From 3bcdae106e76f3f7259a1e9c251993ec7e33dc96 Mon Sep 17 00:00:00 2001
From: David Lamparter <equinox@opensourcerouting.org>
Date: Sat, 5 Mar 2022 19:43:44 +0100
Subject: [PATCH] lib: add `monitor:<fd>` command line log target

This provides direct raw log output with full metadata directly at
startup regardless of configuration details.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
---
 lib/log_vty.c   | 16 ++++++++++++++++
 lib/zlog_live.c | 16 ++++++++++++----
 lib/zlog_live.h |  1 +
 3 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/lib/log_vty.c b/lib/log_vty.c
index 682c9ea372..ef33a39d4a 100644
--- a/lib/log_vty.c
+++ b/lib/log_vty.c
@@ -427,6 +427,22 @@ void command_setup_early_logging(const char *dest, const char *level)
 		set_log_file(&zt_file_cmdline, NULL, sep, nlevel);
 		return;
 	}
+	if (strcmp(type, "monitor") == 0 && sep) {
+		struct zlog_live_cfg cfg = {};
+		unsigned long fd;
+		char *endp;
+
+		sep++;
+		fd = strtoul(sep, &endp, 10);
+		if (!*sep || *endp) {
+			fprintf(stderr, "invalid monitor fd \"%s\"\n", sep);
+			exit(1);
+		}
+
+		zlog_live_open_fd(&cfg, nlevel, fd);
+		zlog_live_disown(&cfg);
+		return;
+	}
 
 	fprintf(stderr, "invalid log target \"%s\" (\"%s\")\n", type, dest);
 	exit(1);
diff --git a/lib/zlog_live.c b/lib/zlog_live.c
index fd2291a86f..d871e20db1 100644
--- a/lib/zlog_live.c
+++ b/lib/zlog_live.c
@@ -182,8 +182,6 @@ static void zlog_live_sigsafe(struct zlog_target *zt, const char *text,
 void zlog_live_open(struct zlog_live_cfg *cfg, int prio_min, int *other_fd)
 {
 	int sockets[2];
-	struct zlt_live *zte;
-	struct zlog_target *zt;
 
 	if (cfg->target)
 		zlog_live_close(cfg);
@@ -208,13 +206,23 @@ void zlog_live_open(struct zlog_live_cfg *cfg, int prio_min, int *other_fd)
 		shutdown(sockets[0], SHUT_RD);
 
 	*other_fd = sockets[1];
+	zlog_live_open_fd(cfg, prio_min, sockets[0]);
+}
+
+void zlog_live_open_fd(struct zlog_live_cfg *cfg, int prio_min, int fd)
+{
+	struct zlt_live *zte;
+	struct zlog_target *zt;
+
+	if (cfg->target)
+		zlog_live_close(cfg);
 
 	zt = zlog_target_clone(MTYPE_LOG_LIVE, NULL, sizeof(*zte));
 	zte = container_of(zt, struct zlt_live, zt);
 	cfg->target = zte;
 
-	set_nonblocking(sockets[0]);
-	zte->fd = sockets[0];
+	set_nonblocking(fd);
+	zte->fd = fd;
 	zte->zt.prio_min = prio_min;
 	zte->zt.logfn = zlog_live;
 	zte->zt.logfn_sigsafe = zlog_live_sigsafe;
diff --git a/lib/zlog_live.h b/lib/zlog_live.h
index 5e80f016fd..ab8aae452f 100644
--- a/lib/zlog_live.h
+++ b/lib/zlog_live.h
@@ -68,6 +68,7 @@ struct zlog_live_cfg {
 
 extern void zlog_live_open(struct zlog_live_cfg *cfg, int prio_min,
 			   int *other_fd);
+extern void zlog_live_open_fd(struct zlog_live_cfg *cfg, int prio_min, int fd);
 
 static inline bool zlog_live_is_null(struct zlog_live_cfg *cfg)
 {
-- 
2.39.5