[SERVER] Make prefetching synchronous

There is a race condition where we process the next request from the
same client faster than the OS will schedule the async prefetch job,
rendering it a NOOP in the best case (request ranges match) or fetching
redundant data from the upstream server (prefetch range is larger than
actual request by client). Make prefetching synchronous to prevent this
race condition.

1 files changed, 16 insertions, 13 deletions

diff --git a/src/server/globals.c b/src/server/globals.c
index f689705..8ef7aec 100644
--- a/src/server/globals.c
+++ b/src/server/globals.c
@@ -24,19 +24,20 @@ atomic_bool _lookupMissingForProxy = true;
 atomic_bool _sparseFiles = false;
 atomic_bool _ignoreAllocErrors = false;
 atomic_bool _removeMissingImages = true;
-atomic_int _uplinkTimeout = SOCKET_TIMEOUT_UPLINK;
-atomic_int _clientTimeout = SOCKET_TIMEOUT_CLIENT;
+atomic_uint _uplinkTimeout = SOCKET_TIMEOUT_UPLINK;
+atomic_uint _clientTimeout = SOCKET_TIMEOUT_CLIENT;
 atomic_bool _closeUnusedFd = false;
 atomic_bool _vmdkLegacyMode = false;
 // Not really needed anymore since we have '+' and '-' in alt-servers
 atomic_bool _proxyPrivateOnly = false;
+atomic_bool _pretendClient = false;
 atomic_int _autoFreeDiskSpaceDelay = 3600 * 10;
 // [limits]
 atomic_int _maxClients = SERVER_MAX_CLIENTS;
 atomic_int _maxImages = SERVER_MAX_IMAGES;
-atomic_int _maxPayload = 9000000; // 9MB
+atomic_uint _maxPayload = 9000000; // 9MB
 atomic_uint_fast64_t _maxReplicationSize = (uint64_t)100000000000LL;
-atomic_bool _pretendClient = false;
+atomic_uint _maxPrefetch = 262144; // 256KB
 
 /**
  * True when loading config the first time. Consecutive loads will
@@ -60,17 +61,17 @@ static const char* units = "KMGTPEZY";
 
 static bool parse64(const char *in, atomic_int_fast64_t *out, const char *optname);
 static bool parse64u(const char *in, atomic_uint_fast64_t *out, const char *optname);
-static bool parse32(const char *in, atomic_int *out, const char *optname) UNUSED;
-static bool parse32u(const char *in, atomic_int *out, const char *optname);
+static bool parse32(const char *in, atomic_int *out, const char *optname);
+static bool parse32u(const char *in, atomic_uint *out, const char *optname);
 
 static int ini_handler(void *custom UNUSED, const char* section, const char* key, const char* value)
 {
 	if ( initialLoad ) {
 		if ( _basePath == NULL ) SAVE_TO_VAR_STR( dnbd3, basePath );
 		SAVE_TO_VAR_BOOL( dnbd3, vmdkLegacyMode );
-		SAVE_TO_VAR_UINT( dnbd3, listenPort );
-		SAVE_TO_VAR_UINT( limits, maxClients );
-		SAVE_TO_VAR_UINT( limits, maxImages );
+		SAVE_TO_VAR_INT( dnbd3, listenPort );
+		SAVE_TO_VAR_INT( limits, maxClients );
+		SAVE_TO_VAR_INT( limits, maxImages );
 	}
 	SAVE_TO_VAR_BOOL( dnbd3, isProxy );
 	SAVE_TO_VAR_BOOL( dnbd3, proxyPrivateOnly );
@@ -81,12 +82,13 @@ static int ini_handler(void *custom UNUSED, const char* section, const char* key
 	SAVE_TO_VAR_BOOL( dnbd3, ignoreAllocErrors );
 	SAVE_TO_VAR_BOOL( dnbd3, removeMissingImages );
 	SAVE_TO_VAR_BOOL( dnbd3, closeUnusedFd );
-	SAVE_TO_VAR_UINT( dnbd3, serverPenalty );
-	SAVE_TO_VAR_UINT( dnbd3, clientPenalty );
+	SAVE_TO_VAR_INT( dnbd3, serverPenalty );
+	SAVE_TO_VAR_INT( dnbd3, clientPenalty );
 	SAVE_TO_VAR_UINT( dnbd3, uplinkTimeout );
 	SAVE_TO_VAR_UINT( dnbd3, clientTimeout );
 	SAVE_TO_VAR_UINT( limits, maxPayload );
 	SAVE_TO_VAR_UINT64( limits, maxReplicationSize );
+	SAVE_TO_VAR_UINT( limits, maxPrefetch );
 	SAVE_TO_VAR_BOOL( dnbd3, pretendClient );
 	SAVE_TO_VAR_INT( dnbd3, autoFreeDiskSpaceDelay );
 	if ( strcmp( section, "dnbd3" ) == 0 && strcmp( key, "backgroundReplication" ) == 0 ) {
@@ -295,7 +297,7 @@ static bool parse32(const char *in, atomic_int *out, const char *optname)
 	return true;
 }
 
-static bool parse32u(const char *in, atomic_int *out, const char *optname)
+static bool parse32u(const char *in, atomic_uint *out, const char *optname)
 {
 	atomic_int_fast64_t v;
 	if ( !parse64( in, &v, optname ) ) return false;
@@ -303,7 +305,7 @@ static bool parse32u(const char *in, atomic_int *out, const char *optname)
 		logadd( LOG_WARNING, "'%s' must be between %d and %d, but is '%s'", optname, (int)0, (int)INT_MAX, in );
 		return false;
 	}
-	*out = (int)v;
+	*out = (unsigned int)v;
 	return true;
 }
 
@@ -351,6 +353,7 @@ size_t globals_dumpConfig(char *buffer, size_t size)
 	PINT(maxImages);
 	PINT(maxPayload);
 	PUINT64(maxReplicationSize);
+	PINT(maxPrefetch);
 	return size - rem;
 }