Virtualization - Jul 2022 - [PATCH V3 5/6] vDPA: answer num of queue pairs = 1 to userspace when VIRTIO_NET_F_MQ == 0

> From: Zhu, Lingshan <lingshan.zhu at intel.com>
> Sent: Tuesday, July 26, 2022 10:53 PM
> 
> On 7/27/2022 10:17 AM, Parav Pandit wrote:
> >> From: Zhu, Lingshan <lingshan.zhu at intel.com>
> >> Sent: Tuesday, July 26, 2022 10:15 PM
> >>
> >> On 7/26/2022 11:56 PM, Parav Pandit wrote:
> >>>> From: Zhu, Lingshan <lingshan.zhu at intel.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.
> >> so when you know it is one queue pair, you should answer one, not
try
> >> to guess.
> >>> 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.
> >> it is still a guess, right? And all user space tools implemented
this
> >> feature need to guess
> > No. it is not a guess.
> > It is explicitly checking the _MQ feature and deriving the value.
> > The code you proposed will be present in the user space.
> > It will be uniform for _MQ and 10 other features that are present now
and
> in the future.
> MQ and other features like RSS are different. If there is no _RSS_XX, there
> are no attributes like max_rss_key_size, and there is not a default value.
> But for MQ, we know it has to be 1 wihtout _MQ.
"we" = user space.
To keep the consistency among all the config space fields.
> > For feature X, kernel reports default and for feature Y, kernel skip
> reporting it, because there is no default. <- This is what we are trying
to
> avoid here.
> Kernel reports one queue pair because there is actually one.
> >

On Wed, Jul 27, 2022 at 03:47:35AM +0000, Parav Pandit
wrote:
> 
> > From: Zhu, Lingshan <lingshan.zhu at intel.com>
> > Sent: Tuesday, July 26, 2022 10:53 PM
> > 
> > On 7/27/2022 10:17 AM, Parav Pandit wrote:
> > >> From: Zhu, Lingshan <lingshan.zhu at intel.com>
> > >> Sent: Tuesday, July 26, 2022 10:15 PM
> > >>
> > >> On 7/26/2022 11:56 PM, Parav Pandit wrote:
> > >>>> From: Zhu, Lingshan <lingshan.zhu at intel.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.
> > >> so when you know it is one queue pair, you should answer one,
not try
> > >> to guess.
> > >>> 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.
> > >> it is still a guess, right? And all user space tools
implemented this
> > >> feature need to guess
> > > No. it is not a guess.
> > > It is explicitly checking the _MQ feature and deriving the value.
> > > The code you proposed will be present in the user space.
> > > It will be uniform for _MQ and 10 other features that are present
now and
> > in the future.
> > MQ and other features like RSS are different. If there is no _RSS_XX,
there
> > are no attributes like max_rss_key_size, and there is not a default
value.
> > But for MQ, we know it has to be 1 wihtout _MQ.
> "we" = user space.
> To keep the consistency among all the config space fields.
Actually I looked and the code some more and I'm puzzled:


	struct virtio_net_config config = {};
	u64 features;
	u16 val_u16;

	vdpa_get_config_unlocked(vdev, 0, &config, sizeof(config));

	if (nla_put(msg, VDPA_ATTR_DEV_NET_CFG_MACADDR, sizeof(config.mac),
		    config.mac))
		return -EMSGSIZE;


Mac returned even without VIRTIO_NET_F_MAC


	val_u16 = le16_to_cpu(config.status);
	if (nla_put_u16(msg, VDPA_ATTR_DEV_NET_STATUS, val_u16))
		return -EMSGSIZE;


status returned even without VIRTIO_NET_F_STATUS

	val_u16 = le16_to_cpu(config.mtu);
	if (nla_put_u16(msg, VDPA_ATTR_DEV_NET_CFG_MTU, val_u16))
		return -EMSGSIZE;


MTU returned even without VIRTIO_NET_F_MTU


What's going on here?


-- 
MST