Re: [Qemu-devel] [PATCH v3 10/13] block: Simplify bdrv_append_temp_snapshot() logic

[Kevin Wolf <kwolf@redhat.com>]

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Am 06.04.2017 um 14:52 hat Eric Blake geschrieben:
> On 04/06/2017 04:00 AM, Kevin Wolf wrote:
> > Am 05.04.2017 um 21:47 hat Eric Blake geschrieben:
> >> Noticed while checking Coccinelle results. Naming a label 'out:'
> >> when it is only used on error paths is weird; meanwhile we know
> >> that snapshot_options is NULL on success and that QDECREF(NULL)
> >> is safe.  So merge the two exit paths into one.
> >>
> >> Signed-off-by: Eric Blake <eblake@redhat.com>
> >> ---
> >>  block.c | 7 ++-----
> >>  1 file changed, 2 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/block.c b/block.c
> >> index 9b87bf6..a13625f 100644
> >> --- a/block.c
> >> +++ b/block.c
> >> @@ -2209,13 +2209,10 @@ static BlockDriverState *bdrv_append_temp_snapshot(BlockDriverState *bs,
> >>          goto out;
> >>      }
> >>
> >> +out:
> >> +    QDECREF(snapshot_options);
> >>      g_free(tmp_filename);
> >>      return bs_snapshot;
> > 
> > bs_snapshot is uninitialised or at least the wrong return value in error
> > cases. (Hm... Shouldn't the compiler catch the uninitialised part?)
> 
> Odd, and I agree that I recall the compiler generally able to catch that
> (maybe it's a matter of compiling with -g vs. -O2).  I'm surprised the
> autobuilder didn't flag it.  (I think I missed it due to rebase churn on
> my end).  The obvious fix is to:
> 
> -    BlockDriverState *bs_snapshot;
> +    BlockDriverState *bs_snapshot = NULL;

That's just half of the fix. It doesn't fix the cases where bs_snapshot
is already set. We still want to return NULL on errors there.

Kevin

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