[PATCH] md: expose device slot information via sysfs

This the role that a device has in an array can be viewed and set.

Signed-off-by: Neil Brown <neilb@suse.de>
Acked-by: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 43 insertions, 0 deletions

diff --git a/Documentation/md.txt b/Documentation/md.txt
index 69f742dee00f..d525fffc873b 100644
--- a/Documentation/md.txt
+++ b/Documentation/md.txt
@@ -236,6 +236,14 @@ Each directory contains:
         providing an ongoing count for arrays with metadata managed by
         userspace.
 
+      slot
+        This gives the role that the device has in the array.  It will
+        either be 'none' if the device is not active in the array
+        (i.e. is a spare or has failed) or an integer less than the
+        'raid_disks' number for the array indicating which possition
+        it currently fills.  This can only be set while assembling an
+        array.  A device for which this is set is assumed to be working.
+
 
 An active md device will also contain and entry for each active device
 in the array.  These are named
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 27a9871f3057..a8169564209d 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1630,10 +1630,45 @@ errors_store(mdk_rdev_t *rdev, const char *buf, size_t len)
 static struct rdev_sysfs_entry rdev_errors =
 __ATTR(errors, 0644, errors_show, errors_store);
 
+static ssize_t
+slot_show(mdk_rdev_t *rdev, char *page)
+{
+        if (rdev->raid_disk < 0)
+                return sprintf(page, "none\n");
+        else
+                return sprintf(page, "%d\n", rdev->raid_disk);
+}
+
+static ssize_t
+slot_store(mdk_rdev_t *rdev, const char *buf, size_t len)
+{
+        char *e;
+        int slot = simple_strtoul(buf, &e, 10);
+        if (strncmp(buf, "none", 4)==0)
+                slot = -1;
+        else if (e==buf || (*e && *e!= '\n'))
+                return -EINVAL;
+        if (rdev->mddev->pers)
+                /* Cannot set slot in active array (yet) */
+                return -EBUSY;
+        if (slot >= rdev->mddev->raid_disks)
+                return -ENOSPC;
+        rdev->raid_disk = slot;
+        /* assume it is working */
+        rdev->flags = 0;
+        set_bit(In_sync, &rdev->flags);
+        return len;
+}
+
+
+static struct rdev_sysfs_entry rdev_slot =
+__ATTR(slot, 0644, slot_show, slot_store);
+
 static struct attribute *rdev_default_attrs[] = {
         &rdev_state.attr,
         &rdev_super.attr,
         &rdev_errors.attr,
+        &rdev_slot.attr,
         NULL,
 };
 static ssize_t