From: Michael S. Tsirkin <mst@redhat.com>
Sent: Tuesday, July 26, 2022 3:52 PM

On Tue, Jul 26, 2022 at 03:56:32PM +0000, Parav Pandit wrote:

quoted

quoted

From: Zhu, Lingshan <redacted>
Sent: Tuesday, July 12, 2022 11:46 PM

quoted

When the user space which invokes netlink commands, detects that
_MQ

is not supported, hence it takes max_queue_pair = 1 by itself.
I think the kernel module have all necessary information and it is
the only one which have precise information of a device, so it
should answer precisely than let the user space guess. The kernel
module should be reliable than stay silent, leave the question to the user

space tool.

quoted

Kernel is reliable. It doesn’t expose a config space field if the field doesn’t exist

regardless of field should have default or no default.

quoted

User space should not guess either. User space gets to see if _MQ present/not

present. If _MQ present than get reliable data from kernel.

quoted

If _MQ not present, it means this device has one VQ pair.

Yes that's fine. And if we just didn't return anything without MQ that would be
fine.  But IIUC netlink reports the # of pairs regardless, it just puts 0 there.

I read it differently at [1] which checks for the MQ feature bit.

[1] https://elixir.bootlin.com/linux/latest/source/drivers/vdpa/vdpa.c#L825

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MST