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

[Cindy Lu]

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.

Thanks
Cindy