From 26d356fa2c253affac69543298accca6406045ca Mon Sep 17 00:00:00 2001
From: Simon Rettberg
Date: Thu, 12 Apr 2018 23:29:28 +0200
Subject: [SERVER] Add bgrMinClients: Thresold to control when BGR starts

Background replication will not kick in if there aren't at least
that many clients connected.
---
 conf/server.conf     | 2 ++
 src/server/globals.c | 7 +++++--
 src/server/globals.h | 5 +++++
 src/server/uplink.c  | 9 ++++++---
 4 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/conf/server.conf b/conf/server.conf
index a33a84e..2f43247 100644
--- a/conf/server.conf
+++ b/conf/server.conf
@@ -11,6 +11,8 @@ clientPenalty=0
 isProxy=true
 ; if proxy is true and an image is incomplete, should idle bandwidth be used to replicate missing blocks?
 backgroundReplication=true
+; minimum amount of connected clients for background replication to kick in
+bgrMinClients=0
 ; if isProxy==true and another proxy requests and image that we don't have, should we ask our alt-servers for it?
 lookupMissingForProxy=true
 ; create sparse files instead of preallocating; ignored if backgroundReplication=true -- only recommended if cache space is small
diff --git a/src/server/globals.c b/src/server/globals.c
index a59974f..932b3d5 100644
--- a/src/server/globals.c
+++ b/src/server/globals.c
@@ -17,6 +17,7 @@ int _serverPenalty = 0;
 int _clientPenalty = 0;
 bool _isProxy = false;
 bool _backgroundReplication = true;
+int _bgrMinClients = 0;
 bool _lookupMissingForProxy = true;
 bool _sparseFiles = false;
 bool _removeMissingImages = true;
@@ -55,6 +56,7 @@ static int ini_handler(void *custom UNUSED, const char* section, const char* key
 	SAVE_TO_VAR_BOOL( dnbd3, isProxy );
 	SAVE_TO_VAR_BOOL( dnbd3, proxyPrivateOnly );
 	SAVE_TO_VAR_BOOL( dnbd3, backgroundReplication );
+	SAVE_TO_VAR_INT( dnbd3, bgrMinClients );
 	SAVE_TO_VAR_BOOL( dnbd3, lookupMissingForProxy );
 	SAVE_TO_VAR_BOOL( dnbd3, sparseFiles );
 	SAVE_TO_VAR_BOOL( dnbd3, removeMissingImages );
@@ -150,8 +152,8 @@ void globals_loadConfig()
 			}
 		}
 	}
-	if ( _backgroundReplication && _sparseFiles ) {
-		logadd( LOG_WARNING, "Ignoring 'sparseFiles=true' since backgroundReplication is set to true" );
+	if ( _backgroundReplication && _sparseFiles && _bgrMinClients < 5 ) {
+		logadd( LOG_WARNING, "Ignoring 'sparseFiles=true' since backgroundReplication is set to true and bgrMinClients is too low" );
 		_sparseFiles = false;
 	}
 	// Dump config as interpreted
@@ -264,6 +266,7 @@ size_t globals_dumpConfig(char *buffer, size_t size)
 	PINT(clientPenalty);
 	PBOOL(isProxy);
 	PBOOL(backgroundReplication);
+	PINT(bgrMinClients);
 	PBOOL(lookupMissingForProxy);
 	PBOOL(sparseFiles);
 	PBOOL(removeMissingImages);
diff --git a/src/server/globals.h b/src/server/globals.h
index d43878f..2e39cb8 100644
--- a/src/server/globals.h
+++ b/src/server/globals.h
@@ -206,6 +206,11 @@ extern bool _closeUnusedFd;
  */
 extern bool _backgroundReplication;
 
+/**
+ * Minimum connected clients for background replication to kick in
+ */
+extern int _bgrMinClients;
+
 /**
  * (In proxy mode): If connecting client is a proxy, and the requested image
  * is not known locally, should we ask our known alt servers for it?
diff --git a/src/server/uplink.c b/src/server/uplink.c
index 2cf8b7d..debd091 100644
--- a/src/server/uplink.c
+++ b/src/server/uplink.c
@@ -375,7 +375,10 @@ static void* uplink_mainloop(void *data)
 		declare_now;
 		if ( link->fd != -1 && link->replicationHandle == 0 && timing_reached( &nextKeepalive, &now ) ) {
 			timing_set( &nextKeepalive, &now, 20 );
-			if ( !uplink_sendKeepalive( link->fd ) ) {
+			if ( uplink_sendKeepalive( link->fd ) ) {
+				// Re-trigger periodically, in case it requires a minimum user count
+				uplink_sendReplicationRequest( link );
+			} else {
 				const int fd = link->fd;
 				link->fd = -1;
 				close( fd );
@@ -514,8 +517,8 @@ static void uplink_sendReplicationRequest(dnbd3_connection_t *link)
 	dnbd3_image_t * const image = link->image;
 	if ( image->realFilesize < DNBD3_BLOCK_SIZE ) return;
 	spin_lock( &image->lock );
-	if ( image == NULL || image->cache_map == NULL || link->replicationHandle != 0 ) {
-		// No cache map (=image complete), or replication pending, do nothing
+	if ( image == NULL || image->cache_map == NULL || link->replicationHandle != 0 || image->users < _bgrMinClients ) {
+		// No cache map (=image complete), or replication pending, or not enough users, do nothing
 		spin_unlock( &image->lock );
 		return;
 	}
-- 
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