在 2021/6/24 下午2:29, Parav Pandit 写道:
From: Jason Wang <jasowang@xxxxxxxxxx>
Sent: Thursday, June 24, 2021 11:13 AM
在 2021/6/23 下午12:22, Parav Pandit 写道:
From: Jason Wang <jasowang@xxxxxxxxxx>
Sent: Wednesday, June 23, 2021 9:39 AM
在 2021/6/22 下午10:03, Parav Pandit 写道:
Is it better to use a separate enum for net specific attributes?
Yes, because they are only net specific.
I guess it is related to your below question.
Another question (sorry if it has been asked before). Can we simply
return the config (binary) to the userspace, then usespace can use
the existing uAPI like virtio_net_config plus the feature to
explain the
config?
We did discuss in v2.
Usually returning the whole blob and parsing is not desired via netlink.
Returning individual fields give the full flexibility to return only
the valid
fields.
Otherwise we need to implement another bitmask too to tell which
fields
from the struct are valid and share with user space.
Returning individual fields is the widely used approach.
The main concerns are:
1) The blob will be self contained if it was passed with the
negotiated features, so we don't need bitmask.
Which fields of the struct are valid is told by additional fields.
2) Using individual fields means it must duplicate the config fields
of every virtio devices
Mostly no. if there are common config fields across two device types,
they would be named as
VDPA_ATTR_DEV_CFG_*
Net specific will be,
VDPA_ATTR_DEV_NET_CFG_*
Block specific, will be,
VDPA_ATTR_DEV_BLK_CFG_*
I meant it looks like VDPA_ATTR_DEV_NET will duplicate all the fields of:
struct virtio_net_config;
And VDPA_ATTR_DEV_BLOCK will duplicate all the fields of
struct virtio_blk_config; which has ~21 fields.
And we had a plenty of other types of virtio devices.
Consider we had a mature set of virtio specific uAPI for config space.
It would be a burden if we need an unnecessary translation layer of netlink in
the middle:
[vDPA parent (virtio_net_config)] <-> [netlink (VDPA_ATTR_DEV_NET_XX)]
<-> [userspace (VDPA_ATTR_DEV_NET_XX)]
<-> [ user (virtio_net_config)]
This translation is not there. We show relevant net config fields as VDPA_ATTR_DEV_NET individually.
It is not a binary dump which is harder for users to parse and make any use of it.
The is done implicitly, user needs to understand the semantic of
virtio_net_config and map the individual fields to the vdpa tool
sub-command.
It is only one level of translation from virtio_net_config (kernel) -> netlink vdpa fields.
It is similar to 'struct netdevice' -> rtnl info fields.
I think not, the problem is that the netdevice is not a part of uAPI but
virtio_net_config is.
If we make netlink simply a transport, it would be much easier. And we had
the chance to unify the logic of build_config() and set_config() in the driver.
How? We need bit mask to tell that out of 21 fields which fields to update and which not.
And that is further mixed with offset and length.
So set_config() could be called from userspace, so did build_config().
The only difference is:
1) they're using different transport, ioctl vs netlink
2) build_config() is only expected to be called by the management tool
If qemu works well via set_config ioctl, netlink should work as well.
Btw, what happens if management tool tries to modify the mac of vDPA
when the device is already used by the driver?
And actually, it's not the binary blob since uapi clearly define the
format (e.g struct virtio_net_config), can we find a way to use that?
E.g introduce device/net specific command and passing the blob with
length and negotiated features.
Length may change in future, mostly expand. And parsing based on length
is not such a clean way.
Length is only for legal checking. The config is self contained with:
Unlikely. When structure size increases later, the parsing will change based on the length.
Because older kernel would return shorter length with older iproute2 tool.
This is fine since the older kernel only support less features. The only
possible issue if the old iproute 2 runs on new kernel. With the current
proposal, it may cause some config fields can't not be showed.
I think it might be useful to introduce a command to simply dump the
config space.
So user space always have to deal and have nasty parsing/typecasting based on the length.
That's how userspace (Qemu) is expected to work now. The userspace
should determine the semantic of the fields based on the features.
Differentiate config fields doesn't help much, e.g userspace still need
to differ LINK_UP and ANNOUNCE for the status field.
1) device id
2) features
Parsing fields require knowledge of features as well and application needs
to make multiple netlink calls to parse the config space.
I think we don't care about the performance in this case. It's about three
netlink calls:
Its not about performance. By the time 1st call is made, features got updated and it is out of sync with config.
1) get config
2) get device id
3) get features
This requires using features from 3rd netlink output to decode output of 1st netlink output.
Which is a bit odd of netlink.
Other netlink nla_put() probably sending whole structure doesn’t need to do it.
Well, we can pack them all into a single skb isn't it? (probably with a
config len).
For build config, it's only one
1) build config
I prefer to follow rest of the kernel style to return self contained
invidividual fields.
But I saw a lot of kernel codes choose to use e.g nla_put() directly with
module specific structure.
It might be self-contained structure that probably has not found the need to expand.
I think it's just a matter of putting the config length with the config
data. Note that we've already had .get_config_size() ops for validating
inputs through VHOST_SET_CONFIG/VHOST_GET_CONFIG.
Thanks
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