On Sat, Nov 27, 2021 at 04:19:26PM +0100, mwilck@xxxxxxxx wrote:
> From: Martin Wilck <mwilck@xxxxxxxx>
>
> send_packet() may busy-loop. By polling for POLLOUT, we can
> avoid that, even if it's very unlikely in practice.
>
> Signed-off-by: Martin Wilck <mwilck@xxxxxxxx>
Reviewed-by: Benjamin Marzinski <bmarzins@xxxxxxxxxx>
> ---
> multipathd/uxlsnr.c | 41 ++++++++++++++++++++++++++++++-----------
> 1 file changed, 30 insertions(+), 11 deletions(-)
>
> diff --git a/multipathd/uxlsnr.c b/multipathd/uxlsnr.c
> index 1ebcf10..c5da569 100644
> --- a/multipathd/uxlsnr.c
> +++ b/multipathd/uxlsnr.c
> @@ -447,7 +447,6 @@ static int client_state_machine(struct client *c, struct vectors *vecs,
> short revents)
> {
> ssize_t n;
> - const char *buf;
>
> condlog(4, "%s: cli[%d] poll=%x state=%d cmd=\"%s\" repl \"%s\"", __func__,
> c->fd, revents, c->state, c->cmd, get_strbuf_str(&c->reply));
> @@ -527,7 +526,8 @@ static int client_state_machine(struct client *c, struct vectors *vecs,
> free_keys(c->cmdvec);
> c->cmdvec = NULL;
> set_client_state(c, CLT_SEND);
> - return STM_CONT;
> + /* Wait for POLLOUT */
> + return STM_BREAK;
> } else {
> condlog(4, "%s: cli[%d] waiting for lock", __func__, c->fd);
> return STM_BREAK;
> @@ -538,22 +538,38 @@ static int client_state_machine(struct client *c, struct vectors *vecs,
> free_keys(c->cmdvec);
> c->cmdvec = NULL;
> set_client_state(c, CLT_SEND);
> - return STM_CONT;
> + /* Wait for POLLOUT */
> + return STM_BREAK;
>
> case CLT_SEND:
> if (get_strbuf_len(&c->reply) == 0)
> default_reply(c, c->error);
>
> - buf = get_strbuf_str(&c->reply);
> + if (c->cmd_len == 0) {
> + size_t len = get_strbuf_len(&c->reply) + 1;
>
> - if (send_packet(c->fd, buf) != 0)
> - dead_client(c);
> - else
> - condlog(4, "cli[%d]: Reply [%zu bytes]", c->fd,
> - get_strbuf_len(&c->reply) + 1);
> - reset_strbuf(&c->reply);
> + if (send(c->fd, &len, sizeof(len), MSG_NOSIGNAL)
> + != sizeof(len))
> + c->error = -ECONNRESET;
> + c->cmd_len = len;
> + return STM_BREAK;
> + }
>
> - set_client_state(c, CLT_RECV);
> + if (c->len < c->cmd_len) {
> + const char *buf = get_strbuf_str(&c->reply);
> +
> + n = send(c->fd, buf + c->len, c->cmd_len, MSG_NOSIGNAL);
> + if (n == -1) {
> + if (!(errno == EAGAIN || errno == EINTR))
> + c->error = -ECONNRESET;
> + } else
> + c->len += n;
> + }
> +
> + if (c->len >= c->cmd_len) {
> + condlog(4, "cli[%d]: Reply [%zu bytes]", c->fd, c->cmd_len);
> + set_client_state(c, CLT_RECV);
> + }
> return STM_BREAK;
>
> default:
> @@ -687,6 +703,9 @@ void *uxsock_listen(long ux_sock, void *trigger_data)
> case CLT_RECV:
> polls[i].events = POLLIN;
> break;
> + case CLT_SEND:
> + polls[i].events = POLLOUT;
> + break;
> default:
> /* don't poll for this client */
> continue;
> --
> 2.33.1
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