Re: [Qemu-devel] [PATCH 15/18] xen: add a mechanism to automatically create XenDevice-s...

[Paul Durrant <Paul.Durrant@citrix.com>]

> -----Original Message-----
> From: Anthony PERARD [mailto:anthony.perard@citrix.com]
> Sent: 06 December 2018 15:24
> To: Paul Durrant <Paul.Durrant@citrix.com>
> Cc: qemu-block@nongnu.org; qemu-devel@nongnu.org; xen-
> devel@lists.xenproject.org; Stefano Stabellini <sstabellini@kernel.org>
> Subject: Re: [PATCH 15/18] xen: add a mechanism to automatically create
> XenDevice-s...
> 
> On Thu, Dec 06, 2018 at 12:36:52PM +0000, Paul Durrant wrote:
> > > -----Original Message-----
> > > From: Anthony PERARD [mailto:anthony.perard@citrix.com]
> > > Sent: 04 December 2018 15:35
> > >
> > > On Wed, Nov 21, 2018 at 03:12:08PM +0000, Paul Durrant wrote:
> > > > +    xenbus->backend_watch =
> > > > +        xen_bus_add_watch(xenbus, "", /* domain root node */
> > > > +                          "backend", xen_bus_enumerate, xenbus,
> > > &local_err);
> > > > +    if (local_err) {
> > > > +        error_propagate(errp, local_err);
> > > > +        error_prepend(errp, "failed to set up enumeration watch:
> ");
> > >
> > > You should use error_propagate_prepend instead
> > > error_propagate;error_prepend. And it looks like there is the same
> > > mistake in other patches that I haven't notice.
> > >
> >
> > Oh, I didn't know about that one either... I've only seen the separate
> calls used elsewhere.
> 
> That information is all in "include/qapi/error.h", if you which to know
> more on how to use Error.
> 

Thanks.

> > > Also you probably want goto fail here.
> > >
> >
> > Not sure about that. Whilst the bus scan won't happen, it doesn't mean
> devices can't be added via QMP.
> 
> In that case, don't modify errp, and use error_reportf_err instead, or
> warn_reportf_err (then local_err = NULL, in case it is reused in a
> future modification of the function).
> 
> Setting errp (with error_propagate) means that the function failed, and
> QEMU is going to exit(1), because of qdev_init_nofail call in
> xen_bus_init.

Ah, good point. I'll wait for more feedback on v2 and then fix in v3.

  Paul