[PATCH RFC 3/3] vhost-vdpa: uAPI to get dedicated descriptor group id

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With _F_DESC_ASID backend feature, the device can now support the
VHOST_VDPA_GET_VRING_DESC_GROUP ioctl, and it may expose the descriptor
table (including avail and used ring) in a different group than the
buffers it contains. This new uAPI will fetch the group ID of the
descriptor table.

Signed-off-by: Si-Wei Liu <si-wei.liu@xxxxxxxxxx>
---
 drivers/vhost/vdpa.c       | 10 ++++++++++
 include/uapi/linux/vhost.h |  8 ++++++++
 2 files changed, 18 insertions(+)

diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
index f2e5dce..eabac06 100644
--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c
@@ -602,6 +602,16 @@ static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
 		else if (copy_to_user(argp, &s, sizeof(s)))
 			return -EFAULT;
 		return 0;
+	case VHOST_VDPA_GET_VRING_DESC_GROUP:
+		if (!vhost_vdpa_has_desc_group(v))
+			return -EOPNOTSUPP;
+		s.index = idx;
+		s.num = ops->get_vq_desc_group(vdpa, idx);
+		if (s.num >= vdpa->ngroups)
+			return -EIO;
+		else if (copy_to_user(argp, &s, sizeof(s)))
+			return -EFAULT;
+		return 0;
 	case VHOST_VDPA_SET_GROUP_ASID:
 		if (copy_from_user(&s, argp, sizeof(s)))
 			return -EFAULT;
diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
index f5c48b6..05faad2 100644
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h
@@ -219,4 +219,12 @@
  */
 #define VHOST_VDPA_RESUME		_IO(VHOST_VIRTIO, 0x7E)
 
+/* Get the dedicated group for the descriptor table of a virtqueue:
+ * read index, write group in num.
+ * The virtqueue index is stored in the index field of vhost_vring_state.
+ * The group id for the descriptor table of this specific virtqueue
+ * is returned via num field of vhost_vring_state.
+ */
+#define VHOST_VDPA_GET_VRING_DESC_GROUP	_IOWR(VHOST_VIRTIO, 0x7F,	\
+					      struct vhost_vring_state)
 #endif
-- 
1.8.3.1

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