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.