Re: [PATCH 9/9] vhost-vdpa: allow pre-opend file descriptor

[Eric Blake]

On 8/31/20 6:16 AM, Cindy Lu wrote:
> On Mon, 31 Aug 2020 at 16:30, Jason Wang <jasowang@redhat.com> wrote:
> > This patch allows to initialize vhost-vdpa network backend with pre
> > opened vhost-vdpa file descriptor. This is useful for running
> > unprivileged qemu through libvirt.
> >
> > Cc: Eric Blake <eblake@redhat.com>
> > Cc: Markus Armbruster <armbru@redhat.com>
> > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > ---

> > +++ b/qapi/net.json
> > @@ -442,12 +442,15 @@
> >   # @queues: number of queues to be created for multiqueue vhost-vdpa
> >   #          (default: 1)
> >   #
> > +# @fd: file descriptor of an already opened vhost-vdpa (since 5.2)
> > +#
> >   # Since: 5.1
> >   ##
> >   { 'struct': 'NetdevVhostVDPAOptions',
> >     'data': {
> >       '*vhostdev':     'str',
> > -    '*queues':       'int' } }
> > +    '*queues':       'int',
> > +    '*fd':           'str' } }
> >
> >   ##
> >   # @NetClientDriver:
> > --
> > 2.20.1
> I think the latest  code supported this part.
> you can pass a pre open file descriptor to it via the add-fd QMP
> command to /dev/fdset/NNN, and then pass the string
> "/dev/fdset/NNN" as vhostdev.  so we don't need a special fd parameter here.

Correct - the 'vhostdev' parameter + magic filename is all the more that 
is needed to access a pre-opened fd, so no 'fd' parameter should be added.

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org