Re: [PATCH 1/3] vhost-user: Fix VHOST_USER_GET_QUEUE_NUM to return number of queues

[David Gibson <david@gibson.dropbear.id.au>]

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On Fri, Sep 05, 2025 at 05:49:33PM +0200, Laurent Vivier wrote:
> The vhost-user specification states that VHOST_USER_GET_QUEUE_NUM should
> return the maximum number of queues supported by the back-end, not the
> number of virtqueues. Since each queue pair consists of RX and TX
> virtqueues, we need to divide VHOST_USER_MAX_QUEUES by 2 to get the
> correct queue count.
> 
> Also rename VHOST_USER_MAX_QUEUES to VHOST_USER_MAX_VQS throughout the
> codebase to better reflect that it represents the maximum number of
> virtqueues, not queue pairs.
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  vhost_user.c | 16 +++++++++-------
>  virtio.h     |  4 ++--
>  2 files changed, 11 insertions(+), 9 deletions(-)
> 
> diff --git a/vhost_user.c b/vhost_user.c
> index f97ec6064cac..fa343a86fac2 100644
> --- a/vhost_user.c
> +++ b/vhost_user.c
> @@ -345,7 +345,7 @@ static void vu_set_enable_all_rings(struct vu_dev *vdev, bool enable)
>  {
>  	uint16_t i;
>  
> -	for (i = 0; i < VHOST_USER_MAX_QUEUES; i++)
> +	for (i = 0; i < VHOST_USER_MAX_VQS; i++)
>  		vdev->vq[i].enable = enable;
>  }
>  
> @@ -477,7 +477,7 @@ static bool vu_set_mem_table_exec(struct vu_dev *vdev,
>  		close(vmsg->fds[i]);
>  	}
>  
> -	for (i = 0; i < VHOST_USER_MAX_QUEUES; i++) {
> +	for (i = 0; i < VHOST_USER_MAX_VQS; i++) {
>  		if (vdev->vq[i].vring.desc) {
>  			if (map_ring(vdev, &vdev->vq[i]))
>  				die("remapping queue %d during setmemtable", i);
> @@ -770,7 +770,7 @@ static void vu_check_queue_msg_file(struct vhost_user_msg *vmsg)
>  	bool nofd = vmsg->payload.u64 & VHOST_USER_VRING_NOFD_MASK;
>  	int idx = vmsg->payload.u64 & VHOST_USER_VRING_IDX_MASK;
>  
> -	if (idx >= VHOST_USER_MAX_QUEUES)
> +	if (idx >= VHOST_USER_MAX_VQS)
>  		die("Invalid vhost-user queue index: %u", idx);
>  
>  	if (nofd) {
> @@ -939,7 +939,9 @@ static bool vu_get_queue_num_exec(struct vu_dev *vdev,
>  {
>  	(void)vdev;
>  
> -	vmsg_set_reply_u64(vmsg, VHOST_USER_MAX_QUEUES);
> +	vmsg_set_reply_u64(vmsg, VHOST_USER_MAX_VQS / 2);
> +
> +	debug("VHOST_USER_MAX_VQS  %u", VHOST_USER_MAX_VQS / 2);
>  
>  	return true;
>  }
> @@ -960,7 +962,7 @@ static bool vu_set_vring_enable_exec(struct vu_dev *vdev,
>  	debug("State.index:  %u", idx);
>  	debug("State.enable: %u", enable);
>  
> -	if (idx >= VHOST_USER_MAX_QUEUES)
> +	if (idx >= VHOST_USER_MAX_VQS)
>  		die("Invalid vring_enable index: %u", idx);
>  
>  	vdev->vq[idx].enable = enable;
> @@ -1052,7 +1054,7 @@ void vu_init(struct ctx *c)
>  
>  	c->vdev = &vdev_storage;
>  	c->vdev->context = c;
> -	for (i = 0; i < VHOST_USER_MAX_QUEUES; i++) {
> +	for (i = 0; i < VHOST_USER_MAX_VQS; i++) {
>  		c->vdev->vq[i] = (struct vu_virtq){
>  			.call_fd = -1,
>  			.kick_fd = -1,
> @@ -1075,7 +1077,7 @@ void vu_cleanup(struct vu_dev *vdev)
>  {
>  	unsigned int i;
>  
> -	for (i = 0; i < VHOST_USER_MAX_QUEUES; i++) {
> +	for (i = 0; i < VHOST_USER_MAX_VQS; i++) {
>  		struct vu_virtq *vq = &vdev->vq[i];
>  
>  		vq->started = false;
> diff --git a/virtio.h b/virtio.h
> index b55cc4042521..12caaa0b6def 100644
> --- a/virtio.h
> +++ b/virtio.h
> @@ -88,7 +88,7 @@ struct vu_dev_region {
>  	uint64_t mmap_addr;
>  };
>  
> -#define VHOST_USER_MAX_QUEUES 2
> +#define VHOST_USER_MAX_VQS 2
>  
>  /*
>   * Set a reasonable maximum number of ram slots, which will be supported by
> @@ -121,7 +121,7 @@ struct vdev_memory {
>  struct vu_dev {
>  	struct ctx *context;
>  	struct vdev_memory memory;
> -	struct vu_virtq vq[VHOST_USER_MAX_QUEUES];
> +	struct vu_virtq vq[VHOST_USER_MAX_VQS];
>  	uint64_t features;
>  	uint64_t protocol_features;
>  	int log_call_fd;
> -- 
> 2.50.1
> 

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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