Re: [PATCH v2 2/3] vu_handle_tx: Pass actual remaining out_sg capacity to vu_queue_pop()

[Stefano Brivio <sbrivio@redhat.com>]

On Fri, 13 Mar 2026 19:26:17 +0100
Laurent Vivier <lvivier@redhat.com> wrote:

> In vu_handle_tx(), pass the actual remaining iovec capacity
> (ARRAY_SIZE(out_sg) - out_sg_count) to vu_queue_pop() rather than a
> fixed VU_MAX_TX_BUFFER_NB.
> 
> This enables dynamic allocation of iovec entries to each element rather
> than reserving a fixed number of slots per descriptor.
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---
>  vu_common.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/vu_common.c b/vu_common.c
> index 4d809ac38a4b..ed0033d6bb11 100644
> --- a/vu_common.c
> +++ b/vu_common.c
> @@ -20,8 +20,6 @@
>  #include "migrate.h"
>  #include "epoll_ctl.h"
>  
> -#define VU_MAX_TX_BUFFER_NB	2
> -
>  /**
>   * vu_packet_check_range() - Check if a given memory zone is contained in
>   * 			     a mapped guest memory region
> @@ -177,13 +175,14 @@ static void vu_handle_tx(struct vu_dev *vdev, int index,
>  
>  	count = 0;
>  	out_sg_count = 0;
> -	while (count < VIRTQUEUE_MAX_SIZE &&
> -	       out_sg_count + VU_MAX_TX_BUFFER_NB <= VIRTQUEUE_MAX_SIZE) {
> -		int ret;
> +	while (count < ARRAY_SIZE(elem) &&
> +	       out_sg_count < ARRAY_SIZE(out_sg)) {

Nit: you could do this now:

	while (count < ARRAY_SIZE(elem) && out_sg_count < ARRAY_SIZE(out_sg)) {

I still need a bit of time to review 3/3, if you don't need to re-spin
for other reasons I can also fix this up on merge.

>  		struct iov_tail data;
> +		int ret;
>  
>  		ret = vu_queue_pop(vdev, vq, &elem[count], NULL, 0,
> -				   &out_sg[out_sg_count], VU_MAX_TX_BUFFER_NB);
> +				   &out_sg[out_sg_count],
> +				   ARRAY_SIZE(out_sg) - out_sg_count);
>  		if (ret < 0)
>  			break;
>  		out_sg_count += elem[count].out_num;

-- 
Stefano