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qcow2: Don't strand clusters near 2G intervals during commit

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The qcow2_make_empty() function is reached during 'qemu-img commit',
in order to clear out ALL clusters of an image.  However, if the
image cannot use the fast code path (true if the image is format
0.10, or if the image contains a snapshot), the cluster size is
larger than 512, and the image is larger than 2G in size, then our
choice of sector_step causes problems.  Since it is not cluster
aligned, but qcow2_discard_clusters() silently ignores an unaligned
head or tail, we are leaving clusters allocated.

Enhance the testsuite to expose the flaw, and patch the problem by
ensuring our step size is aligned.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Eric Blake 2016-12-05 09:49:34 -06:00 • committed by Kevin Wolf
parent bc66cedb41
commit a3e1505dae
3 changed files with 210 additions and 83 deletions
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3
block/qcow2.c
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@ -2808,7 +2808,8 @@ static int qcow2_make_empty(BlockDriverState *bs)
{
BDRVQcow2State *s = bs->opaque;
uint64_t start_sector;
int sector_step = INT_MAX / BDRV_SECTOR_SIZE;
int sector_step = (QEMU_ALIGN_DOWN(INT_MAX, s->cluster_size) /
BDRV_SECTOR_SIZE);
int l1_clusters, ret = 0;
l1_clusters = DIV_ROUND_UP(s->l1_size, s->cluster_size / sizeof(uint64_t));