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

[Juergen Gross <jgross@xxxxxxxx>]

On 09.12.21 11:36, Juergen Gross wrote:
> 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.
In fact you added the 3rd layer of errno saving here. :-)

DPRINTF() and friends will save errno, and the underlying
xc_report*() functions will do so, too.

Writing a patch to remove the saving at the macro layer...


Juergen

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