netdev - RE: [PATCH V3 5/6] vDPA: answer num of queue pairs = 1 to userspace when VIRTIO_NET_F

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Message-ID: <PH0PR12MB54815985C202E81122459DFFDC949@PH0PR12MB5481.namprd12.prod.outlook.com>
Date:   Tue, 26 Jul 2022 15:56:32 +0000
From:   Parav Pandit <parav@...dia.com>
To:     "Zhu, Lingshan" <lingshan.zhu@...el.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "mst@...hat.com" <mst@...hat.com>
CC:     "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "xieyongji@...edance.com" <xieyongji@...edance.com>,
        "gautam.dawar@....com" <gautam.dawar@....com>
Subject: RE: [PATCH V3 5/6] vDPA: answer num of queue pairs = 1 to userspace
 when VIRTIO_NET_F_MQ == 0


> From: Zhu, Lingshan <lingshan.zhu@...el.com>
> Sent: Tuesday, July 12, 2022 11:46 PM
> > 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.
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.
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.
If _MQ not present, it means this device has one VQ pair.