From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1LDMUL-0007Ds-8q for qemu-devel@nongnu.org; Thu, 18 Dec 2008 12:16:41 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1LDMUK-0007DY-NO for qemu-devel@nongnu.org; Thu, 18 Dec 2008 12:16:40 -0500 Received: from [199.232.76.173] (port=47772 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1LDMUK-0007DP-CA for qemu-devel@nongnu.org; Thu, 18 Dec 2008 12:16:40 -0500 Received: from ns.suse.de ([195.135.220.2]:39384 helo=mx1.suse.de) by monty-python.gnu.org with esmtps (TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1LDMUJ-00021o-ST for qemu-devel@nongnu.org; Thu, 18 Dec 2008 12:16:40 -0500 Message-ID: <494A8690.1080309@suse.de> Date: Thu, 18 Dec 2008 18:21:20 +0100 From: Kevin Wolf MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="------------010908060809040606070702" Subject: [Qemu-devel] [PATCH] qcow2: Fix cluster allocation Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: qemu-devel@nongnu.org, Gleb Natapov This is a multi-part message in MIME format. --------------010908060809040606070702 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit When allocating multiple clusters at once, the qcow2 implementation tries to find as many physically contiguous clusters as possible to allow larger writes. This search includes allocated clusters which are in the right place and still free clusters. If the range to allocate spans clusters in patterns like "10 allocated, then 10 free, then again 10 allocated" it is only checked that the chunks of allocated clusters are contiguous for themselves. However, what is actually needed is to have _all_ allocated clusters contiguous, starting at the first cluster of the allocation and spanning multiple such chunks. This patch changes the check so that each offset is not compared to the offset of the first cluster in its own chunk but to the first cluster in the whole allocation. I haven't seen it happen, but without this fix data corruption on qcow2 images is possible. This patch is meant to be applied on top of Gleb's compressed image fix. Signed-off-by: Kevin Wolf --------------010908060809040606070702 Content-Type: text/x-patch; name="qcow2-fix-contiguous-alloc.patch" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="qcow2-fix-contiguous-alloc.patch" Index: qemu-svn/block-qcow2.c =================================================================== --- qemu-svn.orig/block-qcow2.c +++ qemu-svn/block-qcow2.c @@ -615,7 +615,7 @@ static int size_to_clusters(BDRVQcowStat } static int count_contiguous_clusters(uint64_t nb_clusters, int cluster_size, - uint64_t *l2_table, uint64_t mask) + uint64_t *l2_table, uint64_t start, uint64_t mask) { int i; uint64_t offset = be64_to_cpu(l2_table[0]) & ~mask; @@ -623,11 +623,11 @@ static int count_contiguous_clusters(uin if (!offset) return 0; - for (i = 0; i < nb_clusters; i++) + for (i = start; i < start + nb_clusters; i++) if (offset + i * cluster_size != (be64_to_cpu(l2_table[i]) & ~mask)) break; - return i; + return (i - start); } static int count_contiguous_free_clusters(uint64_t nb_clusters, uint64_t *l2_table) @@ -714,7 +714,7 @@ static uint64_t get_cluster_offset(Block } else { /* how many allocated clusters ? */ c = count_contiguous_clusters(nb_clusters, s->cluster_size, - &l2_table[l2_index], QCOW_OFLAG_COPIED); + &l2_table[l2_index], 0, QCOW_OFLAG_COPIED); } nb_available = (c * s->cluster_sectors); @@ -968,7 +968,7 @@ static uint64_t alloc_cluster_offset(Blo if (cluster_offset & QCOW_OFLAG_COPIED) { nb_clusters = count_contiguous_clusters(nb_clusters, s->cluster_size, - &l2_table[l2_index], 0); + &l2_table[l2_index], 0, 0); cluster_offset &= ~QCOW_OFLAG_COPIED; m->nb_clusters = 0; @@ -985,7 +985,7 @@ static uint64_t alloc_cluster_offset(Blo while (i < nb_clusters) { i += count_contiguous_clusters(nb_clusters - i, s->cluster_size, - &l2_table[l2_index + i], 0); + &l2_table[l2_index], i, 0); if(be64_to_cpu(l2_table[l2_index + i])) break; --------------010908060809040606070702--