md: expose the degraded status of an assembled array through sysfs

The 'degraded' attribute is useful to quickly determine if the array is
degraded, instead of parsing 'mdadm -D' output or relying on the other
techniques (number of working devices against number of defined devices,
etc.).  The md code already keeps track of this attribute, so it's useful to
export it.

Signed-off-by: Iustin Pop <iusty@k1024.org>
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 510625e3a965..c059ae6f37e5 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -2833,6 +2833,12 @@ sync_max_store(mddev_t *mddev, const char *buf, size_t len)
 static struct md_sysfs_entry md_sync_max =
 __ATTR(sync_speed_max, S_IRUGO|S_IWUSR, sync_max_show, sync_max_store);
 
+static ssize_t
+degraded_show(mddev_t *mddev, char *page)
+{
+        return sprintf(page, "%d\n", mddev->degraded);
+}
+static struct md_sysfs_entry md_degraded = __ATTR_RO(degraded);
 
 static ssize_t
 sync_speed_show(mddev_t *mddev, char *page)
@@ -2976,6 +2982,7 @@ static struct attribute *md_redundancy_attrs[] = {
         &md_suspend_lo.attr,
         &md_suspend_hi.attr,
         &md_bitmap.attr,
+        &md_degraded.attr,
         NULL,
 };
 static struct attribute_group md_redundancy_group = {