On Tue, Jul 16, 2024 at 5:05 AM Zhao Liu <zhao1....@intel.com> wrote:
>
> On Mon, Jul 15, 2024 at 11:01:08PM +0200, Eugenio Perez Martin wrote:
> > Date: Mon, 15 Jul 2024 23:01:08 +0200
> > From: Eugenio Perez Martin <epere...@redhat.com>
> > Subject: Re: [PATCH] hw/virtio/vdpa-dev: Check returned value instead of
> > dereferencing @errp
> >
> > On Mon, Jul 15, 2024 at 11:45 AM Zhao Liu <zhao1....@intel.com> wrote:
> > >
> > > As the comment in qapi/error, dereferencing @errp requires
> > > ERRP_GUARD():
> > >
> > > * = Why, when and how to use ERRP_GUARD() =
> > > *
> > > * Without ERRP_GUARD(), use of the @errp parameter is restricted:
> > > * - It must not be dereferenced, because it may be null.
> > > ...
> > > * ERRP_GUARD() lifts these restrictions.
> > > *
> > > * To use ERRP_GUARD(), add it right at the beginning of the function.
> > > * @errp can then be used without worrying about the argument being
> > > * NULL or &error_fatal.
> > > *
> > > * Using it when it's not needed is safe, but please avoid cluttering
> > > * the source with useless code.
> > >
> > > Though vhost_vdpa_device_realize() is called at DeviceClass.realize()
> > > context and won't get NULL @errp, it's still better to follow the
> > > requirement to add the ERRP_GUARD().
> > >
> > > But qemu_open() and vhost_vdpa_device_get_u32()'s return values can
> > > distinguish between successful and unsuccessful calls, so check the
> > > return values directly without dereferencing @errp, which eliminates
> > > the need of ERRP_GUARD().
> > >
> > > Cc: "Michael S. Tsirkin" <m...@redhat.com>
> > > Cc: "Eugenio Pérez" <epere...@redhat.com>
> > > Cc: Jason Wang <jasow...@redhat.com>
> > > Signed-off-by: Zhao Liu <zhao1....@intel.com>
> > > ---
> > > hw/virtio/vdpa-dev.c | 11 ++++++-----
> > > 1 file changed, 6 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/hw/virtio/vdpa-dev.c b/hw/virtio/vdpa-dev.c
> > > index 64b96b226c39..7b439efdc1d3 100644
> > > --- a/hw/virtio/vdpa-dev.c
> > > +++ b/hw/virtio/vdpa-dev.c
> > > @@ -50,6 +50,7 @@ vhost_vdpa_device_get_u32(int fd, unsigned long int
> > > cmd, Error **errp)
> > >
> > > static void vhost_vdpa_device_realize(DeviceState *dev, Error **errp)
> > > {
> > > + ERRP_GUARD();
> >
> > Good catch, thank you! But removing the err dereferencing eliminates
> > the need for ERRP_GUARD(), doesn't it?
> >
>
> Thanks Eugenio! You're right and I forgot to delete it. I'll post a new
> version.
>
>
Good! With that removed,
Acked-by: Eugenio Pérez <epere...@redhat.com>
Thanks!
