Add syslog and fatal signal handler feature

I see random ENOTCONN failures in xfstest generic/013 and generic/014
in my branch, but earliest on the 2nd run - takes ~12hours to get
the issue, but then there are no further information logged.
ENOTCONN points to a daemon crash - I need backtraces and a core dump.

This adds optional handling of fatal signals to print a core dump
and optional syslog logging with these new public functions:

fuse_set_fail_signal_handlers()
    In addition to the existing fuse_set_signal_handlers(). This is not
    enabled together with fuse_set_signal_handlers(), as it is change
    in behavior and file systems might already have their own fatal
    handlers.

fuse_log_enable_syslog
    Print logs to syslog instead of stderr

fuse_log_close_syslog
    Close syslog (for now just does closelog())

Code in fuse_signals.c is also updated, to be an array of signals,
and setting signal handlers is now down with a for-loop instead
of one hand coded set_one_signal_handler() per signal.

1 files changed, 60 insertions, 4 deletions

diff --git a/lib/fuse_log.c b/lib/fuse_log.c
index 0d268ab..95d6379 100644
--- a/lib/fuse_log.c
+++ b/lib/fuse_log.c
@@ -12,12 +12,56 @@
 
 #include <stdarg.h>
 #include <stdio.h>
+#include <stdbool.h>
+#include <syslog.h>
 
-static void default_log_func(
-		__attribute__(( unused )) enum fuse_log_level level,
-		const char *fmt, va_list ap)
+#define MAX_SYSLOG_LINE_LEN 512
+
+static bool to_syslog = false;
+
+static void default_log_func(__attribute__((unused)) enum fuse_log_level level,
+			     const char *fmt, va_list ap)
 {
-	vfprintf(stderr, fmt, ap);
+	if (to_syslog) {
+		int sys_log_level;
+
+		/*
+		 * with glibc fuse_log_level has identical values as
+		 * syslog levels, but we also support BSD - better we convert to
+		 * be sure.
+		 */
+		switch (level) {
+		case FUSE_LOG_DEBUG:
+			sys_log_level = LOG_DEBUG;
+			break;
+		case FUSE_LOG_INFO:
+			sys_log_level = LOG_INFO;
+			break;
+		case FUSE_LOG_NOTICE:
+			sys_log_level = LOG_NOTICE;
+			break;
+		case FUSE_LOG_WARNING:
+			sys_log_level = LOG_WARNING;
+			break;
+		case FUSE_LOG_ERR:
+			sys_log_level = LOG_ERR;
+			break;
+		case FUSE_LOG_CRIT:
+			sys_log_level = LOG_CRIT;
+			break;
+		case FUSE_LOG_ALERT:
+			sys_log_level = LOG_ALERT;
+			break;
+		case FUSE_LOG_EMERG:
+			sys_log_level = LOG_EMERG;
+		}
+
+		char log[MAX_SYSLOG_LINE_LEN];
+		vsnprintf(log, MAX_SYSLOG_LINE_LEN, fmt, ap);
+		syslog(sys_log_level, "%s", log);
+	} else {
+		vfprintf(stderr, fmt, ap);
+	}
 }
 
 static fuse_log_func_t log_func = default_log_func;
@@ -38,3 +82,15 @@ void fuse_log(enum fuse_log_level level, const char *fmt, ...)
 	log_func(level, fmt, ap);
 	va_end(ap);
 }
+
+void fuse_log_enable_syslog(const char *ident, int option, int facility)
+{
+	to_syslog = true;
+
+	openlog(ident, option, facility);
+}
+
+void fuse_log_close_syslog(void)
+{
+	closelog();
+}
\ No newline at end of file