[PATCH] md: Final stages of raid5 expand code

This patch adds raid5_reshape and end_reshape which will start and finish the
reshape processes.

raid5_reshape is only enabled in CONFIG_MD_RAID5_RESHAPE is set, to discourage
accidental use.

Read the 'help' for the CONFIG_MD_RAID5_RESHAPE entry.

and Make sure that you have backups, just in case.

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

3 files changed, 152 insertions, 3 deletions

diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index ac43f98062fd..fd2aae150ccc 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -127,6 +127,32 @@ config MD_RAID5
 
           If unsure, say Y.
 
+config MD_RAID5_RESHAPE
+        bool "Support adding drives to a raid-5 array (experimental)"
+        depends on MD_RAID5 && EXPERIMENTAL
+        ---help---
+          A RAID-5 set can be expanded by adding extra drives. This
+          requires "restriping" the array which means (almost) every
+          block must be written to a different place.
+
+          This option allows such restriping to be done while the array
+          is online.  However it is still EXPERIMENTAL code.  It should
+          work, but please be sure that you have backups.
+
+          You will need a version of mdadm newer than 2.3.1.   During the
+          early stage of reshape there is a critical section where live data
+          is being over-written.  A crash during this time needs extra care
+          for recovery.  The newer mdadm takes a copy of the data in the
+          critical section and will restore it, if necessary, after a crash.
+
+          The mdadm usage is e.g.
+               mdadm --grow /dev/md1 --raid-disks=6
+          to grow '/dev/md1' to having 6 disks.
+
+          Note: The array can only be expanded, not contracted.
+          There should be enough spares already present to make the new
+          array workable.
+
 config MD_RAID6
         tristate "RAID-6 mode"
         depends on BLK_DEV_MD
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 8e65986bc63f..d169bc964676 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -158,11 +158,12 @@ static int start_readonly;
  */
 static DECLARE_WAIT_QUEUE_HEAD(md_event_waiters);
 static atomic_t md_event_count;
-static void md_new_event(mddev_t *mddev)
+void md_new_event(mddev_t *mddev)
 {
         atomic_inc(&md_event_count);
         wake_up(&md_event_waiters);
 }
+EXPORT_SYMBOL_GPL(md_new_event);
 
 /*
  * Enables to iterate over all existing md arrays
@@ -4467,7 +4468,7 @@ static DECLARE_WAIT_QUEUE_HEAD(resync_wait);
 
 #define SYNC_MARKS      10
 #define SYNC_MARK_STEP  (3*HZ)
-static void md_do_sync(mddev_t *mddev)
+void md_do_sync(mddev_t *mddev)
 {
         mddev_t *mddev2;
         unsigned int currspeed = 0,
@@ -4704,6 +4705,7 @@ static void md_do_sync(mddev_t *mddev)
         set_bit(MD_RECOVERY_DONE, &mddev->recovery);
         md_wakeup_thread(mddev->thread);
 }
+EXPORT_SYMBOL_GPL(md_do_sync);
 
 
 /*
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 56cba8d3e398..b29135acb1d9 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -331,6 +331,8 @@ static int grow_stripes(raid5_conf_t *conf, int num)
         }
         return 0;
 }
+
+#ifdef CONFIG_MD_RAID5_RESHAPE
 static int resize_stripes(raid5_conf_t *conf, int newsize)
 {
         /* Make all the stripes able to hold 'newsize' devices.
@@ -451,7 +453,7 @@ static int resize_stripes(raid5_conf_t *conf, int newsize)
         conf->pool_size = newsize;
         return err;
 }
-
+#endif
 
 static int drop_one_stripe(raid5_conf_t *conf)
 {
@@ -1034,6 +1036,8 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, in
         return 0;
 }
 
+static void end_reshape(raid5_conf_t *conf);
+
 static int stripe_to_pdidx(sector_t stripe, raid5_conf_t *conf, int disks)
 {
         int sectors_per_chunk = conf->chunk_size >> 9;
@@ -1844,6 +1848,10 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
         if (sector_nr >= max_sector) {
                 /* just being told to finish up .. nothing much to do */
                 unplug_slaves(mddev);
+                if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery)) {
+                        end_reshape(conf);
+                        return 0;
+                }
 
                 if (mddev->curr_resync < max_sector) /* aborted */
                         bitmap_end_sync(mddev->bitmap, mddev->curr_resync,
@@ -2464,6 +2472,116 @@ static int raid5_resize(mddev_t *mddev, sector_t sectors)
         return 0;
 }
 
+#ifdef CONFIG_MD_RAID5_RESHAPE
+static int raid5_reshape(mddev_t *mddev, int raid_disks)
+{
+        raid5_conf_t *conf = mddev_to_conf(mddev);
+        int err;
+        mdk_rdev_t *rdev;
+        struct list_head *rtmp;
+        int spares = 0;
+        int added_devices = 0;
+
+        if (mddev->degraded ||
+            test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
+                return -EBUSY;
+        if (conf->raid_disks > raid_disks)
+                return -EINVAL; /* Cannot shrink array yet */
+        if (conf->raid_disks == raid_disks)
+                return 0; /* nothing to do */
+
+        /* Can only proceed if there are plenty of stripe_heads.
+         * We need a minimum of one full stripe,, and for sensible progress
+         * it is best to have about 4 times that.
+         * If we require 4 times, then the default 256 4K stripe_heads will
+         * allow for chunk sizes up to 256K, which is probably OK.
+         * If the chunk size is greater, user-space should request more
+         * stripe_heads first.
+         */
+        if ((mddev->chunk_size / STRIPE_SIZE) * 4 > conf->max_nr_stripes) {
+                printk(KERN_WARNING "raid5: reshape: not enough stripes.  Needed %lu\n",
+                       (mddev->chunk_size / STRIPE_SIZE)*4);
+                return -ENOSPC;
+        }
+
+        ITERATE_RDEV(mddev, rdev, rtmp)
+                if (rdev->raid_disk < 0 &&
+                    !test_bit(Faulty, &rdev->flags))
+                        spares++;
+        if (conf->raid_disks + spares < raid_disks-1)
+                /* Not enough devices even to make a degraded array
+                 * of that size
+                 */
+                return -EINVAL;
+
+        err = resize_stripes(conf, raid_disks);
+        if (err)
+                return err;
+
+        spin_lock_irq(&conf->device_lock);
+        conf->previous_raid_disks = conf->raid_disks;
+        mddev->raid_disks = conf->raid_disks = raid_disks;
+        conf->expand_progress = 0;
+        spin_unlock_irq(&conf->device_lock);
+
+        /* Add some new drives, as many as will fit.
+         * We know there are enough to make the newly sized array work.
+         */
+        ITERATE_RDEV(mddev, rdev, rtmp)
+                if (rdev->raid_disk < 0 &&
+                    !test_bit(Faulty, &rdev->flags)) {
+                        if (raid5_add_disk(mddev, rdev)) {
+                                char nm[20];
+                                set_bit(In_sync, &rdev->flags);
+                                conf->working_disks++;
+                                added_devices++;
+                                sprintf(nm, "rd%d", rdev->raid_disk);
+                                sysfs_create_link(&mddev->kobj, &rdev->kobj, nm);
+                        } else
+                                break;
+                }
+
+        mddev->degraded = (raid_disks - conf->previous_raid_disks) - added_devices;
+        clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
+        clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
+        set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
+        set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
+        mddev->sync_thread = md_register_thread(md_do_sync, mddev,
+                                                "%s_reshape");
+        if (!mddev->sync_thread) {
+                mddev->recovery = 0;
+                spin_lock_irq(&conf->device_lock);
+                mddev->raid_disks = conf->raid_disks = conf->previous_raid_disks;
+                conf->expand_progress = MaxSector;
+                spin_unlock_irq(&conf->device_lock);
+                return -EAGAIN;
+        }
+        md_wakeup_thread(mddev->sync_thread);
+        md_new_event(mddev);
+        return 0;
+}
+#endif
+
+static void end_reshape(raid5_conf_t *conf)
+{
+        struct block_device *bdev;
+
+        conf->mddev->array_size = conf->mddev->size * (conf->mddev->raid_disks-1);
+        set_capacity(conf->mddev->gendisk, conf->mddev->array_size << 1);
+        conf->mddev->changed = 1;
+
+        bdev = bdget_disk(conf->mddev->gendisk, 0);
+        if (bdev) {
+                mutex_lock(&bdev->bd_inode->i_mutex);
+                i_size_write(bdev->bd_inode, conf->mddev->array_size << 10);
+                mutex_unlock(&bdev->bd_inode->i_mutex);
+                bdput(bdev);
+        }
+        spin_lock_irq(&conf->device_lock);
+        conf->expand_progress = MaxSector;
+        spin_unlock_irq(&conf->device_lock);
+}
+
 static void raid5_quiesce(mddev_t *mddev, int state)
 {
         raid5_conf_t *conf = mddev_to_conf(mddev);
@@ -2502,6 +2620,9 @@ static struct mdk_personality raid5_personality =
         .spare_active   = raid5_spare_active,
         .sync_request   = sync_request,
         .resize         = raid5_resize,
+#ifdef CONFIG_MD_RAID5_RESHAPE
+        .reshape        = raid5_reshape,
+#endif
         .quiesce        = raid5_quiesce,
 };