Re: [Qemu-devel] [PATCH 00/12] Multiqueue virtio-net

[Anthony Liguori]

"Michael S. Tsirkin" <address@hidden> writes:

> On Wed, Jan 16, 2013 at 09:09:49AM -0600, Anthony Liguori wrote:
>> Jason Wang <address@hidden> writes:
>> 
>> > On 01/15/2013 03:44 AM, Anthony Liguori wrote:
>> >> Jason Wang <address@hidden> writes:
>> >>
>> >>> Hello all:
>> >>>
>> >>> This seires is an update of last version of multiqueue virtio-net 
>> >>> support.
>> >>>
>> >>> Recently, linux tap gets multiqueue support. This series implements basic
>> >>> support for multiqueue tap, nic and vhost. Then use it as an 
>> >>> infrastructure to
>> >>> enable the multiqueue support for virtio-net.
>> >>>
>> >>> Both vhost and userspace multiqueue were implemented for virtio-net, but
>> >>> userspace could be get much benefits since dataplane like parallized 
>> >>> mechanism
>> >>> were not implemented.
>> >>>
>> >>> User could start a multiqueue virtio-net card through adding a "queues"
>> >>> parameter to tap.
>> >>>
>> >>> ./qemu -netdev tap,id=hn0,queues=2,vhost=on -device 
>> >>> virtio-net-pci,netdev=hn0
>> >>>
>> >>> Management tools such as libvirt can pass multiple pre-created fds 
>> >>> through
>> >>>
>> >>> ./qemu -netdev tap,id=hn0,queues=2,fd=X,fd=Y -device
>> >>> virtio-net-pci,netdev=hn0
>> >> I'm confused/frightened that this syntax works.  You shouldn't be
>> >> allowed to have two values for the same property.  Better to have a
>> >> syntax like fd[0]=X,fd[1]=Y or something along those lines.
>> >
>> > Yes, but this what current a StringList type works for command line.
>> > Some other parameters such as dnssearch, hostfwd and guestfwd have
>> > already worked in this way. Looks like your suggestions need some
>> > extension on QemuOps visitor, maybe we can do this on top.
>> 
>> It's a silly syntax and breaks compatibility.  This is valid syntax:
>> 
>> -net tap,fd=3,fd=4
>> 
>> In this case, it means 'fd=4' because the last fd overwrites the first
>> one.
>> 
>> Now you've changed it to mean something else.  Having one thing mean
>> something in one context, but something else in another context is
>> terrible interface design.
>> 
>> Regards,
>> 
>> Anthony Liguori
>
> Aha so just renaming the field 'fds' would address this issue?

No, you still have the problem of different meanings.

-netdev tap,fd=X,fd=Y

-netdev tap,fds=X,fds=Y

Would have wildly different behavior.

Just do:

-netdev tap,fds=X:Y

And then we're staying consistent wrt the interpretation of multiple
properties of the same name.

Regards,

Anthony Liguori