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

[Jason Wang]

On 2020/8/31 下午7:16, 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>
> > ---
> >   net/vhost-vdpa.c | 24 +++++++++++++++++++-----
> >   qapi/net.json    |  5 ++++-
> >   2 files changed, 23 insertions(+), 6 deletions(-)
> >
> > diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
> > index 9a6f0b63d3..f6385cd264 100644
> > --- a/net/vhost-vdpa.c
> > +++ b/net/vhost-vdpa.c
> > @@ -206,20 +206,34 @@ int net_init_vhost_vdpa(const Netdev *netdev, const char 
> > *name,
> >                             (char *)name, errp)) {
> >           return -1;
> >       }
> > -    if (!opts->has_vhostdev) {
> > -        error_setg(errp, "vhost-vdpa requires vhostdev to be set");
> > +    if (!(opts->has_vhostdev ^ opts->has_fd)) {
> > +        error_setg(errp, "Vhost-vdpa requires either vhostdev or fd to be 
> > set");
> >           return -1;
> >       }
> >
> >       assert(name);
> >
> >       nc = qemu_new_net_client(&net_vhost_vdpa_info, peer, TYPE_VHOST_VDPA, 
> > name);
> > -    snprintf(nc->info_str, sizeof(nc->info_str), "vhostdev=%s", 
> > opts->vhostdev);
> > +    if (opts->has_vhostdev) {
> > +        snprintf(nc->info_str, sizeof(nc->info_str),
> > +                 "vhostdev=%s", opts->vhostdev);
> > +        vdpa_device_fd = qemu_open(opts->vhostdev, O_RDWR);
> > +        if (vdpa_device_fd == -1) {
> > +            error_setg(errp, "Fail to open vhost-vdpa device %s",
> > +                       opts->vhostdev);
> > +            return -errno;
> > +        }
> > +    } else {
> > +        snprintf(nc->info_str, sizeof(nc->info_str), "fd=%s", opts->fd);
> > +        vdpa_device_fd = monitor_fd_param(cur_mon, opts->fd, errp);
> > +        if (vdpa_device_fd == -1) {
> > +            return -1;
> > +        }
> > +    }
> >
> >       s = DO_UPCAST(VhostVDPAState, nc, nc);
> > -    vdpa_device_fd = qemu_open(opts->vhostdev, O_RDWR);
> >       if (vdpa_device_fd == -1) {
> > -        error_setg(errp, "Fail to open vhost-vdpa device %s", opts->vhostdev);
> > +
> >           return -errno;
> >       }
> >       s->vhost_vdpa.device_fd = vdpa_device_fd;
> > diff --git a/qapi/net.json b/qapi/net.json
> > index a2a94fad3e..5ad60c3045 100644
> > --- a/qapi/net.json
> > +++ 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.


Right, I forgot the fdset tricks.


Thanks



> Thanks
> Cindy