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qcow2: Reuse preallocated zero clusters

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Instead of just freeing preallocated zero clusters and completely
allocating them from scratch, reuse them.

We cannot do this in handle_copied(), however, since this is a COW
operation. Therefore, we have to add the new logic to handle_alloc() and
simply return the existing offset if it exists. The only catch is that
we have to convince qcow2_alloc_cluster_link_l2() not to free the old
clusters (because we have reused them).

Reported-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Max Reitz 2017-05-04 01:11:18 +02:00 • committed by Kevin Wolf
parent 92413c16be
commit 564a6b6938
2 changed files with 61 additions and 26 deletions
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3
block/qcow2.h
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@ -322,6 +322,9 @@ typedef struct QCowL2Meta
/** Number of newly allocated clusters */
int nb_clusters;
/** Do not free the old clusters */
bool keep_old_clusters;
/**
* Requests that overlap with this allocation and wait to be restarted
* when the allocating request has completed.