[PATCH v4 1/9] log to stderr until process is daemonized, even if a log file is set

[Laine Stump <laine@redhat.com>]

Once a log file (specified on the commandline) is opened, the logging
functions will stop sending error logs to stderr, which is annoying if
passt has been started by another process that wants to collect error
messages from stderr so it can report why passt failed to start. It
would be much nicer if passt continued sending all log messages to
stderr until it daemonizes itself (at which point the process that
started passt can assume that it was started successfully).

The system log mask is set to LOG_EMERG when the process starts, and
we're already using that to do "special" logging during the period
from process start until the log level requested on the commandline is
processed (setting the log mask to something else). This period
*almost* matches with "the time before the process is daemonized"; if
we just delay setting the log mask a tiny bit, then it will match
exactly, and we can use it to determine if we need to send log
messages to stderr even when a log file has been specified and opened.

This patch delays the setting of the log mask until immediately before
the call to __daemon(). It also modifies logfn() slightly, so that it
will log to stderr any time log mask is LOG_EMERG, even if a log file
has been opened.

Signed-off-by: Laine Stump <laine@redhat.com>
---
 log.c   |  4 ++--
 passt.c | 17 ++++++++++-------
 2 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/log.c b/log.c
index 468c730..6dc6673 100644
--- a/log.c
+++ b/log.c
@@ -66,8 +66,8 @@ void name(const char *format, ...) {					\
 		va_end(args);						\
 	}								\
 									\
-	if ((setlogmask(0) & LOG_MASK(LOG_DEBUG) ||			\
-	     setlogmask(0) == LOG_MASK(LOG_EMERG)) && log_file == -1) {	\
+	if ((setlogmask(0) & LOG_MASK(LOG_DEBUG) && log_file == -1) ||	\
+	     setlogmask(0) == LOG_MASK(LOG_EMERG)) {			\
 		va_start(args, format);					\
 		(void)vfprintf(stderr, format, args); 			\
 		va_end(args);						\
diff --git a/passt.c b/passt.c
index d957e14..c48c2d5 100644
--- a/passt.c
+++ b/passt.c
@@ -246,13 +246,6 @@ int main(int argc, char **argv)
 	if (c.stderr || isatty(fileno(stdout)))
 		__openlog(log_name, LOG_PERROR, LOG_DAEMON);
 
-	if (c.debug)
-		__setlogmask(LOG_UPTO(LOG_DEBUG));
-	else if (c.quiet)
-		__setlogmask(LOG_UPTO(LOG_ERR));
-	else
-		__setlogmask(LOG_UPTO(LOG_INFO));
-
 	quit_fd = pasta_netns_quit_init(&c);
 
 	tap_sock_init(&c);
@@ -296,6 +289,16 @@ int main(int argc, char **argv)
 		exit(EXIT_FAILURE);
 	}
 
+	/* Once the log mask is not LOG_EMERG, we will no longer
+	 * log to stderr if there was a log file specified.
+	 */
+	if (c.debug)
+		__setlogmask(LOG_UPTO(LOG_DEBUG));
+	else if (c.quiet)
+		__setlogmask(LOG_UPTO(LOG_ERR));
+	else
+		__setlogmask(LOG_UPTO(LOG_INFO));
+
 	if (!c.foreground)
 		__daemon(pidfile_fd, devnull_fd);
 	else
-- 
@@ -246,13 +246,6 @@ int main(int argc, char **argv)
 	if (c.stderr || isatty(fileno(stdout)))
 		__openlog(log_name, LOG_PERROR, LOG_DAEMON);
 
-	if (c.debug)
-		__setlogmask(LOG_UPTO(LOG_DEBUG));
-	else if (c.quiet)
-		__setlogmask(LOG_UPTO(LOG_ERR));
-	else
-		__setlogmask(LOG_UPTO(LOG_INFO));
-
 	quit_fd = pasta_netns_quit_init(&c);
 
 	tap_sock_init(&c);
@@ -296,6 +289,16 @@ int main(int argc, char **argv)
 		exit(EXIT_FAILURE);
 	}
 
+	/* Once the log mask is not LOG_EMERG, we will no longer
+	 * log to stderr if there was a log file specified.
+	 */
+	if (c.debug)
+		__setlogmask(LOG_UPTO(LOG_DEBUG));
+	else if (c.quiet)
+		__setlogmask(LOG_UPTO(LOG_ERR));
+	else
+		__setlogmask(LOG_UPTO(LOG_INFO));
+
 	if (!c.foreground)
 		__daemon(pidfile_fd, devnull_fd);
 	else
-- 
2.39.1