, 0, sizeof ( *tls ) );
 	ref_init ( &tls->refcnt, free_tls );
-	filter_init ( &tls->plainstream, &tls_plainstream_operations,
-		      &tls->cipherstream, &tls_cipherstream_operations,
-		      &tls->refcnt );
+	intf_init ( &tls->plainstream, &tls_plainstream_desc, &tls->refcnt );
+	intf_init ( &tls->cipherstream, &tls_cipherstream_desc, &tls->refcnt );
 	tls_clear_cipher ( tls, &tls->tx_cipherspec );
 	tls_clear_cipher ( tls, &tls->tx_cipherspec_pending );
 	tls_clear_cipher ( tls, &tls->rx_cipherspec );
@@ -1751,9 +1732,8 @@ int add_tls ( struct xfer_interface *xfer, struct xfer_interface **next ) {
 	process_init ( &tls->process, tls_step, &tls->refcnt );
 
 	/* Attach to parent interface, mortalise self, and return */
-	xfer_plug_plug ( &tls->plainstream.xfer, xfer );
-	*next = &tls->cipherstream.xfer;
+	intf_plug_plug ( &tls->plainstream, xfer );
+	*next = &tls->cipherstream;
 	ref_put ( &tls->refcnt );
 	return 0;
 }
-
diff --git a/src/net/udp.c b/src/net/udp.c
index dcc69c36c..0ed1503a2 100644
--- a/src/net/udp.c
+++ b/src/net/udp.c
@@ -29,7 +29,7 @@ struct udp_connection {
 	struct list_head list;
 
 	/** Data transfer interface */
-	struct xfer_interface xfer;
+	struct interface xfer;
 
 	/** Local socket address */
 	struct sockaddr_tcpip local;
@@ -43,7 +43,7 @@ struct udp_connection {
 static LIST_HEAD ( udp_conns );
 
 /* Forward declatations */
-static struct xfer_interface_operations udp_xfer_operations;
+static struct interface_descriptor udp_xfer_desc;
 struct tcpip_protocol udp_protocol;
 
 /**
@@ -97,7 +97,7 @@ static int udp_bind ( struct udp_connection *udp ) {
  * @v promisc		Socket is promiscuous
  * @ret rc		Return status code
  */
-static int udp_open_common ( struct xfer_interface *xfer,
+static int udp_open_common ( struct interface *xfer,
 			     struct sockaddr *peer, struct sockaddr *local,
 			     int promisc ) {
 	struct sockaddr_tcpip *st_peer = ( struct sockaddr_tcpip * ) peer;
@@ -111,7 +111,7 @@ static int udp_open_common ( struct xfer_interface *xfer,
 		return -ENOMEM;
 	DBGC ( udp, "UDP %p allocated\n", udp );
 	ref_init ( &udp->refcnt, NULL );
-	xfer_init ( &udp->xfer, &udp_xfer_operations, &udp->refcnt );
+	intf_init ( &udp->xfer, &udp_xfer_desc, &udp->refcnt );
 	if ( st_peer )
 		memcpy ( &udp->peer, st_peer, sizeof ( udp->peer ) );
 	if ( st_local )
@@ -126,7 +126,7 @@ static int udp_open_common ( struct xfer_interface *xfer,
 	/* Attach parent interface, transfer reference to connection
 	 * list and return
 	 */
-	xfer_plug_plug ( &udp->xfer, xfer );
+	intf_plug_plug ( &udp->xfer, xfer );
 	list_add ( &udp->list, &udp_conns );
 	return 0;
 
@@ -143,7 +143,7 @@ static int udp_open_common ( struct xfer_interface *xfer,
  * @v local		Local socket address, or NULL
  * @ret rc		Return status code
  */
-int udp_open ( struct xfer_interface *xfer, struct sockaddr *peer,
+int udp_open ( struct interface *xfer, struct sockaddr *peer,
 	       struct sockaddr *local ) {
 	return udp_open_common ( xfer, peer, local, 0 );
 }
@@ -157,7 +157,7 @@ int udp_open ( struct xfer_interface *xfer, struct sockaddr *peer,
  * Promiscuous UDP connections are required in order to support the
  * PXE API.
  */
-int udp_open_promisc ( struct xfer_interface *xfer ) {
+int udp_open_promisc ( struct interface *xfer ) {
 	return udp_open_common ( xfer, NULL, NULL, 1 );
 }
 
@@ -170,8 +170,7 @@ int udp_open_promisc ( struct xfer_interface *xfer ) {
 static void udp_close ( struct udp_connection *udp, int rc ) {
 
 	/* Close data transfer interface */
-	xfer_nullify ( &udp->xfer );
-	xfer_close ( &udp->xfer, rc );
+	intf_shutdown ( &udp->xfer, rc );
 
 	/* Remove from list of connections and drop list's reference */
 	list_del ( &udp->list );
@@ -331,7 +330,7 @@ static int udp_rx ( struct io_buffer *iobuf, struct sockaddr_tcpip *st_src,
 	memset ( &meta, 0, sizeof ( meta ) );
 	meta.src = ( struct sockaddr * ) st_src;
 	meta.dest = ( struct sockaddr * ) st_dest;
-	rc = xfer_deliver_iob_meta ( &udp->xfer, iob_disown ( iobuf ), &meta );
+	rc = xfer_deliver ( &udp->xfer, iob_disown ( iobuf ), &meta );
 
  done:
 	free_iob ( iobuf );
@@ -352,30 +351,14 @@ struct tcpip_protocol udp_protocol __tcpip_protocol = {
  */
 
 /**
- * Close interface
- *
- * @v xfer		Data transfer interface
- * @v rc		Reason for close
- */
-static void udp_xfer_close ( struct xfer_interface *xfer, int rc ) {
-	struct udp_connection *udp =
-		container_of ( xfer, struct udp_connection, xfer );
-
-	/* Close connection */
-	udp_close ( udp, rc );
-}
-
-/**
  * Allocate I/O buffer for UDP
  *
- * @v xfer		Data transfer interface
+ * @v udp		UDP connection
  * @v len		Payload size
  * @ret iobuf		I/O buffer, or NULL
  */
-static struct io_buffer * udp_alloc_iob ( struct xfer_interface *xfer,
-					  size_t len ) {
-	struct udp_connection *udp =
-		container_of ( xfer, struct udp_connection, xfer );	
+static struct io_buffer * udp_xfer_alloc_iob ( struct udp_connection *udp,
+					       size_t len ) {
 	struct io_buffer *iobuf;
 
 	iobuf = alloc_iob ( UDP_MAX_HLEN + len );
@@ -391,16 +374,14 @@ static struct io_buffer * udp_alloc_iob ( struct xfer_interface *xfer,
 /**
  * Deliver datagram as I/O buffer
  *
- * @v xfer		Data transfer interface
+ * @v udp		UDP connection
  * @v iobuf		Datagram I/O buffer
  * @v meta		Data transfer metadata
  * @ret rc		Return status code
  */
-static int udp_xfer_deliver_iob ( struct xfer_interface *xfer,
-				  struct io_buffer *iobuf,
-				  struct xfer_metadata *meta ) {
-	struct udp_connection *udp =
-		container_of ( xfer, struct udp_connection, xfer );
+static int udp_xfer_deliver ( struct udp_connection *udp,
+			      struct io_buffer *iobuf,
+			      struct xfer_metadata *meta ) {
 
 	/* Transmit data, if possible */
 	udp_tx ( udp, iobuf, ( ( struct sockaddr_tcpip * ) meta->src ),
@@ -410,15 +391,16 @@ static int udp_xfer_deliver_iob ( struct xfer_interface *xfer,
 }
 
 /** UDP data transfer interface operations */
-static struct xfer_interface_operations udp_xfer_operations = {
-	.close		= udp_xfer_close,
-	.vredirect	= ignore_xfer_vredirect,
-	.window		= unlimited_xfer_window,
-	.alloc_iob	= udp_alloc_iob,
-	.deliver_iob	= udp_xfer_deliver_iob,
-	.deliver_raw	= xfer_deliver_as_iob,
+static struct interface_operation udp_xfer_operations[] = {
+	INTF_OP ( xfer_deliver, struct udp_connection *, udp_xfer_deliver ),
+	INTF_OP ( xfer_alloc_iob, struct udp_connection *, udp_xfer_alloc_iob ),
+	INTF_OP ( intf_close, struct udp_connection *, udp_close ),
 };
 
+/** UDP data transfer interface descriptor */
+static struct interface_descriptor udp_xfer_desc =
+	INTF_DESC ( struct udp_connection, xfer, udp_xfer_operations );
+
 /***************************************************************************
  *
  * Openers
@@ -443,7 +425,7 @@ int udp_sock_dgram = UDP_SOCK_DGRAM;
  * @v uri		URI
  * @ret rc		Return status code
  */
-static int udp_open_uri ( struct xfer_interface *xfer, struct uri *uri ) {
+static int udp_open_uri ( struct interface *xfer, struct uri *uri ) {
 	struct sockaddr_tcpip peer;
 
 	/* Sanity check */
diff --git a/src/net/udp/dhcp.c b/src/net/udp/dhcp.c
index 991983197..fb62bef53 100644
--- a/src/net/udp/dhcp.c
+++ b/src/net/udp/dhcp.c
@@ -26,6 +26,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #include <assert.h>
 #include <byteswap.h>
 #include <ipxe/if_ether.h>
+#include <ipxe/iobuf.h>
 #include <ipxe/netdevice.h>
 #include <ipxe/device.h>
 #include <ipxe/xfer.h>
@@ -240,7 +241,7 @@ struct dhcp_session {
 	/** Job control interface */
 	struct interface job;
 	/** Data transfer interface */
-	struct xfer_interface xfer;
+	struct interface xfer;
 
 	/** Network device being configured */
 	struct net_device *netdev;
@@ -298,8 +299,7 @@ static void dhcp_finished ( struct dhcp_session *dhcp, int rc ) {
 	stop_timer ( &dhcp->timer );
 
 	/* Shut down interfaces */
-	xfer_nullify ( &dhcp->xfer );
-	xfer_close ( &dhcp->xfer, rc );
+	intf_shutdown ( &dhcp->xfer, rc );
 	intf_shutdown ( &dhcp->job, rc );
 }
 
@@ -1241,8 +1241,8 @@ static int dhcp_tx ( struct dhcp_session *dhcp ) {
 
 	/* Transmit the packet */
 	iob_put ( iobuf, dhcppkt.len );
-	if ( ( rc = xfer_deliver_iob_meta ( &dhcp->xfer, iob_disown ( iobuf ),
-					    &meta ) ) != 0 ) {
+	if ( ( rc = xfer_deliver ( &dhcp->xfer, iob_disown ( iobuf ),
+				   &meta ) ) != 0 ) {
 		DBGC ( dhcp, "DHCP %p could not transmit UDP packet: %s\n",
 		       dhcp, strerror ( rc ) );
 		goto done;
@@ -1256,16 +1256,14 @@ static int dhcp_tx ( struct dhcp_session *dhcp ) {
 /**
  * Receive new data
  *
- * @v xfer 		Data transfer interface
+ * @v dhcp		DHCP session
  * @v iobuf		I/O buffer
  * @v meta		Transfer metadata
  * @ret rc		Return status code
  */
-static int dhcp_deliver_iob ( struct xfer_interface *xfer,
-			      struct io_buffer *iobuf,
-			      struct xfer_metadata *meta ) {
-	struct dhcp_session *dhcp =
-		container_of ( xfer, struct dhcp_session, xfer );
+static int dhcp_deliver ( struct dhcp_session *dhcp,
+			  struct io_buffer *iobuf,
+			  struct xfer_metadata *meta ) {
 	struct sockaddr_in *peer;
 	size_t data_len;
 	struct dhcp_packet *dhcppkt;
@@ -1328,15 +1326,14 @@ static int dhcp_deliver_iob ( struct xfer_interface *xfer,
 }
 
 /** DHCP data transfer interface operations */
-static struct xfer_interface_operations dhcp_xfer_operations = {
-	.close		= ignore_xfer_close,
-	.vredirect	= xfer_vreopen,
-	.window		= unlimited_xfer_window,
-	.alloc_iob	= default_xfer_alloc_iob,
-	.deliver_iob	= dhcp_deliver_iob,
-	.deliver_raw	= xfer_deliver_as_iob,
+static struct interface_operation dhcp_xfer_operations[] = {
+	INTF_OP ( xfer_deliver, struct dhcp_session *, dhcp_deliver ),
 };
 
+/** DHCP data transfer interface descriptor */
+static struct interface_descriptor dhcp_xfer_desc =
+	INTF_DESC ( struct dhcp_session, xfer, dhcp_xfer_operations );
+
 /**
  * Handle DHCP retry timer expiry
  *
@@ -1427,7 +1424,7 @@ int start_dhcp ( struct interface *job, struct net_device *netdev ) {
 		return -ENOMEM;
 	ref_init ( &dhcp->refcnt, dhcp_free );
 	intf_init ( &dhcp->job, &dhcp_job_desc, &dhcp->refcnt );
-	xfer_init ( &dhcp->xfer, &dhcp_xfer_operations, &dhcp->refcnt );
+	intf_init ( &dhcp->xfer, &dhcp_xfer_desc, &dhcp->refcnt );
 	timer_init ( &dhcp->timer, dhcp_timer_expired );
 	dhcp->netdev = netdev_get ( netdev );
 	dhcp->local.sin_family = AF_INET;
@@ -1530,7 +1527,7 @@ int start_pxebs ( struct interface *job, struct net_device *netdev,
 		return -ENOMEM;
 	ref_init ( &dhcp->refcnt, dhcp_free );
 	intf_init ( &dhcp->job, &dhcp_job_desc, &dhcp->refcnt );
-	xfer_init ( &dhcp->xfer, &dhcp_xfer_operations, &dhcp->refcnt );
+	intf_init ( &dhcp->xfer, &dhcp_xfer_desc, &dhcp->refcnt );
 	timer_init ( &dhcp->timer, dhcp_timer_expired );
 	dhcp->netdev = netdev_get ( netdev );
 	dhcp->local.sin_family = AF_INET;
diff --git a/src/net/udp/dns.c b/src/net/udp/dns.c
index fd1ea0a28..8283e6fba 100644
--- a/src/net/udp/dns.c
+++ b/src/net/udp/dns.c
@@ -28,6 +28,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #include <errno.h>
 #include <byteswap.h>
 #include <ipxe/refcnt.h>
+#include <ipxe/iobuf.h>
 #include <ipxe/xfer.h>
 #include <ipxe/open.h>
 #include <ipxe/resolv.h>
@@ -60,7 +61,7 @@ struct dns_request {
 	/** Name resolution interface */
 	struct interface resolv;
 	/** Data transfer interface */
-	struct xfer_interface socket;
+	struct interface socket;
 	/** Retry timer */
 	struct retry_timer timer;
 
@@ -89,11 +90,8 @@ static void dns_done ( struct dns_request *dns, int rc ) {
 	/* Stop the retry timer */
 	stop_timer ( &dns->timer );
 
-	/* Close data transfer interface */
-	xfer_nullify ( &dns->socket );
-	xfer_close ( &dns->socket, rc );
-
 	/* Shut down interfaces */
+	intf_shutdown ( &dns->socket, rc );
 	intf_shutdown ( &dns->resolv, rc );
 }
 
@@ -322,25 +320,26 @@ static void dns_timer_expired ( struct retry_timer *timer, int fail ) {
 /**
  * Receive new data
  *
- * @v socket		UDP socket
- * @v data		DNS reply
- * @v len		Length of DNS reply
+ * @v dns		DNS request
+ * @v iobuf		I/O buffer
+ * @v meta		Data transfer metadata
  * @ret rc		Return status code
  */
-static int dns_xfer_deliver_raw ( struct xfer_interface *socket,
-				  const void *data, size_t len ) {
-	struct dns_request *dns =
-		container_of ( socket, struct dns_request, socket );
-	const struct dns_header *reply = data;
+static int dns_xfer_deliver ( struct dns_request *dns,
+			      struct io_buffer *iobuf,
+			      struct xfer_metadata *meta __unused ) {
+	const struct dns_header *reply = iobuf->data;
 	union dns_rr_info *rr_info;
 	struct sockaddr_in *sin;
 	unsigned int qtype = dns->qinfo->qtype;
+	int rc;
 
 	/* Sanity check */
-	if ( len < sizeof ( *reply ) ) {
+	if ( iob_len ( iobuf ) < sizeof ( *reply ) ) {
 		DBGC ( dns, "DNS %p received underlength packet length %zd\n",
-		       dns, len );
-		return -EINVAL;
+		       dns, iob_len ( iobuf ) );
+		rc = -EINVAL;
+		goto done;
 	}
 
 	/* Check reply ID matches query ID */
@@ -348,7 +347,8 @@ static int dns_xfer_deliver_raw ( struct xfer_interface *socket,
 		DBGC ( dns, "DNS %p received unexpected reply ID %d "
 		       "(wanted %d)\n", dns, ntohs ( reply->id ),
 		       ntohs ( dns->query.dns.id ) );
-		return -EINVAL;
+		rc = -EINVAL;
+		goto done;
 	}
 
 	DBGC ( dns, "DNS %p received reply ID %d\n", dns, ntohs ( reply->id ));
@@ -382,7 +382,8 @@ static int dns_xfer_deliver_raw ( struct xfer_interface *socket,
 
 			/* Mark operation as complete */
 			dns_done ( dns, 0 );
-			return 0;
+			rc = 0;
+			goto done;
 
 		case htons ( DNS_TYPE_CNAME ):
 
@@ -399,7 +400,8 @@ static int dns_xfer_deliver_raw ( struct xfer_interface *socket,
 				DBGC ( dns, "DNS %p recursion exceeded\n",
 				       dns );
 				dns_done ( dns, -ELOOP );
-				return 0;
+				rc = 0;
+				goto done;
 			}
 			break;
 
@@ -422,7 +424,8 @@ static int dns_xfer_deliver_raw ( struct xfer_interface *socket,
 		DBGC ( dns, "DNS %p found no A record; trying CNAME\n", dns );
 		dns->qinfo->qtype = htons ( DNS_TYPE_CNAME );
 		dns_send_packet ( dns );
-		return 0;
+		rc = 0;
+		goto done;
 
 	case htons ( DNS_TYPE_CNAME ):
 		/* We asked for a CNAME record.  If we got a response
@@ -431,29 +434,35 @@ static int dns_xfer_deliver_raw ( struct xfer_interface *socket,
 		 */
 		if ( dns->qinfo->qtype == htons ( DNS_TYPE_A ) ) {
 			dns_send_packet ( dns );
-			return 0;
+			rc = 0;
+			goto done;
 		} else {
 			DBGC ( dns, "DNS %p found no CNAME record\n", dns );
 			dns_done ( dns, -ENXIO );
-			return 0;
+			rc = 0;
+			goto done;
 		}
 
 	default:
 		assert ( 0 );
 		dns_done ( dns, -EINVAL );
-		return 0;
+		rc = -EINVAL;
+		goto done;
 	}
+
+ done:
+	/* Free I/O buffer */
+	free_iob ( iobuf );
+	return rc;
 }
 
 /**
  * Receive new data
  *
- * @v socket		UDP socket
+ * @v dns		DNS request
  * @v rc		Reason for close
  */
-static void dns_xfer_close ( struct xfer_interface *socket, int rc ) {
-	struct dns_request *dns =
-		container_of ( socket, struct dns_request, socket );
+static void dns_xfer_close ( struct dns_request *dns, int rc ) {
 
 	if ( ! rc )
 		rc = -ECONNABORTED;
@@ -461,16 +470,16 @@ static void dns_xfer_close ( struct xfer_interface *socket, int rc ) {
 	dns_done ( dns, rc );
 }
 
-/** DNS socket operations */
-static struct xfer_interface_operations dns_socket_operations = {
-	.close		= dns_xfer_close,
-	.vredirect	= xfer_vreopen,
-	.window		= unlimited_xfer_window,
-	.alloc_iob	= default_xfer_alloc_iob,
-	.deliver_iob	= xfer_deliver_as_raw,
-	.deliver_raw	= dns_xfer_deliver_raw,
+/** DNS socket interface operations */
+static struct interface_operation dns_socket_operations[] = {
+	INTF_OP ( xfer_deliver, struct dns_request *, dns_xfer_deliver ),
+	INTF_OP ( intf_close, struct dns_request *, dns_xfer_close ),
 };
 
+/** DNS socket interface descriptor */
+static struct interface_descriptor dns_socket_desc =
+	INTF_DESC ( struct dns_request, socket, dns_socket_operations );
+
 /** DNS resolver interface operations */
 static struct interface_operation dns_resolv_op[] = {
 	INTF_OP ( intf_close, struct dns_request *, dns_done ),
@@ -517,7 +526,7 @@ static int dns_resolv ( struct interface *resolv,
 	}
 	ref_init ( &dns->refcnt, NULL );
 	intf_init ( &dns->resolv, &dns_resolv_desc, &dns->refcnt );
-	xfer_init ( &dns->socket, &dns_socket_operations, &dns->refcnt );
+	intf_init ( &dns->socket, &dns_socket_desc, &dns->refcnt );
 	timer_init ( &dns->timer, dns_timer_expired );
 	memcpy ( &dns->sa, sa, sizeof ( dns->sa ) );
 
diff --git a/src/net/udp/slam.c b/src/net/udp/slam.c
index a5a2421fa..84bb9cba3 100644
--- a/src/net/udp/slam.c
+++ b/src/net/udp/slam.c
@@ -119,11 +119,11 @@ struct slam_request {
 	struct refcnt refcnt;
 
 	/** Data transfer interface */
-	struct xfer_interface xfer;
+	struct interface xfer;
 	/** Unicast socket */
-	struct xfer_interface socket;
+	struct interface socket;
 	/** Multicast socket */
-	struct xfer_interface mc_socket;
+	struct interface mc_socket;
 
 	/** Master client retry timer */
 	struct retry_timer master_timer;
@@ -184,12 +184,9 @@ static void slam_finished ( struct slam_request *slam, int rc ) {
 	stop_timer ( &slam->slave_timer );
 
 	/* Close all data transfer interfaces */
-	xfer_nullify ( &slam->socket );
-	xfer_close ( &slam->socket, rc );
-	xfer_nullify ( &slam->mc_socket );
-	xfer_close ( &slam->mc_socket, rc );
-	xfer_nullify ( &slam->xfer );
-	xfer_close ( &slam->xfer, rc );
+	intf_shutdown ( &slam->socket, rc );
+	intf_shutdown ( &slam->mc_socket, rc );
+	intf_shutdown ( &slam->xfer, rc );
 }
 
 /****************************************************************************
@@ -473,15 +470,13 @@ static int slam_pull_header ( struct slam_request *slam,
 /**
  * Receive SLAM data packet
  *
- * @v mc_socket		SLAM multicast socket
+ * @v slam		SLAM request
  * @v iobuf		I/O buffer
  * @ret rc		Return status code
  */
-static int slam_mc_socket_deliver ( struct xfer_interface *mc_socket,
+static int slam_mc_socket_deliver ( struct slam_request *slam,
 				    struct io_buffer *iobuf,
 				    struct xfer_metadata *rx_meta __unused ) {
-	struct slam_request *slam =
-		container_of ( mc_socket, struct slam_request, mc_socket );
 	struct xfer_metadata meta;
 	unsigned long packet;
 	size_t len;
@@ -533,8 +528,7 @@ static int slam_mc_socket_deliver ( struct xfer_interface *mc_socket,
 	memset ( &meta, 0, sizeof ( meta ) );
 	meta.whence = SEEK_SET;
 	meta.offset = ( packet * slam->block_size );
-	if ( ( rc = xfer_deliver_iob_meta ( &slam->xfer, iobuf,
-					    &meta ) ) != 0 )
+	if ( ( rc = xfer_deliver ( &slam->xfer, iobuf, &meta ) ) != 0 )
 		goto err;
 
 	/* Mark block as received */
@@ -556,15 +550,13 @@ static int slam_mc_socket_deliver ( struct xfer_interface *mc_socket,
 /**
  * Receive SLAM non-data packet
  *
- * @v socket		SLAM unicast socket
+ * @v slam		SLAM request
  * @v iobuf		I/O buffer
  * @ret rc		Return status code
  */
-static int slam_socket_deliver ( struct xfer_interface *socket,
+static int slam_socket_deliver ( struct slam_request *slam,
 				 struct io_buffer *iobuf,
 				 struct xfer_metadata *rx_meta __unused ) {
-	struct slam_request *slam =
-		container_of ( socket, struct slam_request, socket );
 	int rc;
 
 	/* Restart the master client timer */
@@ -597,90 +589,41 @@ static int slam_socket_deliver ( struct xfer_interface *socket,
 
 }
 
-/**
- * Close SLAM unicast socket
- *
- * @v socket		SLAM unicast socket
- * @v rc		Reason for close
- */
-static void slam_socket_close ( struct xfer_interface *socket, int rc ) {
-	struct slam_request *slam =
-		container_of ( socket, struct slam_request, socket );
-
-	DBGC ( slam, "SLAM %p unicast socket closed: %s\n",
-	       slam, strerror ( rc ) );
-
-	slam_finished ( slam, rc );
-}
-
-/** SLAM unicast socket data transfer operations */
-static struct xfer_interface_operations slam_socket_operations = {
-	.close		= slam_socket_close,
-	.vredirect	= xfer_vreopen,
-	.window		= unlimited_xfer_window,
-	.alloc_iob	= default_xfer_alloc_iob,
-	.deliver_iob	= slam_socket_deliver,
-	.deliver_raw	= xfer_deliver_as_iob,
+/** SLAM unicast socket interface operations */
+static struct interface_operation slam_socket_operations[] = {
+	INTF_OP ( xfer_deliver, struct slam_request *, slam_socket_deliver ),
+	INTF_OP ( intf_close, struct slam_request *, slam_finished ),
 };
 
-/**
- * Close SLAM multicast socket
- *
- * @v mc_socket		SLAM multicast socket
- * @v rc		Reason for close
- */
-static void slam_mc_socket_close ( struct xfer_interface *mc_socket, int rc ){
-	struct slam_request *slam =
-		container_of ( mc_socket, struct slam_request, mc_socket );
-
-	DBGC ( slam, "SLAM %p multicast socket closed: %s\n",
-	       slam, strerror ( rc ) );
-
-	slam_finished ( slam, rc );
-}
+/** SLAM unicast socket interface descriptor */
+static struct interface_descriptor slam_socket_desc =
+	INTF_DESC ( struct slam_request, socket, slam_socket_operations );
 
-/** SLAM multicast socket data transfer operations */
-static struct xfer_interface_operations slam_mc_socket_operations = {
-	.close		= slam_mc_socket_close,
-	.vredirect	= xfer_vreopen,
-	.window		= unlimited_xfer_window,
-	.alloc_iob	= default_xfer_alloc_iob,
-	.deliver_iob	= slam_mc_socket_deliver,
-	.deliver_raw	= xfer_deliver_as_iob,
+/** SLAM multicast socket interface operations */
+static struct interface_operation slam_mc_socket_operations[] = {
+	INTF_OP ( xfer_deliver, struct slam_request *, slam_mc_socket_deliver ),
+	INTF_OP ( intf_close, struct slam_request *, slam_finished ),
 };
 
+/** SLAM multicast socket interface descriptor */
+static struct interface_descriptor slam_mc_socket_desc =
+	INTF_DESC ( struct slam_request, mc_socket, slam_mc_socket_operations );
+
 /****************************************************************************
  *
  * Data transfer interface
  *
  */
 
-/**
- * Close SLAM data transfer interface
- *
- * @v xfer		SLAM data transfer interface
- * @v rc		Reason for close
- */
-static void slam_xfer_close ( struct xfer_interface *xfer, int rc ) {
-	struct slam_request *slam =
-		container_of ( xfer, struct slam_request, xfer );
-
-	DBGC ( slam, "SLAM %p data transfer interface closed: %s\n",
-	       slam, strerror ( rc ) );
-
-	slam_finished ( slam, rc );
-}
-
-/** SLAM data transfer operations */
-static struct xfer_interface_operations slam_xfer_operations = {
-	.close		= slam_xfer_close,
-	.vredirect	= ignore_xfer_vredirect,
-	.window		= unlimited_xfer_window,
-	.alloc_iob	= default_xfer_alloc_iob,
-	.deliver_iob	= xfer_deliver_as_raw,
-	.deliver_raw	= ignore_xfer_deliver_raw,
+/** SLAM data transfer interface operations */
+static struct interface_operation slam_xfer_operations[] = {
+	INTF_OP ( intf_close, struct slam_request *, slam_finished ),
 };
 
+/** SLAM data transfer interface descriptor */
+static struct interface_descriptor slam_xfer_desc =
+	INTF_DESC ( struct slam_request, xfer, slam_xfer_operations );
+
 /**
  * Parse SLAM URI multicast address
  *
@@ -729,7 +672,7 @@ static int slam_parse_multicast_address ( struct slam_request *slam,
  * @v uri		Uniform Resource Identifier
  * @ret rc		Return status code
  */
-static int slam_open ( struct xfer_interface *xfer, struct uri *uri ) {
+static int slam_open ( struct interface *xfer, struct uri *uri ) {
 	static const struct sockaddr_in default_multicast = {
 		.sin_family = AF_INET,
 		.sin_port = htons ( SLAM_DEFAULT_MULTICAST_PORT ),
@@ -749,10 +692,9 @@ static int slam_open ( struct xfer_interface *xfer, struct uri *uri ) {
 	if ( ! slam )
 		return -ENOMEM;
 	ref_init ( &slam->refcnt, slam_free );
-	xfer_init ( &slam->xfer, &slam_xfer_operations, &slam->refcnt );
-	xfer_init ( &slam->socket, &slam_socket_operations, &slam->refcnt );
-	xfer_init ( &slam->mc_socket, &slam_mc_socket_operations,
-		    &slam->refcnt );
+	intf_init ( &slam->xfer, &slam_xfer_desc, &slam->refcnt );
+	intf_init ( &slam->socket, &slam_socket_desc, &slam->refcnt );
+	intf_init ( &slam->mc_socket, &slam_mc_socket_desc, &slam->refcnt );
 	timer_init ( &slam->master_timer, slam_master_timer_expired );
 	timer_init ( &slam->slave_timer, slam_slave_timer_expired );
 	/* Fake an invalid cached header of { 0x00, ... } */
@@ -795,7 +737,7 @@ static int slam_open ( struct xfer_interface *xfer, struct uri *uri ) {
 	start_timer_fixed ( &slam->slave_timer, SLAM_SLAVE_TIMEOUT );
 
 	/* Attach to parent interface, mortalise self, and return */
-	xfer_plug_plug ( &slam->xfer, xfer );
+	intf_plug_plug ( &slam->xfer, xfer );
 	ref_put ( &slam->refcnt );
 	return 0;
 
diff --git a/src/net/udp/tftp.c b/src/net/udp/tftp.c
index 5e98f58cd..3bcd0a258 100644
--- a/src/net/udp/tftp.c
+++ b/src/net/udp/tftp.c
@@ -27,6 +27,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #include <errno.h>
 #include <assert.h>
 #include <ipxe/refcnt.h>
+#include <ipxe/iobuf.h>
 #include <ipxe/xfer.h>
 #include <ipxe/open.h>
 #include <ipxe/uri.h>
@@ -79,14 +80,14 @@ struct tftp_request {
 	/** Reference count */
 	struct refcnt refcnt;
 	/** Data transfer interface */
-	struct xfer_interface xfer;
+	struct interface xfer;
 
 	/** URI being fetched */
 	struct uri *uri;
 	/** Transport layer interface */
-	struct xfer_interface socket;
+	struct interface socket;
 	/** Multicast transport layer interface */
-	struct xfer_interface mc_socket;
+	struct interface mc_socket;
 
 	/** Data block size
 	 *
@@ -183,12 +184,9 @@ static void tftp_done ( struct tftp_request *tftp, int rc ) {
 	stop_timer ( &tftp->timer );
 
 	/* Close all data transfer interfaces */
-	xfer_nullify ( &tftp->socket );
-	xfer_close ( &tftp->socket, rc );
-	xfer_nullify ( &tftp->mc_socket );
-	xfer_close ( &tftp->mc_socket, rc );
-	xfer_nullify ( &tftp->xfer );
-	xfer_close ( &tftp->xfer, rc );
+	intf_shutdown ( &tftp->socket, rc );
+	intf_shutdown ( &tftp->mc_socket, rc );
+	intf_shutdown ( &tftp->xfer, rc );
 }
 
 /**
@@ -202,7 +200,7 @@ static int tftp_reopen ( struct tftp_request *tftp ) {
 	int rc;
 
 	/* Close socket */
-	xfer_close ( &tftp->socket, 0 );
+	intf_restart ( &tftp->socket, 0 );
 
 	/* Disable ACK sending. */
 	tftp->flags &= ~TFTP_FL_SEND_ACK;
@@ -236,7 +234,7 @@ static int tftp_reopen_mc ( struct tftp_request *tftp,
 	int rc;
 
 	/* Close multicast socket */
-	xfer_close ( &tftp->mc_socket, 0 );
+	intf_restart ( &tftp->mc_socket, 0 );
 
 	/* Open multicast socket.  We never send via this socket, so
 	 * use the local address as the peer address (since the peer
@@ -423,7 +421,7 @@ static int tftp_send_ack ( struct tftp_request *tftp ) {
 	ack->block = htons ( block );
 
 	/* ACK always goes to the peer recorded from the RRQ response */
-	return xfer_deliver_iob_meta ( &tftp->socket, iobuf, &meta );
+	return xfer_deliver ( &tftp->socket, iobuf, &meta );
 }
 
 /**
@@ -459,7 +457,7 @@ static int tftp_send_error ( struct tftp_request *tftp, int errcode,
 	strcpy ( err->errmsg, errmsg );
 
 	/* ERR always goes to the peer recorded from the RRQ response */
-	return xfer_deliver_iob_meta ( &tftp->socket, iobuf, &meta );
+	return xfer_deliver ( &tftp->socket, iobuf, &meta );
 }
 
 /**
@@ -525,7 +523,7 @@ static void tftp_timer_expired ( struct retry_timer *timer, int fail ) {
 				tftp->flags = TFTP_FL_RRQ_SIZES;
 
 				/* Close multicast socket */
-				xfer_close ( &tftp->mc_socket, 0 );
+				intf_restart ( &tftp->mc_socket, 0 );
 
 				/* Reset retry timer */
 				start_timer_nodelay ( &tftp->timer );
@@ -858,8 +856,8 @@ static int tftp_rx_data ( struct tftp_request *tftp,
 	memset ( &meta, 0, sizeof ( meta ) );
 	meta.whence = SEEK_SET;
 	meta.offset = offset;
-	if ( ( rc = xfer_deliver_iob_meta ( &tftp->xfer, iob_disown ( iobuf ),
-					    &meta ) ) != 0 ) {
+	if ( ( rc = xfer_deliver ( &tftp->xfer, iob_disown ( iobuf ),
+				   &meta ) ) != 0 ) {
 		DBGC ( tftp, "TFTP %p could not deliver data: %s\n",
 		       tftp, strerror ( rc ) );
 		goto done;
@@ -998,16 +996,14 @@ static int tftp_rx ( struct tftp_request *tftp,
 /**
  * Receive new data via socket
  *
- * @v socket		Transport layer interface
+ * @v tftp		TFTP connection
  * @v iobuf		I/O buffer
  * @v meta		Transfer metadata
  * @ret rc		Return status code
  */
-static int tftp_socket_deliver_iob ( struct xfer_interface *socket,
-				     struct io_buffer *iobuf,
-				     struct xfer_metadata *meta ) {
-	struct tftp_request *tftp =
-		container_of ( socket, struct tftp_request, socket );
+static int tftp_socket_deliver ( struct tftp_request *tftp,
+				 struct io_buffer *iobuf,
+				 struct xfer_metadata *meta ) {
 
 	/* Enable sending ACKs when we receive a unicast packet.  This
 	 * covers three cases:
@@ -1030,67 +1026,30 @@ static int tftp_socket_deliver_iob ( struct xfer_interface *socket,
 }
 
 /** TFTP socket operations */
-static struct xfer_interface_operations tftp_socket_operations = {
-	.close		= ignore_xfer_close,
-	.vredirect	= xfer_vreopen,
-	.window		= unlimited_xfer_window,
-	.alloc_iob	= default_xfer_alloc_iob,
-	.deliver_iob	= tftp_socket_deliver_iob,
-	.deliver_raw	= xfer_deliver_as_iob,
+static struct interface_operation tftp_socket_operations[] = {
+	INTF_OP ( xfer_deliver, struct tftp_request *, tftp_socket_deliver ),
 };
 
-/**
- * Receive new data via multicast socket
- *
- * @v mc_socket		Multicast transport layer interface
- * @v iobuf		I/O buffer
- * @v meta		Transfer metadata
- * @ret rc		Return status code
- */
-static int tftp_mc_socket_deliver_iob ( struct xfer_interface *mc_socket,
-					struct io_buffer *iobuf,
-					struct xfer_metadata *meta ) {
-	struct tftp_request *tftp =
-		container_of ( mc_socket, struct tftp_request, mc_socket );
-
-	return tftp_rx ( tftp, iobuf, meta );
-}
+/** TFTP socket interface descriptor */
+static struct interface_descriptor tftp_socket_desc =
+	INTF_DESC ( struct tftp_request, socket, tftp_socket_operations );
 
 /** TFTP multicast socket operations */
-static struct xfer_interface_operations tftp_mc_socket_operations = {
-	.close		= ignore_xfer_close,
-	.vredirect	= xfer_vreopen,
-	.window		= unlimited_xfer_window,
-	.alloc_iob	= default_xfer_alloc_iob,
-	.deliver_iob	= tftp_mc_socket_deliver_iob,
-	.deliver_raw	= xfer_deliver_as_iob,
+static struct interface_operation tftp_mc_socket_operations[] = {
+	INTF_OP ( xfer_deliver, struct tftp_request *, tftp_rx ),
 };
 
-/**
- * Close TFTP data transfer interface
- *
- * @v xfer		Data transfer interface
- * @v rc		Reason for close
- */
-static void tftp_xfer_close ( struct xfer_interface *xfer, int rc ) {
-	struct tftp_request *tftp =
-		container_of ( xfer, struct tftp_request, xfer );
-
-	DBGC ( tftp, "TFTP %p interface closed: %s\n",
-	       tftp, strerror ( rc ) );
-
-	tftp_done ( tftp, rc );
-}
+/** TFTP multicast socket interface descriptor */
+static struct interface_descriptor tftp_mc_socket_desc =
+	INTF_DESC ( struct tftp_request, mc_socket, tftp_mc_socket_operations );
 
 /**
  * Check flow control window
  *
- * @v xfer		Data transfer interface
+ * @v tftp		TFTP connection
  * @ret len		Length of window
  */
-static size_t tftp_xfer_window ( struct xfer_interface *xfer ) {
-	struct tftp_request *tftp =
-		container_of ( xfer, struct tftp_request, xfer );
+static size_t tftp_xfer_window ( struct tftp_request *tftp ) {
 
 	/* We abuse this data-xfer method to convey the blocksize to
 	 * the caller.  This really should be done using some kind of
@@ -1101,15 +1060,15 @@ static size_t tftp_xfer_window ( struct xfer_interface *xfer ) {
 }
 
 /** TFTP data transfer interface operations */
-static struct xfer_interface_operations tftp_xfer_operations = {
-	.close		= tftp_xfer_close,
-	.vredirect	= ignore_xfer_vredirect,
-	.window		= tftp_xfer_window,
-	.alloc_iob	= default_xfer_alloc_iob,
-	.deliver_iob	= xfer_deliver_as_raw,
-	.deliver_raw	= ignore_xfer_deliver_raw,
+static struct interface_operation tftp_xfer_operations[] = {
+	INTF_OP ( xfer_window, struct tftp_request *, tftp_xfer_window ),
+	INTF_OP ( intf_close, struct tftp_request *, tftp_done ),
 };
 
+/** TFTP data transfer interface descriptor */
+static struct interface_descriptor tftp_xfer_desc =
+	INTF_DESC ( struct tftp_request, xfer, tftp_xfer_operations );
+
 /**
  * Initiate TFTP/TFTM/MTFTP download
  *
@@ -1117,7 +1076,7 @@ static struct xfer_interface_operations tftp_xfer_operations = {
  * @v uri		Uniform Resource Identifier
  * @ret rc		Return status code
  */
-static int tftp_core_open ( struct xfer_interface *xfer, struct uri *uri,
+static int tftp_core_open ( struct interface *xfer, struct uri *uri,
 			    unsigned int default_port,
 			    struct sockaddr *multicast,
 			    unsigned int flags ) {
@@ -1135,10 +1094,9 @@ static int tftp_core_open ( struct xfer_interface *xfer, struct uri *uri,
 	if ( ! tftp )
 		return -ENOMEM;
 	ref_init ( &tftp->refcnt, tftp_free );
-	xfer_init ( &tftp->xfer, &tftp_xfer_operations, &tftp->refcnt );
-	xfer_init ( &tftp->socket, &tftp_socket_operations, &tftp->refcnt );
-	xfer_init ( &tftp->mc_socket, &tftp_mc_socket_operations,
-		    &tftp->refcnt );
+	intf_init ( &tftp->xfer, &tftp_xfer_desc, &tftp->refcnt );
+	intf_init ( &tftp->socket, &tftp_socket_desc, &tftp->refcnt );
+	intf_init ( &tftp->mc_socket, &tftp_mc_socket_desc, &tftp->refcnt );
 	timer_init ( &tftp->timer, tftp_timer_expired );
 	tftp->uri = uri_get ( uri );
 	tftp->blksize = TFTP_DEFAULT_BLKSIZE;
@@ -1159,7 +1117,7 @@ static int tftp_core_open ( struct xfer_interface *xfer, struct uri *uri,
 	start_timer_nodelay ( &tftp->timer );
 
 	/* Attach to parent interface, mortalise self, and return */
-	xfer_plug_plug ( &tftp->xfer, xfer );
+	intf_plug_plug ( &tftp->xfer, xfer );
 	ref_put ( &tftp->refcnt );
 	return 0;
 
@@ -1178,7 +1136,7 @@ static int tftp_core_open ( struct xfer_interface *xfer, struct uri *uri,
  * @v uri		Uniform Resource Identifier
  * @ret rc		Return status code
  */
-static int tftp_open ( struct xfer_interface *xfer, struct uri *uri ) {
+static int tftp_open ( struct interface *xfer, struct uri *uri ) {
 	return tftp_core_open ( xfer, uri, TFTP_PORT, NULL,
 				TFTP_FL_RRQ_SIZES );
 
@@ -1197,7 +1155,7 @@ struct uri_opener tftp_uri_opener __uri_opener = {
  * @v uri		Uniform Resource Identifier
  * @ret rc		Return status code
  */
-static int tftpsize_open ( struct xfer_interface *xfer, struct uri *uri ) {
+static int tftpsize_open ( struct interface *xfer, struct uri *uri ) {
 	return tftp_core_open ( xfer, uri, TFTP_PORT, NULL,
 				( TFTP_FL_RRQ_SIZES |
 				  TFTP_FL_SIZEONLY ) );
@@ -1217,7 +1175,7 @@ struct uri_opener tftpsize_uri_opener __uri_opener = {
  * @v uri		Uniform Resource Identifier
  * @ret rc		Return status code
  */
-static int tftm_open ( struct xfer_interface *xfer, struct uri *uri ) {
+static int tftm_open ( struct interface *xfer, struct uri *uri ) {
 	return tftp_core_open ( xfer, uri, TFTP_PORT, NULL,
 				( TFTP_FL_RRQ_SIZES |
 				  TFTP_FL_RRQ_MULTICAST ) );
@@ -1237,7 +1195,7 @@ struct uri_opener tftm_uri_opener __uri_opener = {
  * @v uri		Uniform Resource Identifier
  * @ret rc		Return status code
  */
-static int mtftp_open ( struct xfer_interface *xfer, struct uri *uri ) {
+static int mtftp_open ( struct interface *xfer, struct uri *uri ) {
 	return tftp_core_open ( xfer, uri, MTFTP_PORT,
 				( struct sockaddr * ) &tftp_mtftp_socket,
 				TFTP_FL_MTFTP_RECOVERY );