[PATCH] md: Support suspending of IO to regions of an md array

This allows user-space to access data safely.  This is needed for raid5
reshape as user-space needs to take a backup of the first few stripes before
allowing reshape to commence.

It will also be useful in cluster-aware raid1 configurations so that all
cluster members can leave a section of the array untouched while a
resync/recovery happens.

A 'start' and 'end' of the suspended range are written to 2 sysfs attributes.
Note that only one range can be suspended at a time.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 355dafb98aac..bb16ac231a40 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -1805,6 +1805,15 @@ static int make_request(request_queue_t *q, struct bio * bi)
                                         goto retry;
                                 }
                         }
+                        /* FIXME what if we get a false positive because these
+                         * are being updated.
+                         */
+                        if (logical_sector >= mddev->suspend_lo &&
+                            logical_sector < mddev->suspend_hi) {
+                                release_stripe(sh);
+                                schedule();
+                                goto retry;
+                        }
 
                         if (test_bit(STRIPE_EXPANDING, &sh->state) ||
                             !add_stripe_bio(sh, bi, dd_idx, (bi->bi_rw&RW_MASK))) {
@@ -2725,6 +2734,10 @@ static void raid5_quiesce(mddev_t *mddev, int state)
         raid5_conf_t *conf = mddev_to_conf(mddev);
 
         switch(state) {
+        case 2: /* resume for a suspend */
+                wake_up(&conf->wait_for_overlap);
+                break;
+
         case 1: /* stop all writes */
                 spin_lock_irq(&conf->device_lock);
                 conf->quiesce = 1;
@@ -2738,6 +2751,7 @@ static void raid5_quiesce(mddev_t *mddev, int state)
                 spin_lock_irq(&conf->device_lock);
                 conf->quiesce = 0;
                 wake_up(&conf->wait_for_stripe);
+                wake_up(&conf->wait_for_overlap);
                 spin_unlock_irq(&conf->device_lock);
                 break;
         }