* [PULL 0/1] Block patch
@ 2021-06-24 11:43 Max Reitz
2021-06-24 11:43 ` [PULL 1/1] block/snapshot: Clarify goto fallback behavior Max Reitz
2021-06-25 16:04 ` [PULL 0/1] Block patch Peter Maydell
0 siblings, 2 replies; 3+ messages in thread
From: Max Reitz @ 2021-06-24 11:43 UTC (permalink / raw)
To: qemu-block; +Cc: Kevin Wolf, Peter Maydell, qemu-devel, Max Reitz
The following changes since commit b22726abdfa54592d6ad88f65b0297c0e8b363e2:
Merge remote-tracking branch 'remotes/vivier2/tags/linux-user-for-6.1-pull-request' into staging (2021-06-22 16:07:53 +0100)
are available in the Git repository at:
https://github.com/XanClic/qemu.git tags/pull-block-2021-06-24
for you to fetch changes up to 32a9a245d719a883eef2cbf07d2cf89efa0206d0:
block/snapshot: Clarify goto fallback behavior (2021-06-24 09:49:04 +0200)
----------------------------------------------------------------
Block patch:
- Fix Coverity complaint in block/snapshot.c
----------------------------------------------------------------
Max Reitz (1):
block/snapshot: Clarify goto fallback behavior
block/snapshot.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
--
2.31.1
^ permalink raw reply [flat|nested] 3+ messages in thread
* [PULL 1/1] block/snapshot: Clarify goto fallback behavior
2021-06-24 11:43 [PULL 0/1] Block patch Max Reitz
@ 2021-06-24 11:43 ` Max Reitz
2021-06-25 16:04 ` [PULL 0/1] Block patch Peter Maydell
1 sibling, 0 replies; 3+ messages in thread
From: Max Reitz @ 2021-06-24 11:43 UTC (permalink / raw)
To: qemu-block; +Cc: Kevin Wolf, Peter Maydell, qemu-devel, Max Reitz
In the bdrv_snapshot_goto() fallback code, we work with a pointer to
either bs->file or bs->backing. We detach that child, close the node
(with .bdrv_close()), apply the snapshot on the child node, and then
re-open the node (with .bdrv_open()).
In order for .bdrv_open() to attach the same child node that we had
before, we pass "file={child-node}" or "backing={child-node}" to it.
Therefore, when .bdrv_open() has returned success, we can assume that
bs->file or bs->backing (respectively) points to our original child
again. This is verified by an assertion.
All of this is not immediately clear from a quick glance at the code,
so add a comment to the assertion what it is for, and why it is valid.
It certainly confused Coverity.
Reported-by: Coverity (CID 1452774)
Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20210503095418.31521-1-mreitz@redhat.com>
[mreitz: s/close/detach/]
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
block/snapshot.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/block/snapshot.c b/block/snapshot.c
index 6702c75e42..ccacda8bd5 100644
--- a/block/snapshot.c
+++ b/block/snapshot.c
@@ -275,13 +275,16 @@ int bdrv_snapshot_goto(BlockDriverState *bs,
qobject_unref(file_options);
g_free(subqdict_prefix);
+ /* Force .bdrv_open() below to re-attach fallback_bs on *fallback_ptr */
qdict_put_str(options, (*fallback_ptr)->name,
bdrv_get_node_name(fallback_bs));
+ /* Now close bs, apply the snapshot on fallback_bs, and re-open bs */
if (drv->bdrv_close) {
drv->bdrv_close(bs);
}
+ /* .bdrv_open() will re-attach it */
bdrv_unref_child(bs, *fallback_ptr);
*fallback_ptr = NULL;
@@ -296,7 +299,16 @@ int bdrv_snapshot_goto(BlockDriverState *bs,
return ret < 0 ? ret : open_ret;
}
- assert(fallback_bs == (*fallback_ptr)->bs);
+ /*
+ * fallback_ptr is &bs->file or &bs->backing. *fallback_ptr
+ * was closed above and set to NULL, but the .bdrv_open() call
+ * has opened it again, because we set the respective option
+ * (with the qdict_put_str() call above).
+ * 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);
bdrv_unref(fallback_bs);
return ret;
}
--
2.31.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PULL 0/1] Block patch
2021-06-24 11:43 [PULL 0/1] Block patch Max Reitz
2021-06-24 11:43 ` [PULL 1/1] block/snapshot: Clarify goto fallback behavior Max Reitz
@ 2021-06-25 16:04 ` Peter Maydell
1 sibling, 0 replies; 3+ messages in thread
From: Peter Maydell @ 2021-06-25 16:04 UTC (permalink / raw)
To: Max Reitz; +Cc: Kevin Wolf, QEMU Developers, Qemu-block
On Thu, 24 Jun 2021 at 12:43, Max Reitz <mreitz@redhat.com> wrote:
>
> The following changes since commit b22726abdfa54592d6ad88f65b0297c0e8b363e2:
>
> Merge remote-tracking branch 'remotes/vivier2/tags/linux-user-for-6.1-pull-request' into staging (2021-06-22 16:07:53 +0100)
>
> are available in the Git repository at:
>
> https://github.com/XanClic/qemu.git tags/pull-block-2021-06-24
>
> for you to fetch changes up to 32a9a245d719a883eef2cbf07d2cf89efa0206d0:
>
> block/snapshot: Clarify goto fallback behavior (2021-06-24 09:49:04 +0200)
>
> ----------------------------------------------------------------
> Block patch:
> - Fix Coverity complaint in block/snapshot.c
Applied, thanks.
Please update the changelog at https://wiki.qemu.org/ChangeLog/6.1
for any user-visible changes.
-- PMM
^ permalink raw reply [flat|nested] 3+ messages in thread
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