md: add ->takeover method to support changing the personality managing an array

Implement this for RAID6 to be able to 'takeover' a RAID5 array.  The
new RAID6 will use a layout which places Q on the last device, and
that device will be missing.
If there are any available spares, one will immediately have Q
recovered onto it.

Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 92 insertions, 9 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 6cb31f8da14c..05b613b5e4b2 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -2649,18 +2649,101 @@ level_show(mddev_t *mddev, char *page)
 static ssize_t
 level_store(mddev_t *mddev, const char *buf, size_t len)
 {
+        char level[16];
         ssize_t rv = len;
-        if (mddev->pers)
+        struct mdk_personality *pers;
+        void *priv;
+
+        if (mddev->pers == NULL) {
+                if (len == 0)
+                        return 0;
+                if (len >= sizeof(mddev->clevel))
+                        return -ENOSPC;
+                strncpy(mddev->clevel, buf, len);
+                if (mddev->clevel[len-1] == '\n')
+                        len--;
+                mddev->clevel[len] = 0;
+                mddev->level = LEVEL_NONE;
+                return rv;
+        }
+
+        /* request to change the personality.  Need to ensure:
+         *  - array is not engaged in resync/recovery/reshape
+         *  - old personality can be suspended
+         *  - new personality will access other array.
+         */
+
+        if (mddev->sync_thread || mddev->reshape_position != MaxSector)
                 return -EBUSY;
-        if (len == 0)
-                return 0;
-        if (len >= sizeof(mddev->clevel))
-                return -ENOSPC;
-        strncpy(mddev->clevel, buf, len);
-        if (mddev->clevel[len-1] == '\n')
+
+        if (!mddev->pers->quiesce) {
+                printk(KERN_WARNING "md: %s: %s does not support online personality change\n",
+                       mdname(mddev), mddev->pers->name);
+                return -EINVAL;
+        }
+
+        /* Now find the new personality */
+        if (len == 0 || len >= sizeof(level))
+                return -EINVAL;
+        strncpy(level, buf, len);
+        if (level[len-1] == '\n')
                 len--;
-        mddev->clevel[len] = 0;
-        mddev->level = LEVEL_NONE;
+        level[len] = 0;
+
+        request_module("md-%s", level);
+        spin_lock(&pers_lock);
+        pers = find_pers(LEVEL_NONE, level);
+        if (!pers || !try_module_get(pers->owner)) {
+                spin_unlock(&pers_lock);
+                printk(KERN_WARNING "md: personality %s not loaded\n", level);
+                return -EINVAL;
+        }
+        spin_unlock(&pers_lock);
+
+        if (pers == mddev->pers) {
+                /* Nothing to do! */
+                module_put(pers->owner);
+                return rv;
+        }
+        if (!pers->takeover) {
+                module_put(pers->owner);
+                printk(KERN_WARNING "md: %s: %s does not support personality takeover\n",
+                       mdname(mddev), level);
+                return -EINVAL;
+        }
+
+        /* ->takeover must set new_* and/or delta_disks
+         * if it succeeds, and may set them when it fails.
+         */
+        priv = pers->takeover(mddev);
+        if (IS_ERR(priv)) {
+                mddev->new_level = mddev->level;
+                mddev->new_layout = mddev->layout;
+                mddev->new_chunk = mddev->chunk_size;
+                mddev->raid_disks -= mddev->delta_disks;
+                mddev->delta_disks = 0;
+                module_put(pers->owner);
+                printk(KERN_WARNING "md: %s: %s would not accept array\n",
+                       mdname(mddev), level);
+                return PTR_ERR(priv);
+        }
+
+        /* Looks like we have a winner */
+        mddev_suspend(mddev);
+        mddev->pers->stop(mddev);
+        module_put(mddev->pers->owner);
+        mddev->pers = pers;
+        mddev->private = priv;
+        strlcpy(mddev->clevel, pers->name, sizeof(mddev->clevel));
+        mddev->level = mddev->new_level;
+        mddev->layout = mddev->new_layout;
+        mddev->chunk_size = mddev->new_chunk;
+        mddev->delta_disks = 0;
+        pers->run(mddev);
+        mddev_resume(mddev);
+        set_bit(MD_CHANGE_DEVS, &mddev->flags);
+        set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
+        md_wakeup_thread(mddev->thread);
         return rv;
 }