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block/snapshot: stress that we fallback to primary child 

Actually what we chose is a primary child. Let's stress it in the code.

We are going to drop indirect pointer logic here in future. Actually
this commit simplifies the future work: we drop use of indirection in
the assertion now.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220726201134.924743-9-vsementsov@yandex-team.ru>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Vladimir Sementsov-Ogievskiy 2022-07-26 23:11:27 +03:00 committed by Kevin Wolf
parent 71ca43852a
commit 0c6100a7ff
1 changed files with 10 additions and 20 deletions
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30
block/snapshot.c
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@ -161,21 +161,14 @@ bool bdrv_snapshot_find_by_id_and_name(BlockDriverState *bs,
static BdrvChild **bdrv_snapshot_fallback_ptr(BlockDriverState *bs) static BdrvChild **bdrv_snapshot_fallback_ptr(BlockDriverState *bs)
{ {
BdrvChild **fallback; BdrvChild **fallback;
BdrvChild *child; BdrvChild *child = bdrv_primary_child(bs);
/* /* We allow fallback only to primary child */
* The only BdrvChild pointers that are safe to modify (and which if (!child) {
* we can thus return a reference to) are bs->file and
* bs->backing.
*/
fallback = &bs->file;
if (!*fallback && bs->drv && bs->drv->is_filter) {
fallback = &bs->backing;
}
if (!*fallback) {
return NULL; return NULL;
} }
fallback = (child == bs->file ? &bs->file : &bs->backing);
assert(*fallback == child);
/* /*
* Check that there are no other children that would need to be * Check that there are no other children that would need to be
@ -309,15 +302,12 @@ int bdrv_snapshot_goto(BlockDriverState *bs,
} }
/* /*
* fallback_ptr is &bs->file or &bs->backing. *fallback_ptr * fallback was a primary child. It was closed above and set to NULL,
* was closed above and set to NULL, but the .bdrv_open() call * but the .bdrv_open() call has opened it again, because we set the
* has opened it again, because we set the respective option * respective option (with the qdict_put_str() call above).
* (with the qdict_put_str() call above). * Assert that .bdrv_open() has attached the right BDS as primary child.
* Assert that .bdrv_open() has attached some child on
* *fallback_ptr, and that it has attached the one we wanted
* it to (i.e., fallback_bs).
*/ */
assert(*fallback_ptr && fallback_bs == (*fallback_ptr)->bs); assert(bdrv_primary_bs(bs) == fallback_bs);
bdrv_unref(fallback_bs); bdrv_unref(fallback_bs);
return ret; return ret;
} }