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qcow2: Optimize bdrv_make_empty()

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bdrv_make_empty() is currently only called if the current image
represents an external snapshot that has been committed to its base
image; it is therefore unlikely to have internal snapshots. In this
case, bdrv_make_empty() can be greatly sped up by emptying the L1 and
refcount table (while having the dirty flag set, which only works for
compat=1.1) and creating a trivial refcount structure.

If there are snapshots or for compat=0.10, fall back to the simple
implementation (discard all clusters).

[Applied s/clusters/cluster/ typo fix suggested by Eric Blake
--Stefan]

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 1414159063-25977-4-git-send-email-mreitz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Max Reitz 2014-10-24 15:57:32 +02:00 • committed by Stefan Hajnoczi
parent 491d27e2af
commit 94054183da
3 changed files with 168 additions and 1 deletions
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2
block/blkdebug.c
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@ -195,6 +195,8 @@ static const char *event_names[BLKDBG_EVENT_MAX] = {
[BLKDBG_PWRITEV] = "pwritev",
[BLKDBG_PWRITEV_ZERO] = "pwritev_zero",
[BLKDBG_PWRITEV_DONE] = "pwritev_done",
[BLKDBG_EMPTY_IMAGE_PREPARE] = "empty_image_prepare",
};
static int get_event_by_name(const char *name, BlkDebugEvent *event)