Re: [Xen-devel] [PATCH RESEND] libxl: Avoid realloc(, 0) when libxl__xs_directory returns empty list

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Ian Campbell writes ("Re: [PATCH RESEND] libxl: Avoid realloc(,0) when 
libxl__xs_directory returns empty list"):
> On Tue, 2013-11-12 at 17:23 +0000, Ian Jackson wrote:
> > Ping.
> 
> I could have sworn this went in...

Yes.  I have found a bunch of these lying around in branches in my
main tree.

> > In three places in libxl this may result in a zero size argument being
> > passed to malloc() or realloc(), which is not adviseable.
> 
> I thought it was strictly speaking fine, but I can see why it would be
> best to avoid.

Calling malloc(0) merely produces a fiddly-to-deal-with corner case,
where it may succeed by returning 0.

realloc(something,0) is actually wrong.  If it returns 0 you don't
know whether that means "I tried to allocate you a new 0-length block,
but failed, so your original block is still there" or "I have
successfully freed your old block; have this null pointer as an
answer".

> > Signed-off-by: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
> > Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> 
> Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

Committed-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>

And put on the backport list.

Thanks,
Ian.

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