Re: [PATCH v3 4/6] vhost-user: Add queue pair parameter throughout the network stack

On 12/11/25 08:01, Stefano Brivio wrote:

On Wed, 3 Dec 2025 19:54:32 +0100 Laurent Vivier wrote:

...

diff --git a/vu_common.c b/vu_common.c index b13b7c308fd8..80d9a30f6f71 100644 --- a/vu_common.c +++ b/vu_common.c @@ -196,11 +196,11 @@ static void vu_handle_tx(struct vu_dev *vdev, int index,

data = IOV_TAIL(elem[count].out_sg, elem[count].out_num, 0); if (IOV_DROP_HEADER(&data, struct virtio_net_hdr_mrg_rxbuf)) - tap_add_packet(vdev->context, &data, now); + tap_add_packet(vdev->context, 0, &data, now);

count++; } - tap_handler(vdev->context, now); + tap_handler(vdev->context, 0, now);

if (count) { int i; @@ -235,23 +235,26 @@ void vu_kick_cb(struct vu_dev *vdev, union epoll_ref ref, }

/** - * vu_send_single() - Send a buffer to the front-end using the RX virtqueue + * vu_send_single() - Send a buffer to the front-end using a specified virtqueue * @c: execution context + * @qpair: Queue pair on which to send the buffer * @buf: address of the buffer * @size: size of the buffer * * Return: number of bytes sent, -1 if there is an error */ -int vu_send_single(const struct ctx *c, const void *buf, size_t size) +int vu_send_single(const struct ctx *c, unsigned int qpair, const void *buf, size_t size) { struct vu_dev *vdev = c->vdev; - struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE]; struct vu_virtq_element elem[VIRTQUEUE_MAX_SIZE]; struct iovec in_sg[VIRTQUEUE_MAX_SIZE]; + struct vu_virtq *vq; size_t total; int elem_cnt; int i;

+ vq = &vdev->vq[qpair << 1];

<< 1 instead of * 2 is a bit surprising here, for a few seconds I thought you swapped qpair and 1.

Then I started thinking that somebody is likely to mix up (probably not you) indices of RX and TX queues at some point. So... what about some macros, say (let's see if I got it right this time):

#define VHOST_SEND_QUEUE(pair) ((pair) * 2) #define VHOST_RECV_QUEUE(pair) (pair)

I will. David had the same comment. TX and RX are from the point of view of guest, it's not obvious when we read passt code. I would prefer as David proposed to use, i.e. FROMGUEST and TOGUEST: #define VHOST_FROM_GUEST(qpair) ((qpair) * 2 + 1) #define VHOST_TO_GUEST(qpair) ((qpair) * 2)>

and:

#define VHOST_QUEUE_PAIR(q) ((q) % 2) ? (q) : (q) / 2)

I don't undestand the purpose of this one.

...are they correct? A short description or "Theory of operation" section somewhere with a recap of how queue indices are used would be nice to have.

And maybe also something explaining that 0 that's now appearing in argument lists:

#define VHOST_NO_QUEUE 0

It's not really NO_QUEUE, it's default queue pair, the queue pair 0 Thanks, Laurent