log, conf: Add support for logging to file

In some environments, such as KubeVirt pods, we might not have a
system logger available. We could choose to run in foreground, but
this takes away the convenient synchronisation mechanism derived from
forking to background when interfaces are ready.

Add optional logging to file with -l/--log-file and --log-size.

Unfortunately, this means we need to duplicate features that are more
appropriately implemented by a system logger, such as rotation. Keep
that reasonably simple, by using fallocate() with range collapsing
where supported (Linux kernel >= 3.15, extent-based ext4 and XFS) and
falling back to an unsophisticated block-by-block moving of entries
toward the beginning of the file once we reach the (mandatory) size
limit.

While at it, clarify the role of LOG_EMERG in passt.c.

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

1 files changed, 46 insertions, 3 deletions

diff --git a/conf.c b/conf.c
index e9cd4a7..f22940b 100644
--- a/conf.c
+++ b/conf.c
@@ -633,6 +633,9 @@ static void usage(const char *name)
 	info(   "    default: run in background if started from a TTY");
 	info(   "  -e, --stderr		Log to stderr too");
 	info(   "    default: log to system logger only if started from a TTY");
+	info(   "  -l, --log-file PATH	Log (only) to given file");
+	info(   "  --log-size BYTES	Maximum size of log file");
+	info(   "    default: 1 MiB");
 	info(   "  --runas UID|UID:GID 	Run as given UID, GID, which can be");
 	info(   "    numeric, or login and group names");
 	info(   "    default: drop to user \"nobody\"");
@@ -994,6 +997,7 @@ void conf(struct ctx *c, int argc, char **argv)
 		{"quiet",	no_argument,		NULL,		'q' },
 		{"foreground",	no_argument,		NULL,		'f' },
 		{"stderr",	no_argument,		NULL,		'e' },
+		{"log-file",	required_argument,	NULL,		'l' },
 		{"help",	no_argument,		NULL,		'h' },
 		{"socket",	required_argument,	NULL,		's' },
 		{"ns-ifname",	required_argument,	NULL,		'I' },
@@ -1034,26 +1038,28 @@ void conf(struct ctx *c, int argc, char **argv)
 		{"no-netns-quit", no_argument,		NULL,		10 },
 		{"trace",	no_argument,		NULL,		11 },
 		{"runas",	required_argument,	NULL,		12 },
+		{"log-size",	required_argument,	NULL,		13 },
 		{ 0 },
 	};
 	struct get_bound_ports_ns_arg ns_ports_arg = { .c = c };
 	char userns[PATH_MAX] = { 0 }, netns[PATH_MAX] = { 0 };
 	bool v4_only = false, v6_only = false;
+	char *runas = NULL, *logfile = NULL;
 	struct in6_addr *dns6 = c->ip6.dns;
 	struct fqdn *dnss = c->dns_search;
 	uint32_t *dns4 = c->ip4.dns;
 	int name, ret, mask, b, i;
 	const char *optstring;
 	unsigned int ifi = 0;
-	char *runas = NULL;
+	size_t logsize = 0;
 	uid_t uid;
 	gid_t gid;
 
 	if (c->mode == MODE_PASTA) {
 		c->no_dhcp_dns = c->no_dhcp_dns_search = 1;
-		optstring = "dqfehI:p:P:m:a:n:M:g:i:D:S:46t:u:T:U:";
+		optstring = "dqfel:hI:p:P:m:a:n:M:g:i:D:S:46t:u:T:U:";
 	} else {
-		optstring = "dqfehs:p:P:m:a:n:M:g:i:D:S:46t:u:";
+		optstring = "dqfel:hs:p:P:m:a:n:M:g:i:D:S:46t:u:";
 	}
 
 	c->tcp.fwd_in.mode = c->tcp.fwd_out.mode = 0;
@@ -1177,6 +1183,20 @@ void conf(struct ctx *c, int argc, char **argv)
 
 			runas = optarg;
 			break;
+		case 13:
+			if (logsize) {
+				err("Multiple --log-size options given");
+				usage(argv[0]);
+			}
+
+			errno = 0;
+			logsize = strtol(optarg, NULL, 0);
+
+			if (logsize < LOGFILE_SIZE_MIN || errno) {
+				err("Invalid --log-size: %s", optarg);
+				usage(argv[0]);
+			}
+			break;
 		case 'd':
 			if (c->debug) {
 				err("Multiple --debug options given");
@@ -1192,6 +1212,11 @@ void conf(struct ctx *c, int argc, char **argv)
 			c->foreground = 1;
 			break;
 		case 'e':
+			if (logfile) {
+				err("Can't log to both file and stderr");
+				usage(argv[0]);
+			}
+
 			if (c->stderr) {
 				err("Multiple --stderr options given");
 				usage(argv[0]);
@@ -1199,6 +1224,19 @@ void conf(struct ctx *c, int argc, char **argv)
 
 			c->stderr = 1;
 			break;
+		case 'l':
+			if (c->stderr) {
+				err("Can't log to both stderr and file");
+				usage(argv[0]);
+			}
+
+			if (logfile) {
+				err("Multiple --log-file options given");
+				usage(argv[0]);
+			}
+
+			logfile = optarg;
+			break;
 		case 'q':
 			if (c->quiet) {
 				err("Multiple --quiet options given");
@@ -1460,6 +1498,11 @@ void conf(struct ctx *c, int argc, char **argv)
 	if (ret)
 		usage(argv[0]);
 
+	if (logfile) {
+		logfile_init(c->mode == MODE_PASST ? "passt" : "pasta",
+			     logfile, logsize);
+	}
+
 	if (c->mode == MODE_PASTA) {
 		if (conf_pasta_ns(&netns_only, userns, netns,
 				  optind, argc, argv) < 0)