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qemu-patch-raspberry4
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qcow2: Avoid COW during metadata preallocation 

Limiting the allocation to INT_MAX bytes isn't particularly clever
because it means that the final cluster will be a partial cluster which
will be completed through a COW operation. This results in unnecessary
data read and write requests which lead to an unwanted non-sparse
filesystem block for metadata preallocation.

Align the maximum allocation size down to the cluster size to avoid this
situation.

Cc: qemu-stable@nongnu.org
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
(cherry picked from commit f29fbf7c6b)
*modified to avoid functional dependency on 93e32b3e
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
stable-3.1
Kevin Wolf 2019-04-15 16:25:01 +02:00 committed by Michael Roth
parent b443db97c1
commit c627cc38be
1 changed files with 2 additions and 1 deletions
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3
block/qcow2.c
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@ -2590,6 +2590,7 @@ static int qcow2_set_up_encryption(BlockDriverState *bs,
static int coroutine_fn preallocate_co(BlockDriverState *bs, uint64_t offset,
uint64_t new_length)
{
BDRVQcow2State *s = bs->opaque;
uint64_t bytes;
uint64_t host_offset = 0;
unsigned int cur_bytes;
@ -2600,7 +2601,7 @@ static int coroutine_fn preallocate_co(BlockDriverState *bs, uint64_t offset,
bytes = new_length - offset;
while (bytes) {
cur_bytes = MIN(bytes, INT_MAX);
cur_bytes = MIN(bytes, QEMU_ALIGN_DOWN(INT_MAX, s->cluster_size));
ret = qcow2_alloc_cluster_offset(bs, offset, &cur_bytes,
&host_offset, &meta);
if (ret < 0) {