Re: 'fbno' possibly used uninitialized in xfs_alloc_ag_vextent_small()

Re: 'fbno' possibly used uninitialized in xfs_alloc_ag_vextent_small()

[Jesper Juhl]

On 17/08/06, Nathan Scott <nathans@sgi.com> wrote:
> Hi Jesper,
>
> On Wed, Aug 16, 2006 at 11:27:34PM +0200, Jesper Juhl wrote:
> > (Please keep me on Cc since I'm not subscribed to the XFS lists)
> >
> > The coverity checker found what looks to me like a valid case of
> > potentially uninitialized variable use (see below).
>
> It looks invalid, but its not, once again.  To understand why this
> isn't a problem requires looking at the xfs_alloc_ag_vextent_small
> call sites (there's only two).  If (*flen==0) is passed back out,
> then the value in *fbno is discarded, always.
>
> > So basically, if we hit the 'else' branch, then 'fbno' has not been
> > initialized and line 1490 will then use that uninitialized variable.
> >
> > What would prevent that from happening at some time??
>
> Nothing.  But its not a problem in practice.  However, that final
> else branch is very much unlikely, so theres no real cost to just
> initialising the local fbno to NULLAGBLOCK in that branch, and we
> future proof ourselves a bit that way I guess (in case the callers
> ever change - pretty unlikely, but we may as well).  How does the
> patch below look to you?
>
Looks good to me.

-- 
Jesper Juhl <jesper.juhl@gmail.com>
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