Re: [dm-devel] [PATCH 24/35] multipathd: uxlsnr: use main poll loop for receiving

[Benjamin Marzinski <bmarzins@redhat.com>]

On Fri, Sep 10, 2021 at 01:41:09PM +0200, mwilck@suse.com wrote:
> From: Martin Wilck <mwilck@suse.com>
> 
> As a first step towards our state machine, avoid the call to
> read_all() via recv_packet_from_client(). handle_client() is now
> invoked twice for the same connection. The first time it reads
> the command length, and later on it reads the command itself
> piece-wise, as sent by the client. This will be just a single
> read in most cases, but not always.
> 
Reviewed-by: Benjamin Marzinski <bmarzins@redhat.com>
> Signed-off-by: Martin Wilck <mwilck@suse.com>
> ---
>  multipathd/uxlsnr.c | 90 +++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 75 insertions(+), 15 deletions(-)
> 
> diff --git a/multipathd/uxlsnr.c b/multipathd/uxlsnr.c
> index 2fb23c8..eff4f7b 100644
> --- a/multipathd/uxlsnr.c
> +++ b/multipathd/uxlsnr.c
> @@ -292,6 +292,8 @@ static void handle_inotify(int fd, struct watch_descriptors *wds)
>  		condlog(1, "Multipath configuration updated.\nReload multipathd for changes to take effect");
>  }
>  
> +static const struct timespec ts_zero = { .tv_sec = 0, };
> +
>  static int parse_cmd (char *cmd, char **reply, int *len, void *data,
>  		      int timeout)
>  {
> @@ -394,23 +396,78 @@ static int uxsock_trigger(char *str, char **reply, int *len,
>  	return r;
>  }
>  
> +static void set_client_state(struct client *c, int state)
> +{
> +	switch(state)
> +	{
> +	case CLT_RECV:
> +		reset_strbuf(&c->reply);
> +		memset(c->cmd, '\0', sizeof(c->cmd));
> +		c->expires = ts_zero;
> +		/* fallthrough */
> +	case CLT_SEND:
> +		/* reuse these fields for next data transfer */
> +		c->len = c->cmd_len = 0;
> +		break;
> +	default:
> +		break;
> +	}
> +	c->state = state;
> +}
> +
>  static void handle_client(struct client *c, void *trigger_data)
>  {
>  	int rlen;
> -	char *inbuf, *reply;
> +	char *reply;
> +	ssize_t n;
>  
> -	if (recv_packet_from_client(c->fd, &inbuf, uxsock_timeout) != 0) {
> -		dead_client(c);
> -		return;
> +	switch (c->state) {
> +	case CLT_RECV:
> +		if (c->cmd_len == 0) {
> +			/*
> +			 * We got POLLIN; assume that at least the length can
> +			 * be read immediately.
> +			 */
> +			get_monotonic_time(&c->expires);
> +			c->expires.tv_sec += uxsock_timeout / 1000;
> +			c->expires.tv_nsec += (uxsock_timeout % 1000) * 1000000;
> +			normalize_timespec(&c->expires);
> +			n = mpath_recv_reply_len(c->fd, 0);
> +			if (n == -1) {
> +				condlog(1, "%s: cli[%d]: failed to receive reply len",
> +					__func__, c->fd);
> +				c->error = -ECONNRESET;
> +			} else if (n > _MAX_CMD_LEN) {
> +				condlog(1, "%s: cli[%d]: overlong command (%zd bytes)",
> +					__func__, c->fd, n);
> +				c->error = -ECONNRESET;
> +			} else {
> +				c->cmd_len = n;
> +				condlog(4, "%s: cli[%d]: connected", __func__, c->fd);
> +			}
> +			/* poll for data */
> +			return;
> +		} else if (c->len < c->cmd_len) {
> +			n = recv(c->fd, c->cmd + c->len, c->cmd_len - c->len, 0);
> +			if (n <= 0 && errno != EINTR && errno != EAGAIN) {
> +				condlog(1, "%s: cli[%d]: error in recv: %m",
> +					__func__, c->fd);
> +				c->error = -ECONNRESET;
> +				return;
> +			}
> +			c->len += n;
> +			if (c->len < c->cmd_len)
> +				/* continue polling */
> +				return;
> +			set_client_state(c, CLT_PARSE);
> +		}
> +		break;
> +	default:
> +		break;
>  	}
>  
> -	if (!inbuf) {
> -		condlog(4, "recv_packet_from_client get null request");
> -		return;
> -	}
> -
> -	condlog(4, "cli[%d]: Got request [%s]", c->fd, inbuf);
> -	uxsock_trigger(inbuf, &reply, &rlen,
> +	condlog(4, "cli[%d]: Got request [%s]", c->fd, c->cmd);
> +	uxsock_trigger(c->cmd, &reply, &rlen,
>  		       _socket_client_is_root(c->fd),
>  		       trigger_data);
>  
> @@ -418,11 +475,12 @@ static void handle_client(struct client *c, void *trigger_data)
>  		if (send_packet(c->fd, reply) != 0)
>  			dead_client(c);
>  		else
> -			condlog(4, "cli[%d]: Reply [%d bytes]", c->fd, rlen);
> -		FREE(reply);
> -		reply = NULL;
> +			condlog(4, "cli[%d]: Reply [%zu bytes]", c->fd,
> +				get_strbuf_len(&c->reply) + 1);
> +		reset_strbuf(&c->reply);
>  	}
> -	FREE(inbuf);
> +
> +	set_client_state(c, CLT_RECV);
>  }
>  
>  /*
> @@ -553,6 +611,8 @@ void *uxsock_listen(long ux_sock, void *trigger_data)
>  					continue;
>  				}
>  				handle_client(c, trigger_data);
> +				if (c->error == -ECONNRESET)
> +					dead_client(c);
>  			}
>  		}
>  		/* see if we got a non-fatal signal */
> -- 
> 2.33.0

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