usyslogd: more control over log rotate behaviour, command line processing

- Add more fine grained control over how log rotation is supposed to behave
 - Add command line option processing to usyslogd
 - Expose log rotation control via command line switches
 - Add default values to usyslogd service for pygos use case

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>

services/usyslogd

@@ -1,5 +1,5 @@
 description "starting usyslogd"
-exec usyslogd
+exec usyslogd --rotate-replace --max-size 8192
 type respawn limit 5
 target boot
 after vfs

syslogd/backend.h

@@ -20,8 +20,30 @@
 
 #include "proto.h"
 
+enum {
+	/*
+	  Rotate log data in a way that we still generate a continuous stream
+	  of log data. E.g. in the case of log files, move the current log file
+	  to one suffixed with a timestamp. We don't lose any log data.
+	 */
+	LOG_ROTATE_CONTINUOUS = 0x00,
+
+	/*
+	  Rotate log data by overwriting old data with more recent data.
+	  E.g. in the case of log files, move the current log file to one
+	  with a constant prefix, overwriting any existing data.
+	 */
+	LOG_ROTATE_OVERWRITE = 0x01,
+
+	/*
+	  Automatically do a log rotatation if a log stream reaches a preset
+	  size limit.
+	 */
+	LOG_ROTATE_SIZE_LIMIT = 0x10,
+};
+
 typedef struct log_backend_t {
-	int (*init)(struct log_backend_t *log);
+	int (*init)(struct log_backend_t *log, int flags, size_t sizelimit);
 
 	void (*cleanup)(struct log_backend_t *log);
 

syslogd/logfile.c

@@ -83,6 +83,8 @@ typedef struct logfile_t {
 typedef struct {
 	log_backend_t base;
 	logfile_t *list;
+	size_t maxsize;
+	int flags;
 } log_backend_file_t;
 
 
@@ -156,16 +158,20 @@ static int logfile_write(logfile_t *file, const syslog_msg_t *msg)
 	return 0;
 }
 
-static int logfile_rotate(logfile_t *f)
+static int logfile_rotate(logfile_t *f, int flags)
 {
 	char timebuf[32];
 	char *filename;
 	struct tm tm;
 	time_t now;
 
+	if (flags & LOG_ROTATE_OVERWRITE) {
+		strcpy(timebuf, "1");
+	} else {
 		now = time(NULL);
 		gmtime_r(&now, &tm);
 		strftime(timebuf, sizeof(timebuf), "%FT%T", &tm);
+	}
 
 	filename = alloca(strlen(f->filename) + strlen(timebuf) + 2);
 	sprintf(filename, "%s.%s", f->filename, timebuf);
@@ -182,9 +188,10 @@ static int logfile_rotate(logfile_t *f)
 
 /*****************************************************************************/
 
-static int file_backend_init(log_backend_t *log)
+static int file_backend_init(log_backend_t *backend, int flags,
+			     size_t sizelimit)
 {
-	(void)log;
+	log_backend_file_t *log = (log_backend_file_t *)backend;
 
 	if (mkdir(SYSLOG_PATH, 0755)) {
 		if (errno != EEXIST) {
@@ -198,6 +205,8 @@ static int file_backend_init(log_backend_t *log)
 		return -1;
 	}
 
+	log->flags = flags;
+	log->maxsize = sizelimit;
 	return 0;
 }
 
@@ -254,7 +263,13 @@ static int file_backend_write(log_backend_t *backend, const syslog_msg_t *msg)
 		log->list = f;
 	}
 
-	return logfile_write(f, msg);
+	if (logfile_write(f, msg))
+		return -1;
+
+	if ((log->flags & LOG_ROTATE_SIZE_LIMIT) && f->size >= log->maxsize)
+		logfile_rotate(f, log->flags);
+
+	return 0;
 }
 
 static void file_backend_rotate(log_backend_t *backend)
@@ -263,7 +278,7 @@ static void file_backend_rotate(log_backend_t *backend)
 	logfile_t *f;
 
 	for (f = log->list; f != NULL; f = f->next)
-		logfile_rotate(f);
+		logfile_rotate(f, log->flags);
 }
 
 log_backend_file_t filebackend = {

syslogd/main.c

@@ -22,6 +22,7 @@
 #include <stdlib.h>
 #include <signal.h>
 #include <string.h>
+#include <getopt.h>
 #include <errno.h>
 #include <stdio.h>
 
@@ -32,9 +33,41 @@
 
 #define SYSLOG_SOCKET "/dev/log"
 
+#define GPL_URL "https://gnu.org/licenses/gpl.html"
+
+
+static const struct option long_opts[] = {
+	{ "help", no_argument, NULL, 'h' },
+	{ "version", no_argument, NULL, 'V' },
+	{ "rotate-replace", no_argument, NULL, 'r' },
+	{ "max-size", required_argument, NULL, 'm' },
+	{ NULL, 0, NULL, 0 },
+};
+
+const char *short_opts = "hVrm:";
+
+const char *version_string =
+"usyslogd (pygos init) " PACKAGE_VERSION "\n"
+"Copyright (C) 2018 David Oberhollenzer\n\n"
+"License GPLv3+: GNU GPL version 3 or later <" GPL_URL ">.\n"
+"This is free software: you are free to change and redistribute it.\n"
+"There is NO WARRANTY, to the extent permitted by law.\n";
+
+const char *usage_string =
+"Usage: usyslogd [OPTIONS..]\n\n"
+"The following options are supported:\n"
+"  -h, --help             Print this help text and exit\n"
+"  -V, --version          Print version information and exit\n"
+"  -r, --rotate-replace   Replace old log files when doing log rotation.\n"
+"  -m, --max-size <size>  Automatically rotate log files bigger than this.\n";
+
+
 
 static volatile sig_atomic_t syslog_run = 1;
 static volatile sig_atomic_t syslog_rotate = 0;
+static int log_flags = 0;
+static size_t max_size = 0;
+
 
 
 static void sighandler(int signo)
@@ -82,17 +115,58 @@ static int handle_data(int fd)
 	return logmgr->write(logmgr, &msg);
 }
 
-int main(void)
+static void process_options(int argc, char **argv)
+{
+	char *end;
+	int i;
+
+	for (;;) {
+		i = getopt_long(argc, argv, short_opts, long_opts, NULL);
+		if (i == -1)
+			break;
+
+		switch (i) {
+		case 'r':
+			log_flags |= LOG_ROTATE_OVERWRITE;
+			break;
+		case 'm':
+			log_flags |= LOG_ROTATE_SIZE_LIMIT;
+			max_size = strtol(optarg, &end, 10);
+			if (max_size == 0 || *end != '\0') {
+				fputs("Numeric argument > 0 expected for -m\n",
+				      stderr);
+				goto fail;
+			}
+			break;
+		case 'h':
+			fputs(usage_string, stdout);
+			exit(EXIT_SUCCESS);
+		case 'V':
+			fputs(version_string, stdout);
+			exit(EXIT_SUCCESS);
+		default:
+			goto fail;
+		}
+	}
+	return;
+fail:
+	fputs("Try `usyslogd --help' for more information\n", stderr);
+	exit(EXIT_FAILURE);
+}
+
+int main(int argc, char **argv)
 {
 	int sfd, status = EXIT_FAILURE;
 
+	process_options(argc, argv);
+
 	signal_setup();
 
 	sfd = mksock(SYSLOG_SOCKET, SOCK_FLAG_EVERYONE | SOCK_FLAG_DGRAM);
 	if (sfd < 0)
 		return EXIT_FAILURE;
 
-	if (logmgr->init(logmgr))
+	if (logmgr->init(logmgr, log_flags, max_size))
 		goto out;
 
 	while (syslog_run) {