RE: [PATCH v5 10/13] vdpa: Support reporting max device virtqueues

From: Si-Wei Liu <redacted>
Sent: Wednesday, December 22, 2021 7:31 AM

On 12/21/2021 9:20 AM, Eli Cohen wrote:

quoted

Add max_supported_vqs field to struct vdpa_mgmt_dev. Upstream drivers
need to feel this value according to the device capabilities.

This value is reported back in a netlink message when showing
management devices.

Example:

$ vdpa dev show

s/dev/mgmtdev/

and,

quoted

vdpa mgmtdev show

remove this line.

quoted

auxiliary/mlx5_core.sf.1:
   supported_classes net
   max_supported_vqs 256

It should be in same line.
Also please show the JSON output.

Not consistent with the example in patch #11 in the series.

quoted

Signed-off-by: Eli Cohen <redacted>
---
  drivers/vdpa/vdpa.c       | 3 +++
  include/linux/vdpa.h      | 1 +
  include/uapi/linux/vdpa.h | 1 +
  3 files changed, 5 insertions(+)

diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c index

eb223bec5209..4b649125a038 100644

--- a/drivers/vdpa/vdpa.c
+++ b/drivers/vdpa/vdpa.c

@@ -507,6 +507,9 @@ static int vdpa_mgmtdev_fill(const struct

vdpa_mgmt_dev *mdev, struct sk_buff *m

quoted

  		err = -EMSGSIZE;
  		goto msg_err;
  	}
+	if (nla_put_u16(msg, VDPA_ATTR_DEV_MGMTDEV_MAX_VQS,
+			mdev->max_supported_vqs))

It still needs a default value when the field is not explicitly filled in by the
driver.

Unlikely. This can be optional field to help user decide device max limit.
When max_supported_vqs is set to zero. Vdpa should omit exposing it to user space.

quoted

--- a/include/linux/vdpa.h
+++ b/include/linux/vdpa.h

@@ -447,6 +447,7 @@ struct vdpa_mgmt_dev {
  	const struct vdpa_mgmtdev_ops *ops;
  	const struct virtio_device_id *id_table;
  	u64 config_attr_mask;
+	u16 max_supported_vqs;

This breaks the natural alignment and create holes in the struct.
Please move it at the last entry in the struct after list.

There has been some talk/patches of rdma virtio device.
I anticipate such device to support more than 64K queues by nature of rdma.
It is better to keep max_supported_vqs as u32.

quoted

  	struct list_head list;
  };

diff --git a/include/uapi/linux/vdpa.h b/include/uapi/linux/vdpa.h
index db3738ef3beb..995257c6bf2a 100644
--- a/include/uapi/linux/vdpa.h
+++ b/include/uapi/linux/vdpa.h

@@ -44,6 +44,7 @@ enum vdpa_attr {
  	VDPA_ATTR_DEV_NET_CFG_MTU,		/* u16 */

  	VDPA_ATTR_DEV_NEGOTIATED_FEATURES,	/* u64 */
+	VDPA_ATTR_DEV_MGMTDEV_MAX_VQS,		/* u16 */
  	/* new attributes must be added above here */
  	VDPA_ATTR_MAX,
  };

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