[SERVER] Experimental support for sparse files in proxy mode

Will not preallocate images in this mode. Old images are only
deleted if the disk is full, determined by write() calls to
the cache file yielding ENOSPC or EDQUOT. In such a case,
the least recently used image(s) will be deleted to free
up at least 256MiB, and then the write() call will be repeated.
This *should* work somewhat reliably unless the cache partition
is ridiculously small. Performance might suffer a little, and
disk fragmentation might occur much faster than in prealloc
mode. Testing is needed.

1 files changed, 10 insertions, 1 deletions

diff --git a/src/server/uplink.c b/src/server/uplink.c
index aec47cb..b166c6d 100644
--- a/src/server/uplink.c
+++ b/src/server/uplink.c
@@ -592,10 +592,19 @@ static void uplink_handleReceive(dnbd3_connection_t *link)
 		spin_unlock( &link->image->lock );
 		// 1) Write to cache file
 		if ( link->image->cacheFd != -1 ) {
+			bool tryFree = true;
 			uint32_t done = 0;
 			while ( done < inReply.size ) {
 				ret = (int)pwrite( link->image->cacheFd, link->recvBuffer + done, inReply.size - done, start + done );
-				if ( ret == -1 && errno == EINTR ) continue;
+				if ( ret == -1 ) {
+					if ( errno == EINTR ) continue;
+					if ( errno == ENOSPC || errno == EDQUOT ) {
+						// try to free 256MiB
+						if ( !tryFree || !image_ensureDiskSpaceLocked( 256ull * 1024 * 1024, true ) ) break;
+						tryFree = false;
+						continue; // Success, retry write
+					}
+				}
 				if ( ret <= 0 ) break;
 				done += (uint32_t)ret;
 			}