Close idle logfiles

We hit the maximum file limit.  75% of that seems to be from active
machines, but we may also have stale ones that we needlessly keep open.
It is fairly cheap to close them once an hour.

Signed-off-by: Joern Engel <joern@logfs.org>

1 files changed, 28 insertions, 10 deletions

diff --git a/cancd.c b/cancd.c
index dd7e0f2..96f7182 100644
--- a/cancd.c
+++ b/cancd.c
@@ -441,6 +441,25 @@ uint64_t gethrtime(void)
 	return tod.tv_sec * 1000000000ULL + tod.tv_nsec;
 }
 
+static void close_logfile(struct source_ip *sip)
+{
+	int fd;
+
+	/*
+	 * We cache the open fd for 60s.  We also cache the filesize.
+	 * This reduces cpu overhead a bit, but means logrotate has to
+	 * keep the file around for 60s after rotation and we can
+	 * overshoot the size limit a bit.
+	 */
+	do {
+		if (sip->fd < 0 || gethrtime() < sip->reopen_time)
+			return;
+		fd = sip->fd;
+	} while (!__sync_bool_compare_and_swap(&sip->fd, fd, -1));
+
+	close(fd);
+}
+
 static void do_output(char *buf, int len, struct sockaddr_in *addr, socklen_t socklen)
 {
 	int err;
@@ -452,16 +471,7 @@ static void do_output(char *buf, int len, struct sockaddr_in *addr, socklen_t so
 	if (!name)
 		return;
 
-	/*
-	 * We cache the open fd for 60s.  We also cache the filesize.
-	 * This reduces cpu overhead a bit, but means logrotate has to
-	 * keep the file around for 60s after rotation and we can
-	 * overshoot the size limit a bit.
-	 */
-	if (sip->fd >= 0 && gethrtime() > sip->reopen_time) {
-		close(sip->fd);
-		sip->fd = -1;
-	}
+	close_logfile(sip);
 
 	if (sip->fd < 0) {
 		sip->fd = open(name, O_WRONLY | O_APPEND | O_CREAT, 0644);
@@ -734,6 +744,14 @@ static void dns_visitor(void *_sip, long unused, u32 ip, size_t unused2)
 	const char *old;
 	char *new, *c;
 
+	/*
+	 * Close idle logfiles.  Maybe the machine no longer exists,
+	 * maybe it was renamed, maybe it has gone quiet for an hour.
+	 * Either way, it no longer saves resources to keep the file
+	 * open.
+	 */
+	close_logfile(sip);
+
 	he = gethostbyaddr(&ip, 4, AF_INET);
 	if (!he)
 		return;