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);
next prev parent 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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=53e1b351-da19-4491-b438-1e77e0dc836c@redhat.com \
--to=lvivier@redhat.com \
--cc=david@gibson.dropbear.id.au \
--cc=passt-dev@passt.top \
--cc=sbrivio@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://passt.top/passt
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for IMAP folder(s).