Re: [Qemu-devel] [PATCH v2 2/2] vhost: double check used memslots number

[Zhoujian (jay)]

[...]

> > ---
> >  hw/virtio/vhost.c | 27 +++++++++++++++++++++++----
> >  1 file changed, 23 insertions(+), 4 deletions(-)
> >
> > diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c index
> > 59a32e9..e45f5e2 100644
> > --- a/hw/virtio/vhost.c
> > +++ b/hw/virtio/vhost.c
> > @@ -1234,6 +1234,18 @@ static void vhost_virtqueue_cleanup(struct
> vhost_virtqueue *vq)
> >      event_notifier_cleanup(&vq->masked_notifier);
> >  }
> >
> > +static bool vhost_dev_used_memslots_is_exceeded(struct vhost_dev
> > +*hdev) {
> > +    if (hdev->vhost_ops->vhost_get_used_memslots() >
> > +        hdev->vhost_ops->vhost_backend_memslots_limit(hdev)) {
> > +        error_report("vhost backend memory slots limit is less"
> > +                " than current number of present memory slots");
> > +        return true;
> > +    }
> > +
> > +    return false;
> > +}
> > +
> >  int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
> >                     VhostBackendType backend_type, uint32_t
> > busyloop_timeout)  { @@ -1252,10 +1264,7 @@ int vhost_dev_init(struct
> > vhost_dev *hdev, void *opaque,
> >          goto fail;
> >      }
> >
> > -    if (hdev->vhost_ops->vhost_get_used_memslots() >
> > -        hdev->vhost_ops->vhost_backend_memslots_limit(hdev)) {
> > -        error_report("vhost backend memory slots limit is less"
> > -                " than current number of present memory slots");
> > +    if (vhost_dev_used_memslots_is_exceeded(hdev)) {
> why do you keep this check?
> it seems always be false
> 

If a vhost device has been already added successfully, i.e. its memory
Listener has been registered, i.e.
hdev->vhost_ops->vhost_set_used_memslots() has been called(used_memslots
is updated here),
then if we hotplug another same backend type vhost device,
hdev->vhost_ops->vhost_get_used_memslots() will not be 0(
used_memslots is the same for the same type backend vhost device), so it will
not always be false.

Regards,
Jay