[PATCH] fault-injection capability for disk IO

This patch provides fault-injection capability for disk IO.

Boot option:

fail_make_request=<probability>,<interval>,<space>,<times>

	<interval> -- specifies the interval of failures.

	<probability> -- specifies how often it should fail in percent.

	<space> -- specifies the size of free space where disk IO can be issued
		   safely in bytes.

	<times> -- specifies how many times failures may happen at most.

Debugfs:

/debug/fail_make_request/interval
/debug/fail_make_request/probability
/debug/fail_make_request/specifies
/debug/fail_make_request/times

Example:

	fail_make_request=10,100,0,-1
	echo 1 > /sys/blocks/hda/hda1/make-it-fail

generic_make_request() on /dev/hda1 fails once per 10 times.

Cc: Jens Axboe <axboe@suse.de>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/partitions/check.c

@@ -276,12 +276,39 @@ static struct part_attribute part_attr_stat = {
 	.show	= part_stat_read
 };
 
+#ifdef CONFIG_FAIL_MAKE_REQUEST
+
+static ssize_t part_fail_store(struct hd_struct * p,
+			       const char *buf, size_t count)
+{
+	int i;
+
+	if (count > 0 && sscanf(buf, "%d", &i) > 0)
+		p->make_it_fail = (i == 0) ? 0 : 1;
+
+	return count;
+}
+static ssize_t part_fail_read(struct hd_struct * p, char *page)
+{
+	return sprintf(page, "%d\n", p->make_it_fail);
+}
+static struct part_attribute part_attr_fail = {
+	.attr = {.name = "make-it-fail", .mode = S_IRUGO | S_IWUSR },
+	.store	= part_fail_store,
+	.show	= part_fail_read
+};
+
+#endif
+
 static struct attribute * default_attrs[] = {
 	&part_attr_uevent.attr,
 	&part_attr_dev.attr,
 	&part_attr_start.attr,
 	&part_attr_size.attr,
 	&part_attr_stat.attr,
+#ifdef CONFIG_FAIL_MAKE_REQUEST
+	&part_attr_fail.attr,
+#endif
 	NULL,
 };