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qcow2: Implement bdrv_make_empty()

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Implement this function by making all clusters in the image file fall
through to the backing file (by using the recently extended discard).

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-id: 1414159063-25977-3-git-send-email-mreitz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Max Reitz 2014-10-24 15:57:31 +02:00 committed by Stefan Hajnoczi
parent 808c4b6f30
commit 491d27e2af
1 changed files with 27 additions and 0 deletions
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27
block/qcow2.c
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@ -2230,6 +2230,32 @@ fail:
return ret;
}
static int qcow2_make_empty(BlockDriverState *bs)
{
int ret = 0;
uint64_t start_sector;
int sector_step = INT_MAX / BDRV_SECTOR_SIZE;
for (start_sector = 0; start_sector < bs->total_sectors;
start_sector += sector_step)
{
/* As this function is generally used after committing an external
* snapshot, QCOW2_DISCARD_SNAPSHOT seems appropriate. Also, the
* default action for this kind of discard is to pass the discard,
* which will ideally result in an actually smaller image file, as
* is probably desired. */
ret = qcow2_discard_clusters(bs, start_sector * BDRV_SECTOR_SIZE,
MIN(sector_step,
bs->total_sectors - start_sector),
QCOW2_DISCARD_SNAPSHOT, true);
if (ret < 0) {
break;
}
}
return ret;
}
static coroutine_fn int qcow2_co_flush_to_os(BlockDriverState *bs)
{
BDRVQcowState *s = bs->opaque;
@ -2676,6 +2702,7 @@ static BlockDriver bdrv_qcow2 = {
.bdrv_co_discard = qcow2_co_discard,
.bdrv_truncate = qcow2_truncate,
.bdrv_write_compressed = qcow2_write_compressed,
.bdrv_make_empty = qcow2_make_empty,
.bdrv_snapshot_create = qcow2_snapshot_create,
.bdrv_snapshot_goto = qcow2_snapshot_goto,