Re: [PATCH] hw: virtio-mem: detach the element fromt the virtqueue when error occurs

[Li Qiang <liq3ea@gmail.com>]

David Hildenbrand <david@redhat.com> 于2020年8月14日周五 上午1:15写道：
>
> On 13.08.20 18:46, Li Qiang wrote:
>
> For now we use "virtio-mem:" for the subject, without the "hw: "part.
>
> > If error occurs while processing the virtio request we should call
> > 'virtqueue_detach_element' to detach the element from the virtqueue
> > before free the elem.
>
> What's the effect of this? In all cases we trigger a virtio_error(), so
> do we really have to bother?
>

Though the 'in_use' will be reset to 0 while reseting the virtio device.
The mapped sglist will not be unammped.
There maybe some undesired behavior.  CC Paolo to make a confirmation.

Thanks,
Li Qiang

> >
> > Signed-off-by: Li Qiang <liq3ea@163.com>
> > ---
> >  hw/virtio/virtio-mem.c | 13 +++++++------
> >  1 file changed, 7 insertions(+), 6 deletions(-)
> >
> > diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
> > index 7740fc613f..5ac6c3ec67 100644
> > --- a/hw/virtio/virtio-mem.c
> > +++ b/hw/virtio/virtio-mem.c
> > @@ -318,8 +318,7 @@ static void virtio_mem_handle_request(VirtIODevice *vdev, VirtQueue *vq)
> >          if (iov_to_buf(elem->out_sg, elem->out_num, 0, &req, len) < len) {
> >              virtio_error(vdev, "virtio-mem protocol violation: invalid request"
> >                           " size: %d", len);
> > -            g_free(elem);
> > -            return;
> > +            goto out_free;
> >          }
> >
> >          if (iov_size(elem->in_sg, elem->in_num) <
> > @@ -327,8 +326,7 @@ static void virtio_mem_handle_request(VirtIODevice *vdev, VirtQueue *vq)
> >              virtio_error(vdev, "virtio-mem protocol violation: not enough space"
> >                           " for response: %zu",
> >                           iov_size(elem->in_sg, elem->in_num));
> > -            g_free(elem);
> > -            return;
> > +            goto out_free;
> >          }
> >
> >          type = le16_to_cpu(req.type);
> > @@ -348,12 +346,15 @@ static void virtio_mem_handle_request(VirtIODevice *vdev, VirtQueue *vq)
> >          default:
> >              virtio_error(vdev, "virtio-mem protocol violation: unknown request"
> >                           " type: %d", type);
> > -            g_free(elem);
> > -            return;
> > +            goto out_free;
> >          }
> >
> >          g_free(elem);
> >      }
> > +
> > +out_free:
> > +    virtqueue_detach_element(vq, elem, 0);
> > +    g_free(elem);
> >  }
> >
> >  static void virtio_mem_get_config(VirtIODevice *vdev, uint8_t *config_data)
> >
>
>
> --
> Thanks,
>
> David / dhildenb
>