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block: Fix crash when loading snapshot on inactive node

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bdrv_is_read_only() only checks if the node is configured to be
read-only eventually, but even if it returns false, writing to the node
may not be permitted at the moment (because it's inactive).

bdrv_is_writable() checks that the node can be written to right now, and
this is what the snapshot operations really need.

Change bdrv_can_snapshot() to use bdrv_is_writable() to fix crashes like
the following:

$ ./qemu-system-x86_64 -hda /tmp/test.qcow2 -loadvm foo -incoming defer
qemu-system-x86_64: ../block/io.c:1990: int bdrv_co_write_req_prepare(BdrvChild *, int64_t, int64_t, BdrvTrackedRequest *, int): Assertion `!(bs->open_flags & BDRV_O_INACTIVE)' failed.

The resulting error message after this patch isn't perfect yet, but at
least it doesn't crash any more:

$ ./qemu-system-x86_64 -hda /tmp/test.qcow2 -loadvm foo -incoming defer
qemu-system-x86_64: Device 'ide0-hd0' is writable but does not support snapshots

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20231201142520.32255-2-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit d3007d348a)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
This commit is contained in:
Kevin Wolf 2023-12-01 15:25:18 +01:00 committed by Michael Tokarev
parent 71090deb4c
commit a629fee99b
1 changed files with 3 additions and 1 deletions
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4
block/snapshot.c
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@ -190,8 +190,10 @@ static BlockDriverState *bdrv_snapshot_fallback(BlockDriverState *bs)
int bdrv_can_snapshot(BlockDriverState *bs)
{
BlockDriver *drv = bs->drv;
GLOBAL_STATE_CODE();
if (!drv || !bdrv_is_inserted(bs) || bdrv_is_read_only(bs)) {
if (!drv || !bdrv_is_inserted(bs) || !bdrv_is_writable(bs)) {
return 0;
}