Re: [Xen-devel] [PATCH v1 3/3] xen-livepatch: If hypervisor is not compiled with Livepatching

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

On 09/22/2016 11:12 AM, Konrad Rzeszutek Wilk wrote:
> On Thu, Sep 22, 2016 at 08:25:33AM +0100, Ross Lagerwall wrote:
> > On 09/21/2016 08:20 PM, Konrad Rzeszutek Wilk wrote:
> > > . print a better error code.
> > >
> > > Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> > > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > > ---
> > >  tools/misc/xen-livepatch.c | 7 +++++--
> > >  1 file changed, 5 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/tools/misc/xen-livepatch.c b/tools/misc/xen-livepatch.c
> > > index 2de04c0..f11e71f07f 100644
> > > --- a/tools/misc/xen-livepatch.c
> > > +++ b/tools/misc/xen-livepatch.c
> > > @@ -100,8 +100,11 @@ static int list_func(int argc, char *argv[])
> > >          rc = xc_livepatch_list(xch, MAX_LEN, idx, info, name, len, &done, 
> > > &left);
> > >          if ( rc )
> > >          {
> > > -            fprintf(stderr, "Failed to list %d/%d: %d(%s)!\n",
> > > -                    idx, left, errno, strerror(errno));
> > > +            if ( errno == ENOSYS )
> > > +                fprintf(stderr, "Hypervisor compiled without Xen 
> > > Livepatching!\n");
> > > +            else
> > > +                fprintf(stderr, "Failed to list %d/%d: %d(%s)!\n",
> > > +                        idx, left, errno, strerror(errno));
> > >              break;
> > >          }
> > >          if ( !idx )
> > You should save errno since you have an fprintf before you check it.
> I am missing something.
>
> Why would fprintf mess up 'errno' ?
> >
If the first fprintf fails for whatever reason (e.g. ENOSPC), then it 
will set errno and the subsequent check of errno afterwards will serve 
no purpose.
I have a patch to fix this issue for the rest of xen-livepatch.c, and 
will send it out shortly.
--
Ross Lagerwall

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