block: add fault injection mechanism for faking request timeouts

Only works for the generic request timer handling. Allows one to
sporadically ignore request completions, thus exercising the timeout
handling.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/block/genhd.c b/block/genhd.c
index 8acaff0..4cd3433 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -817,6 +817,11 @@
 static struct device_attribute dev_attr_fail =
 	__ATTR(make-it-fail, S_IRUGO|S_IWUSR, part_fail_show, part_fail_store);
 #endif
+#ifdef CONFIG_FAIL_IO_TIMEOUT
+static struct device_attribute dev_attr_fail_timeout =
+	__ATTR(io-timeout-fail,  S_IRUGO|S_IWUSR, part_timeout_show,
+		part_timeout_store);
+#endif
 
 static struct attribute *disk_attrs[] = {
 	&dev_attr_range.attr,
@@ -829,6 +834,9 @@
 #ifdef CONFIG_FAIL_MAKE_REQUEST
 	&dev_attr_fail.attr,
 #endif
+#ifdef CONFIG_FAIL_IO_TIMEOUT
+	&dev_attr_fail_timeout.attr,
+#endif
 	NULL
 };