[PATCH 2.6.25-4] getdelays.c: signal handling for log rotation

[Scott Wiersdorf <scott@perlcode.org>]

This adds a USR1 signal handler to getdelays.c, which causes getdelays
to close its logfile and reopen it (if '-w logfile' is
specified). This is useful in situations when getdelays is running for
a long time (i.e, the log file growing) and you need to rotate the
logs but don't want to lose any log data.

Signed-off-by: Scott Wiersdorf <scott@perlcode.org>
---
--- Documentation/accounting/getdelays.c	2008-05-15 09:00:12.000000000 -0600
+++ Documentation/accounting/getdelays.c	2008-06-05 02:23:57.000000000 -0600
@@ -50,6 +50,7 @@ int dbg;
 int print_delays;
 int print_io_accounting;
 int print_task_context_switch_counts;
+volatile sig_atomic_t reopen_log = 0;
 __u64 stime, utime;
 
 #define PRINTF(fmt, arg...) {			\
@@ -80,6 +81,7 @@ static void usage(void)
 	fprintf(stderr, "  -l: listen forever\n");
 	fprintf(stderr, "  -v: debug on\n");
 	fprintf(stderr, "  -C: container path\n");
+	fprintf(stderr, "\nSend USR1 to reopen the logfile if -w is used.\n");
 }
 
 /*
@@ -231,6 +233,30 @@ void print_ioacct(struct taskstats *t)
 		(unsigned long long)t->cancelled_write_bytes);
 }
 
+void catch_usr1(int sig)
+{
+	reopen_log = 1;
+	signal(sig, catch_usr1);
+}
+
+int reopen_logfile(int fd, char *logfile)
+{
+	if (fd) {
+		PRINTF("USR1 received. Closing logfile.\n");
+		close(fd);
+	}
+	fd = open(logfile, O_WRONLY | O_CREAT | O_TRUNC,
+		  S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
+	if (fd == -1) {
+		perror("Cannot open output file\n");
+		exit(1);
+	}
+
+	reopen_log = 0;
+
+	return fd;
+}
+
 int main(int argc, char *argv[])
 {
 	int c, rc, rep_len, aggr_len, len2, cmd_type;
@@ -320,12 +346,8 @@ int main(int argc, char *argv[])
 	}
 
 	if (write_file) {
-		fd = open(logfile, O_WRONLY | O_CREAT | O_TRUNC,
-			  S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
-		if (fd == -1) {
-			perror("Cannot open output file\n");
-			exit(1);
-		}
+		fd = reopen_logfile(fd, logfile);
+		signal(SIGUSR1, catch_usr1); /* only set when write_file is set */
 	}
 
 	if ((nl_sd = create_nl_socket(NETLINK_GENERIC)) < 0)
@@ -444,6 +466,9 @@ int main(int argc, char *argv[])
 								err(1,"write error\n");
 							}
 						}
+						if (reopen_log) {
+							fd = reopen_logfile(fd, logfile);
+						}
 						if (!loop)
 							goto done;
 						break;