Re: [PATCH] libxc: avoid clobbering errno in xc_domain_pod_target()

[Juergen Gross <jgross@xxxxxxxx>]

On 09.12.21 11:26, Jan Beulich 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).
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> An alternative would be to let go of the DPRINTK() and leave errno and
> err alone altogether. 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.
>
> --- a/tools/libs/ctrl/xc_domain.c
> +++ b/tools/libs/ctrl/xc_domain.c
> @@ -1231,10 +1231,11 @@ static int xc_domain_pod_target(xc_inter
>   
>       if ( err < 0 )
>       {
> +        err = errno;
>           DPRINTF("Failed %s_pod_target dom %d\n",
>                   (op==XENMEM_set_pod_target)?"set":"get",
>                   domid);
> -        errno = -err;
> +        errno = err;
DPRINTF() won't change errno, so I think you should just drop the line
overwriting errno.


Juergen

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