MEDIUM: log: add support for logging to a ring buffer

Now by prefixing a log server with "ring@<name>" it's possible to send
the logs to a ring buffer. One nice thing is that it allows multiple
sessions to consult the logs in real time in parallel over the CLI, and
without requiring file system access. At the moment, ring0 is created as
a default sink for tracing purposes and is available. No option is
provided to create new rings though this is trivial to add to the global
section.

doc/configuration.txt

@@ -933,6 +933,12 @@ log <address> [len <length>] [format <format>] [sample <ranges>:<smp_size>]
         - "stdout" / "stderr", which are respectively aliases for "fd@1" and
           "fd@2", see above.
 
+        - A ring buffer in the form "ring@<name>", which will correspond to an
+          in-memory ring buffer accessible over the CLI using the "show events"
+          command, which will also list existing rings and their sizes. Such
+          buffers are lost on reload or restart but when used as a complement
+          this can help troubleshooting by having the logs instantly available.
+
         You may want to reference some environment variables in the address
         parameter, see section 2.3 about environment variables.
 
@@ -5385,6 +5391,13 @@ no log
                - "stdout" / "stderr", which are respectively aliases for "fd@1"
                  and "fd@2", see above.
 
+               - A ring buffer in the form "ring@<name>", which will correspond
+                 to an in-memory ring buffer accessible over the CLI using the
+                 "show events" command, which will also list existing rings and
+                 their sizes. Such buffers are lost on reload or restart but
+                 when used as a complement this can help troubleshooting by
+                 having the logs instantly available.
+
                You may want to reference some environment variables in the
                address parameter, see section 2.3 about environment variables.
 

include/types/log.h

@@ -28,6 +28,7 @@
 #include <common/config.h>
 #include <common/hathreads.h>
 #include <common/mini-clist.h>
+#include <types/ring.h>
 
 #define NB_LOG_FACILITIES       24
 #define NB_LOG_LEVELS           8
@@ -51,6 +52,7 @@ enum {
 enum log_tgt {
 	LOG_TARGET_DGRAM = 0, // datagram address (udp, unix socket)
 	LOG_TARGET_FD,        // file descriptor
+	LOG_TARGET_BUFFER,    // ring buffer
 };
 
 /* lists of fields that can be logged */
@@ -203,6 +205,7 @@ struct logsrv {
 	struct list list;
 	struct sockaddr_storage addr;
 	struct smp_info lb;
+	struct ring *ring;
 	enum log_tgt type;
 	int format;
 	int facility;

src/log.c

@@ -39,7 +39,9 @@
 #include <proto/fd.h>
 #include <proto/frontend.h>
 #include <proto/log.h>
+#include <proto/ring.h>
 #include <proto/sample.h>
+#include <proto/sink.h>
 #include <proto/ssl_sock.h>
 #include <proto/stream.h>
 #include <proto/stream_interface.h>
@@ -1000,6 +1002,20 @@ int parse_logsrv(char **args, struct list *logsrvs, int do_del, char **err)
 
 	/* now, back to the address */
 	logsrv->type = LOG_TARGET_DGRAM;
+	if (strncmp(args[1], "ring@", 5) == 0) {
+		struct sink *sink = sink_find(args[1] + 5);
+
+		if (!sink || sink->type != SINK_TYPE_BUFFER) {
+			memprintf(err, "cannot find ring buffer '%s'", args[1] + 5);
+			goto error;
+		}
+
+		logsrv->addr.ss_family = AF_UNSPEC;
+		logsrv->type = LOG_TARGET_BUFFER;
+		logsrv->ring = sink->ctx.ring;
+		goto done;
+	}
+
 	if (strncmp(args[1], "fd@", 3) == 0)
 		logsrv->type = LOG_TARGET_FD;
 
@@ -1017,6 +1033,7 @@ int parse_logsrv(char **args, struct list *logsrvs, int do_del, char **err)
 		if (!port1)
 			set_host_port(&logsrv->addr, SYSLOG_PORT);
 	}
+ done:
 	LIST_ADDQ(logsrvs, &logsrv->list);
 	return 1;
 
@@ -1510,12 +1527,15 @@ static inline void __do_send_log(struct logsrv *logsrv, int nblogger, char *pid_
 		/* the socket's address is a file descriptor */
 		plogfd = (int *)&((struct sockaddr_in *)&logsrv->addr)->sin_addr.s_addr;
 	}
+	else if (logsrv->type == LOG_TARGET_BUFFER) {
+		plogfd = NULL;
+	}
 	else if (logsrv->addr.ss_family == AF_UNIX)
 		plogfd = &logfdunix;
 	else
 		plogfd = &logfdinet;
 
-	if (unlikely(*plogfd < 0)) {
+	if (plogfd && unlikely(*plogfd < 0)) {
 		/* socket not successfully initialized yet */
 		if ((*plogfd = socket(logsrv->addr.ss_family, SOCK_DGRAM,
 							  (logsrv->addr.ss_family == AF_UNIX) ? 0 : IPPROTO_UDP)) < 0) {
@@ -1652,7 +1672,7 @@ static inline void __do_send_log(struct logsrv *logsrv, int nblogger, char *pid_
 	max = MIN(size, maxlen - sd_max) - 1;
 send:
 	if (logsrv->addr.ss_family == AF_UNSPEC) {
-		/* the target is a direct file descriptor */
+		/* the target is a file descriptor or a ring buffer */
 		struct ist msg[7];
 
 		msg[0].ptr = hdr_ptr;  msg[0].len = hdr_max;
@@ -1663,7 +1683,10 @@ send:
 		msg[5].ptr = sd;       msg[5].len = sd_max;
 		msg[6].ptr = dataptr;  msg[6].len = max;
 
-		sent = fd_write_frag_line(*plogfd, ~0, NULL, 0, msg, 7, 1);
+		if (logsrv->type == LOG_TARGET_BUFFER)
+			sent = ring_write(logsrv->ring, ~0, NULL, 0, msg, 7);
+		else /* LOG_TARGET_FD */
+			sent = fd_write_frag_line(*plogfd, ~0, NULL, 0, msg, 7, 1);
 	}
 	else {
 		iovec[0].iov_base = hdr_ptr;