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Re: [PATCH v2] libxc: avoid clobbering errno in xc_domain_pod_target()
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>
- Date: Fri, 10 Dec 2021 13:50:47 +0000
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Anthony Perard <anthony.perard@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>
- Delivery-date: Fri, 10 Dec 2021 13:51:17 +0000
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- Thread-topic: [PATCH v2] libxc: avoid clobbering errno in xc_domain_pod_target()
Hi Jan
> On 10 Dec 2021, at 13:11, Jan Beulich <jbeulich@xxxxxxxx> wrote:
>
> do_memory_op() supplies return value and has "errno" set the usual way.
> Don't overwrite "errno" with 1 (aka EPERM on at least Linux). There's
> also no reason to overwrite "err".
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
But if err can really only be 0 or -1, I do wonder if the else forcing err to 0
could
be removed but I must say I have no idea if do_memory_op could return a value
>0.
Anyway not related to the patch itself.
Cheers
Bertrand
> ---
> While the hypervisor side of the hypercall gives the impression of being
> able to return positive values as of 637a283f17eb ("PoD: Allow
> pod_set_cache_target hypercall to be preempted"), due to the use of
> "rc >= 0" there, afaict that's not actually the case. IOW "err" can
> really only be 0 or -1 here, and hence its setting to zero may also be
> worthwhile to drop.
> ---
> v2: Don't save/restore errno, as DPRINTF() already does so.
>
> --- a/tools/libs/ctrl/xc_domain.c
> +++ b/tools/libs/ctrl/xc_domain.c
> @@ -1230,13 +1230,9 @@ static int xc_domain_pod_target(xc_inter
> err = do_memory_op(xch, op, &pod_target, sizeof(pod_target));
>
> if ( err < 0 )
> - {
> DPRINTF("Failed %s_pod_target dom %d\n",
> (op==XENMEM_set_pod_target)?"set":"get",
> domid);
> - errno = -err;
> - err = -1;
> - }
> else
> err = 0;
>
>
>
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