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qcow2: No persistent dirty bitmaps for compat=0.10

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Persistent dirty bitmaps require a properly functioning
autoclear_features field, or we cannot track when an unsupporting
program might overwrite them.  Therefore, we cannot support them for
compat=0.10 images.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-id: 20171123020832.8165-3-mreitz@redhat.com
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Max Reitz 2017-11-23 03:08:17 +01:00
parent 3c363575dc
commit c9ceb3ec8a
2 changed files with 21 additions and 3 deletions
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10
block/qcow2-bitmap.c
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@ -1449,6 +1449,16 @@ bool qcow2_can_store_new_dirty_bitmap(BlockDriverState *bs,
bool found;
Qcow2BitmapList *bm_list;
if (s->qcow_version < 3) {
/* Without autoclear_features, we would always have to assume
* that a program without persistent dirty bitmap support has
* accessed this qcow2 file when opening it, and would thus
* have to drop all dirty bitmaps (defeating their purpose).
*/
error_setg(errp, "Cannot store dirty bitmaps in qcow2 v2 files");
goto fail;
}
if (check_constraints_on_bitmap(bs, name, granularity, errp) != 0) {
goto fail;
}