ulogd: use a RT scheduler by default

Is common that ulogd runs in scenarios where a lot of packets are to be logged.
If there are more packets than ulogd can handle, users can start seing log
messages like this:

 ulogd[556]: We are losing events. Please, consider using the clauses \
 `netlink_socket_buffer_size' and `netlink_socket_buffer_maxsize'

Which means that Netlink buffer overrun have happened.
There are several approaches to prevent this situation:

 * in the ruleset, limit the amount of packet queued for log
 * in the ruleset, instruct the kernel to use a queue-threshold
 * from userspace, increment Netlink buffer sizes
 * from userspace, configure ulogd to run as high priority process

The first 3 method can be configured by users at runtime.
This patch deals with the last method. SCHED_RR is configured by default,
with no associated configuration parameter for users, since I believe
this is common enough, and should produce no harm.

A similar approach is used in the conntrackd daemon.

Signed-off-by: Arturo Borrero Gonzalez <arturo@netfilter.org>
Acked-by: Eric Leblond <eric@regit.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 15 insertions, 0 deletions

diff --git a/src/ulogd.c b/src/ulogd.c
index b85d0ee..684444f 100644
--- a/src/ulogd.c
+++ b/src/ulogd.c
@@ -64,6 +64,7 @@
 #include <syslog.h>
 #include <sys/time.h>
 #include <sys/stat.h>
+#include <sched.h>
 #include <ulogd/conffile.h>
 #include <ulogd/ulogd.h>
 #ifdef DEBUG
@@ -1395,6 +1396,19 @@ static void signal_handler_task(int signal)
 	deliver_signal_pluginstances(signal);
 }
 
+static void set_scheduler(void)
+{
+	struct sched_param schedparam;
+	int sched_type;
+
+	schedparam.sched_priority = sched_get_priority_max(SCHED_RR);
+	sched_type = SCHED_RR;
+
+	if (sched_setscheduler(0, sched_type, &schedparam) < 0)
+		fprintf(stderr, "WARNING: scheduler configuration failed:"
+			" %s\n", strerror(errno));
+}
+
 static void print_usage(void)
 {
 	printf("ulogd Version %s\n", VERSION);
@@ -1589,6 +1603,7 @@ int main(int argc, char* argv[])
 	signal(SIGALRM, &signal_handler);
 	signal(SIGUSR1, &signal_handler);
 	signal(SIGUSR2, &signal_handler);
+	set_scheduler();
 
 	ulogd_log(ULOGD_INFO, 
 		  "initialization finished, entering main loop\n");