On Tue, Jun 29, 2021 at 10:59:51AM +0800, Yongji Xie wrote: > On Mon, Jun 28, 2021 at 9:02 PM Stefan Hajnoczi wrote: > > > > On Tue, Jun 15, 2021 at 10:13:30PM +0800, Xie Yongji wrote: > > > +/* ioctls */ > > > + > > > +struct vduse_dev_config { > > > + char name[VDUSE_NAME_MAX]; /* vduse device name */ > > > + __u32 vendor_id; /* virtio vendor id */ > > > + __u32 device_id; /* virtio device id */ > > > + __u64 features; /* device features */ > > > + __u64 bounce_size; /* bounce buffer size for iommu */ > > > + __u16 vq_size_max; /* the max size of virtqueue */ > > > > The VIRTIO specification allows per-virtqueue sizes. A device can have > > two virtqueues, where the first one allows up to 1024 descriptors and > > the second one allows only 128 descriptors, for example. > > > > Good point! But it looks like virtio-vdpa/virtio-pci doesn't support > that now. All virtqueues have the same maximum size. I see struct vpda_config_ops only supports a per-device max vq size: u16 (*get_vq_num_max)(struct vdpa_device *vdev); virtio-pci supports per-virtqueue sizes because the struct virtio_pci_common_cfg->queue_size register is per-queue (controlled by queue_select). I guess this is a question for Jason: will vdpa will keep this limitation? If yes, then VDUSE can stick to it too without running into problems in the future. > > > + __u16 padding; /* padding */ > > > + __u32 vq_num; /* the number of virtqueues */ > > > + __u32 vq_align; /* the allocation alignment of virtqueue's metadata */ > > > > I'm not sure what this is? > > > > This will be used by vring_create_virtqueue() too. If there is no official definition for the meaning of this value then "/* same as vring_create_virtqueue()'s vring_align parameter */" would be clearer. That way the reader knows what to research in order to understand how this field works. I don't remember but maybe it was used to support vrings when the host/guest have non-4KB page sizes. I wonder if anyone has an official definition for this value?