On Wed, Jul 27, 2022 at 03:09:43AM -0700, Si-Wei Liu wrote: > > > On 7/27/2022 2:01 AM, Michael S. Tsirkin wrote: > > On Wed, Jul 27, 2022 at 12:50:33AM -0700, Si-Wei Liu wrote: > > > > > > On 7/26/2022 11:01 PM, Michael S. Tsirkin wrote: > > > > On Wed, Jul 27, 2022 at 03:47:35AM +0000, Parav Pandit wrote: > > > > > > From: Zhu, Lingshan <[email protected]> > > > > > > Sent: Tuesday, July 26, 2022 10:53 PM > > > > > > > > > > > > On 7/27/2022 10:17 AM, Parav Pandit wrote: > > > > > > > > From: Zhu, Lingshan <[email protected]> > > > > > > > > Sent: Tuesday, July 26, 2022 10:15 PM > > > > > > > > > > > > > > > > On 7/26/2022 11:56 PM, Parav Pandit wrote: > > > > > > > > > > From: Zhu, Lingshan <[email protected]> > > > > > > > > > > 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? > > > > > > > > > > > I guess this is spec thing (historical debt), I vaguely recall these > > > fields > > > are always present in config space regardless the existence of > > > corresponding > > > feature bit. > > > > > > -Siwei > > Nope: > > > > 2.5.1 Driver Requirements: Device Configuration Space > > > > ... > > > > For optional configuration space fields, the driver MUST check that the > > corresponding feature is offered > > before accessing that part of the configuration space. > Well, this is driver side of requirement.
Well driver and device are the only two entities in the spec. > As this interface is for host > admin tool to query or configure vdpa device, we don't have to wait until > feature negotiation is done on guest driver to extract vdpa > attributes/parameters, say if we want to replicate another vdpa device with > the same config on migration destination. I think what may need to be fix is > to move off from using .vdpa_get_config_unlocked() which depends on feature > negotiation. And/or expose config space register values through another set > of attributes. > > -Siwei > > Sounds like something that might use the proposed admin queue maybe. Hope that makes progress ... -- MST _______________________________________________ Virtualization mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/virtualization
