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

[Jason Wang <jasowang@redhat.com>]

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
>
>