log: Initialise timestamp for relative log time also if we use a log file

...not just for debug messages. Otherwise, timestamps in the log file
are consistent but the starting point is not zero.

Do this right away as we enter main(), so that the resulting
timestamps are as closely as possible relative to when we start.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

log.c

@@ -40,7 +40,7 @@ static size_t	log_written;		/* Currently used bytes in log file */
 static size_t	log_cut_size;		/* Bytes to cut at start on rotation */
 static char	log_header[BUFSIZ];	/* File header, written back on cuts */
 
-static struct timespec log_start;	/* Start timestamp */
+struct timespec	log_start;		/* Start timestamp */
 
 int		log_trace;		/* --trace mode enabled */
 bool		log_conf_parsed;	/* Logging options already parsed */
@@ -154,8 +154,6 @@ void __openlog(const char *ident, int option, int facility)
 {
 	(void)option;
 
-	clock_gettime(CLOCK_REALTIME, &log_start);
-
 	if (log_sock < 0) {
 		struct sockaddr_un a = { .sun_family = AF_UNIX, };
 

log.h

@@ -44,6 +44,7 @@ void logmsg_perror(int pri, const char *format, ...)
 extern int log_trace;
 extern bool log_conf_parsed;
 extern bool log_runtime;
+extern struct timespec log_start;
 
 void trace_init(int enable);
 #define trace(...)							\

passt.c

@@ -207,6 +207,8 @@ int main(int argc, char **argv)
 	struct timespec now;
 	struct sigaction sa;
 
+	clock_gettime(CLOCK_REALTIME, &log_start);
+
 	arch_avx2_exec(argv);
 
 	isolate_initial();