From 2bace8b95108746f6123d312f47f5bda4eb17a26 Mon Sep 17 00:00:00 2001
From: Christian Thaeter <ct@pipapo.org>
Date: Sat, 25 Jul 2009 20:55:15 +0200
Subject: [PATCH] trivial: doc: hpfall: reduce risk that hpfall can do harm
Improve the example code to be at least useable, as in not causing
harm (as shown below). Code can still be improved further, but this
adds some basic safeguards.
1. hpfall *MUST* mlockall(MCL_CURRENT|MCL_FUTURE); itself!
Since the Program sits and waits most of the time it becomes very likely
swapped out. If it gets woken up when the laptop drops from the table
while it is swapped out it actually triggers harddrive activity!
2. Daemonize hpfall using 'daemon(0,0)' (quick and dirty).
3. Give hpfall realtime priority.
Should give a chance that it has less latency when woken up.
Signed-off-by: Christian Thaeter <ct@pipapo.org>
Signed-off-by: Frans Pop <elendil@planet.nl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
---
Documentation/hwmon/hpfall.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/Documentation/hwmon/hpfall.c b/Documentation/hwmon/hpfall.c
index d2f6711b468b..a3cfe1a5f964 100644
--- a/Documentation/hwmon/hpfall.c
+++ b/Documentation/hwmon/hpfall.c
@@ -16,6 +16,8 @@
#include <stdint.h>
#include <errno.h>
#include <signal.h>
+#include <sys/mman.h>
+#include <sched.h>
void write_int(char *path, int i)
{
@@ -62,6 +64,7 @@ void ignore_me(void)
int main(int argc, char *argv[])
{
int fd, ret;
+ struct sched_param param;
fd = open("/dev/freefall", O_RDONLY);
if (fd < 0) {
@@ -69,6 +72,11 @@ int main(int argc, char *argv[])
return EXIT_FAILURE;
}
+ daemon(0, 0);
+ param.sched_priority = sched_get_priority_max(SCHED_FIFO);
+ sched_setscheduler(0, SCHED_FIFO, ¶m);
+ mlockall(MCL_CURRENT|MCL_FUTURE);
+
signal(SIGALRM, ignore_me);
for (;;) {
--
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