linux-kernel - Re: [PATCH 2/2] vdpa: vp_vdpa: don't use hard-coded maximum virtqueue size

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Date:   Mon, 5 Jul 2021 13:59:31 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        netdev@...r.kernel.org, xieyongji@...edance.com,
        stefanha@...hat.com
Subject: Re: [PATCH 2/2] vdpa: vp_vdpa: don't use hard-coded maximum
 virtqueue size

On Mon, Jul 05, 2021 at 03:29:47PM +0800, Jason Wang wrote:
> 
> 在 2021/7/5 下午3:26, Michael S. Tsirkin 写道:
> > On Mon, Jul 05, 2021 at 03:19:10PM +0800, Jason Wang wrote:
> > > This patch switch to read virtqueue size from the capability instead
> > > of depending on the hardcoded value. This allows the per virtqueue
> > > size could be advertised.
> > > 
> > > Signed-off-by: Jason Wang <jasowang@...hat.com>
> > So let's add an ioctl for this? It's really a bug we don't..
> 
> 
> As explained in patch 1. Qemu doesn't use VHOST_VDPA_GET_VRING_NUM actually.
> Instead it checks the result VHOST_VDPA_SET_VRING_NUM.
> 
> So I change VHOST_VDPA_GET_VRING_NUM to return the minimal size of all the
> virtqueues.
> 
> If you wish we can add a VHOST_VDPA_GET_VRING_NUM2, but I'm not sure it will
> have a user or not.
> 
> Thanks

Question is how do we know returning the minimal and not e.g. the max
size is the right thing to do?


> 
> > 
> > > ---
> > >   drivers/vdpa/virtio_pci/vp_vdpa.c | 6 ++++--
> > >   1 file changed, 4 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/vdpa/virtio_pci/vp_vdpa.c b/drivers/vdpa/virtio_pci/vp_vdpa.c
> > > index 2926641fb586..198f7076e4d9 100644
> > > --- a/drivers/vdpa/virtio_pci/vp_vdpa.c
> > > +++ b/drivers/vdpa/virtio_pci/vp_vdpa.c
> > > @@ -18,7 +18,6 @@
> > >   #include <linux/virtio_pci.h>
> > >   #include <linux/virtio_pci_modern.h>
> > > -#define VP_VDPA_QUEUE_MAX 256
> > >   #define VP_VDPA_DRIVER_NAME "vp_vdpa"
> > >   #define VP_VDPA_NAME_SIZE 256
> > > @@ -197,7 +196,10 @@ static void vp_vdpa_set_status(struct vdpa_device *vdpa, u8 status)
> > >   static u16 vp_vdpa_get_vq_num_max(struct vdpa_device *vdpa, u16 qid)
> > >   {
> > > -	return VP_VDPA_QUEUE_MAX;
> > > +	struct vp_vdpa *vp_vdpa = vdpa_to_vp(vdpa);
> > > +	struct virtio_pci_modern_device *mdev = &vp_vdpa->mdev;
> > > +
> > > +	return vp_modern_get_queue_size(mdev, qid);
> > >   }
> > >   static int vp_vdpa_get_vq_state(struct vdpa_device *vdpa, u16 qid,
> > > -- 
> > > 2.25.1