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From: Laurent Vivier <lvivier@redhat.com>
To: David Gibson <david@gibson.dropbear.id.au>,
	Stefano Brivio <sbrivio@redhat.com>,
	passt-dev@passt.top
Subject: Re: [PATCH] tcp_vu: head_cnt need not be global
Date: Tue, 18 Feb 2025 09:01:30 +0100	[thread overview]
Message-ID: <53e1b351-da19-4491-b438-1e77e0dc836c@redhat.com> (raw)
In-Reply-To: <20250218025013.1035148-1-david@gibson.dropbear.id.au>

On 18/02/2025 03:50, David Gibson wrote:
> head_cnt is a global variable which tracks how many entries in head[] are
> currently used.  The fact that it's global obscures the fact that the
> lifetime over which it has a meaningful value is quite short: a single
> call to of tcp_vu_data_from_sock().
> 
> Make it a local to tcp_vu_data_from_sock() to make that lifetime clearer.
> We keep the head[] array global for now - although technically it has the
> same valid lifetime - because it's large enough we might not want to put
> it on the stack.

We can make the array local but on the heap using a static declaration in the function.

Reviewed-by: Laurent Vivier <lvivier@redhat.com>

> 
> Cc: Laurent Vivier <lvivier@redhat.com>
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>   tcp_vu.c | 21 +++++++++++----------
>   1 file changed, 11 insertions(+), 10 deletions(-)
> 
> diff --git a/tcp_vu.c b/tcp_vu.c
> index 0622f173..6891ed13 100644
> --- a/tcp_vu.c
> +++ b/tcp_vu.c
> @@ -38,7 +38,6 @@
>   static struct iovec iov_vu[VIRTQUEUE_MAX_SIZE + 1];
>   static struct vu_virtq_element elem[VIRTQUEUE_MAX_SIZE];
>   static int head[VIRTQUEUE_MAX_SIZE + 1];
> -static int head_cnt;
>   
>   /**
>    * tcp_vu_hdrlen() - return the size of the header in level 2 frame (TCP)
> @@ -183,7 +182,7 @@ int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags)
>   static ssize_t tcp_vu_sock_recv(const struct ctx *c,
>   				const struct tcp_tap_conn *conn, bool v6,
>   				uint32_t already_sent, size_t fillsize,
> -				int *iov_cnt)
> +				int *iov_cnt, int *head_cnt)
>   {
>   	struct vu_dev *vdev = c->vdev;
>   	struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE];
> @@ -202,7 +201,7 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c,
>   	vu_init_elem(elem, &iov_vu[1], VIRTQUEUE_MAX_SIZE);
>   
>   	elem_cnt = 0;
> -	head_cnt = 0;
> +	*head_cnt = 0;
>   	while (fillsize > 0 && elem_cnt < VIRTQUEUE_MAX_SIZE) {
>   		struct iovec *iov;
>   		size_t frame_size, dlen;
> @@ -221,7 +220,7 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c,
>   		ASSERT(iov->iov_len >= hdrlen);
>   		iov->iov_base = (char *)iov->iov_base + hdrlen;
>   		iov->iov_len -= hdrlen;
> -		head[head_cnt++] = elem_cnt;
> +		head[(*head_cnt)++] = elem_cnt;
>   
>   		fillsize -= dlen;
>   		elem_cnt += cnt;
> @@ -261,17 +260,18 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c,
>   		len -= iov->iov_len;
>   	}
>   	/* adjust head count */
> -	while (head_cnt > 0 && head[head_cnt - 1] >= i)
> -		head_cnt--;
> +	while (*head_cnt > 0 && head[*head_cnt - 1] >= i)
> +		(*head_cnt)--;
> +
>   	/* mark end of array */
> -	head[head_cnt] = i;
> +	head[*head_cnt] = i;
>   	*iov_cnt = i;
>   
>   	/* release unused buffers */
>   	vu_queue_rewind(vq, elem_cnt - i);
>   
>   	/* restore space for headers in iov */
> -	for (i = 0; i < head_cnt; i++) {
> +	for (i = 0; i < *head_cnt; i++) {
>   		struct iovec *iov = &elem[head[i]].in_sg[0];
>   
>   		iov->iov_base = (char *)iov->iov_base - hdrlen;
> @@ -357,11 +357,11 @@ int tcp_vu_data_from_sock(const struct ctx *c, struct tcp_tap_conn *conn)
>   	struct vu_dev *vdev = c->vdev;
>   	struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE];
>   	ssize_t len, previous_dlen;
> +	int i, iov_cnt, head_cnt;
>   	size_t hdrlen, fillsize;
>   	int v6 = CONN_V6(conn);
>   	uint32_t already_sent;
>   	const uint16_t *check;
> -	int i, iov_cnt;
>   
>   	if (!vu_queue_enabled(vq) || !vu_queue_started(vq)) {
>   		debug("Got packet, but RX virtqueue not usable yet");
> @@ -396,7 +396,8 @@ int tcp_vu_data_from_sock(const struct ctx *c, struct tcp_tap_conn *conn)
>   	/* collect the buffers from vhost-user and fill them with the
>   	 * data from the socket
>   	 */
> -	len = tcp_vu_sock_recv(c, conn, v6, already_sent, fillsize, &iov_cnt);
> +	len = tcp_vu_sock_recv(c, conn, v6, already_sent, fillsize,
> +			       &iov_cnt, &head_cnt);
>   	if (len < 0) {
>   		if (len != -EAGAIN && len != -EWOULDBLOCK) {
>   			tcp_rst(c, conn);


  reply	other threads:[~2025-02-18  8:01 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-02-18  2:50 [PATCH] tcp_vu: head_cnt need not be global David Gibson
2025-02-18  8:01 ` Laurent Vivier [this message]
2025-02-18 10:22   ` Stefano Brivio
2025-02-20 10:06   ` David Gibson
2025-02-18 15:30 ` Stefano Brivio

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