Re: [dpdk-dev] [PATCH v2] net/virtio: fix virtio-user init when using existing tap

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 9/29/21 15:19, Ferruh Yigit wrote:
> On 9/28/2021 9:51 AM, David Marchand wrote:
>> When attaching to an existing mono queue tap, the virtio-user was not
>> reporting that the virtio device was not properly initialised which
>> prevented from starting the port later.
>>
>> $ ip tuntap add test mode tap
>> $ dpdk-testpmd --vdev \
>>    net_virtio_user0,iface=test,path=/dev/vhost-net,queues=2 -- -i
>>
>> ...
>> virtio_user_dev_init_mac(): (/dev/vhost-net) No valid MAC in devargs or
>> device, use random
>> vhost_kernel_open_tap(): TUNSETIFF failed: Invalid argument
>> vhost_kernel_enable_queue_pair(): fail to open tap for vhost kernel
>> virtio_user_start_device(): (/dev/vhost-net) Failed to start device
>> ...
>> Configuring Port 0 (socket 0)
>> vhost_kernel_open_tap(): TUNSETIFF failed: Invalid argument
>> vhost_kernel_enable_queue_pair(): fail to open tap for vhost kernel
>> virtio_set_multiple_queues(): Multiqueue configured but send command
>> failed, this is too late now...
>> Fail to start port 0: Invalid argument
>> Please stop the ports first
>> Done
>>
>> The virtio-user with vhost-kernel backend was going through a lot
>> of complications to initialise tap fds only when using them.
>>
>> For each qp enabled for the first time, a tapfd was created via
>> TUNSETIFF with unneeded additional steps (see below) and then mapped to
>> the right qp in the vhost-net backend.
>> Unneeded steps (as long as it has been done once for the port):
>> - tap features were queried while this is a constant on a running
>>    system,
>> - the device name in DPDK was updated,
>> - the mac address of the tap was set,
>>
>> On subsequent qps state change, the vhost-net backend fd mapping was
>> updated and the associated queue/tapfd were disabled/enabled via
>> TUNSETQUEUE.
>>
>> Now, this patch simplifies the whole logic by keeping all tapfds opened
>> and in enabled state (from the tap point of view) at all time.
>>
>> Unused ioctl defines are removed.
>>
>> Tap features are validated earlier to fail initialisation asap.
>> Tap name discovery and mac address configuration are moved when
>> configuring qp 0.
>>
>> To support attaching to mono queue tap, the virtio-user driver now tries
>> to attach in multi queue first, then fallbacks to mono queue.
>>
>> Finally (but this is more for consistency), VIRTIO_NET_F_MQ feature is
>> exposed only if the underlying tap supports multi queue.
>>
>> Signed-off-by: David Marchand <david.marchand@redhat.com>
> 
> Do we want to backport this patch? If so can you please provide a fixes tag?
> 

No, we don't want to backport it.

Thanks,
Maxime