md: support 'external' metadata for md arrays

- Add a state flag 'external' to indicate that the metadata is managed
  externally (by user-space) so important changes need to be
  left of user-space to handle.
  Alternates are non-persistant ('none') where there is no stable metadata -
  after the  array is stopped there is no record of it's status - and
  internal which can be version 0.90 or version 1.x
  These are selected by writing to the 'metadata' attribute.

- move the updating of superblocks (sync_sbs) to after we have checked if
  there are any superblocks or not.

- New array state 'write_pending'.  This means that the metadata records
  the array as 'clean', but a write has been requested, so the metadata has
  to be updated to record a 'dirty' array before the write can continue.
  This change is reported to md by writing 'active' to the array_state
  attribute.

- tidy up marking of sb_dirty:
   - don't set sb_dirty when resync finishes as md_check_recovery
     calls md_update_sb when the sync thread finishes anyway.
   - Don't set sb_dirty in multipath_run as the array might not be dirty.
   - don't mark superblock dirty when switching to 'clean' if there
     is no internal superblock (if external, userspace can choose to
     update the superblock whenever it chooses to).

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>

2 files changed, 61 insertions, 19 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index c28a120b4161..e2782a04012d 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -778,7 +778,8 @@ static int super_90_validate(mddev_t *mddev, mdk_rdev_t *rdev)
                 mddev->major_version = 0;
                 mddev->minor_version = sb->minor_version;
                 mddev->patch_version = sb->patch_version;
-                mddev->persistent = ! sb->not_persistent;
+                mddev->persistent = 1;
+                mddev->external = 0;
                 mddev->chunk_size = sb->chunk_size;
                 mddev->ctime = sb->ctime;
                 mddev->utime = sb->utime;
@@ -904,7 +905,7 @@ static void super_90_sync(mddev_t *mddev, mdk_rdev_t *rdev)
         sb->size  = mddev->size;
         sb->raid_disks = mddev->raid_disks;
         sb->md_minor = mddev->md_minor;
-        sb->not_persistent = !mddev->persistent;
+        sb->not_persistent = 0;
         sb->utime = mddev->utime;
         sb->state = 0;
         sb->events_hi = (mddev->events>>32);
@@ -1158,6 +1159,7 @@ static int super_1_validate(mddev_t *mddev, mdk_rdev_t *rdev)
                 mddev->major_version = 1;
                 mddev->patch_version = 0;
                 mddev->persistent = 1;
+                mddev->external = 0;
                 mddev->chunk_size = le32_to_cpu(sb->chunksize) << 9;
                 mddev->ctime = le64_to_cpu(sb->ctime) & ((1ULL << 32)-1);
                 mddev->utime = le64_to_cpu(sb->utime) & ((1ULL << 32)-1);
@@ -1696,18 +1698,20 @@ repeat:
                 MD_BUG();
                 mddev->events --;
         }
-        sync_sbs(mddev, nospares);
 
         /*
          * do not write anything to disk if using
          * nonpersistent superblocks
          */
         if (!mddev->persistent) {
-                clear_bit(MD_CHANGE_PENDING, &mddev->flags);
+                if (!mddev->external)
+                        clear_bit(MD_CHANGE_PENDING, &mddev->flags);
+
                 spin_unlock_irq(&mddev->write_lock);
                 wake_up(&mddev->sb_wait);
                 return;
         }
+        sync_sbs(mddev, nospares);
         spin_unlock_irq(&mddev->write_lock);
 
         dprintk(KERN_INFO 
@@ -2425,6 +2429,8 @@ array_state_show(mddev_t *mddev, char *page)
                 case 0:
                         if (mddev->in_sync)
                                 st = clean;
+                        else if (test_bit(MD_CHANGE_CLEAN, &mddev->flags))
+                                st = write_pending;
                         else if (mddev->safemode)
                                 st = active_idle;
                         else
@@ -2455,11 +2461,9 @@ array_state_store(mddev_t *mddev, const char *buf, size_t len)
                 break;
         case clear:
                 /* stopping an active array */
-                if (mddev->pers) {
-                        if (atomic_read(&mddev->active) > 1)
-                                return -EBUSY;
-                        err = do_md_stop(mddev, 0);
-                }
+                if (atomic_read(&mddev->active) > 1)
+                        return -EBUSY;
+                err = do_md_stop(mddev, 0);
                 break;
         case inactive:
                 /* stopping an active array */
@@ -2467,7 +2471,8 @@ array_state_store(mddev_t *mddev, const char *buf, size_t len)
                         if (atomic_read(&mddev->active) > 1)
                                 return -EBUSY;
                         err = do_md_stop(mddev, 2);
-                }
+                } else
+                        err = 0; /* already inactive */
                 break;
         case suspended:
                 break; /* not supported yet */
@@ -2495,9 +2500,15 @@ array_state_store(mddev_t *mddev, const char *buf, size_t len)
                         restart_array(mddev);
                         spin_lock_irq(&mddev->write_lock);
                         if (atomic_read(&mddev->writes_pending) == 0) {
-                                mddev->in_sync = 1;
-                                set_bit(MD_CHANGE_CLEAN, &mddev->flags);
-                        }
+                                if (mddev->in_sync == 0) {
+                                        mddev->in_sync = 1;
+                                        if (mddev->persistent)
+                                                set_bit(MD_CHANGE_CLEAN,
+                                                        &mddev->flags);
+                                }
+                                err = 0;
+                        } else
+                                err = -EBUSY;
                         spin_unlock_irq(&mddev->write_lock);
                 } else {
                         mddev->ro = 0;
@@ -2508,7 +2519,8 @@ array_state_store(mddev_t *mddev, const char *buf, size_t len)
         case active:
                 if (mddev->pers) {
                         restart_array(mddev);
-                        clear_bit(MD_CHANGE_CLEAN, &mddev->flags);
+                        if (mddev->external)
+                                clear_bit(MD_CHANGE_CLEAN, &mddev->flags);
                         wake_up(&mddev->sb_wait);
                         err = 0;
                 } else {
@@ -2659,7 +2671,9 @@ __ATTR(component_size, S_IRUGO|S_IWUSR, size_show, size_store);
 
 
 /* Metdata version.
- * This is either 'none' for arrays with externally managed metadata,
+ * This is one of
+ *   'none' for arrays with no metadata (good luck...)
+ *   'external' for arrays with externally managed metadata,
  * or N.M for internally known formats
  */
 static ssize_t
@@ -2668,6 +2682,8 @@ metadata_show(mddev_t *mddev, char *page)
         if (mddev->persistent)
                 return sprintf(page, "%d.%d\n",
                                mddev->major_version, mddev->minor_version);
+        else if (mddev->external)
+                return sprintf(page, "external:%s\n", mddev->metadata_type);
         else
                 return sprintf(page, "none\n");
 }
@@ -2682,6 +2698,21 @@ metadata_store(mddev_t *mddev, const char *buf, size_t len)
 
         if (cmd_match(buf, "none")) {
                 mddev->persistent = 0;
+                mddev->external = 0;
+                mddev->major_version = 0;
+                mddev->minor_version = 90;
+                return len;
+        }
+        if (strncmp(buf, "external:", 9) == 0) {
+                int namelen = len-9;
+                if (namelen >= sizeof(mddev->metadata_type))
+                        namelen = sizeof(mddev->metadata_type)-1;
+                strncpy(mddev->metadata_type, buf+9, namelen);
+                mddev->metadata_type[namelen] = 0;
+                if (namelen && mddev->metadata_type[namelen-1] == '\n')
+                        mddev->metadata_type[--namelen] = 0;
+                mddev->persistent = 0;
+                mddev->external = 1;
                 mddev->major_version = 0;
                 mddev->minor_version = 90;
                 return len;
@@ -2698,6 +2729,7 @@ metadata_store(mddev_t *mddev, const char *buf, size_t len)
         mddev->major_version = major;
         mddev->minor_version = minor;
         mddev->persistent = 1;
+        mddev->external = 0;
         return len;
 }
 
@@ -3524,6 +3556,7 @@ static int do_md_stop(mddev_t * mddev, int mode)
                 mddev->raid_disks = 0;
                 mddev->recovery_cp = 0;
                 mddev->reshape_position = MaxSector;
+                mddev->external = 0;
 
         } else if (mddev->pers)
                 printk(KERN_INFO "md: %s switched to read-only mode.\n",
@@ -4165,13 +4198,15 @@ static int set_array_info(mddev_t * mddev, mdu_array_info_t *info)
         else
                 mddev->recovery_cp = 0;
         mddev->persistent    = ! info->not_persistent;
+        mddev->external      = 0;
 
         mddev->layout        = info->layout;
         mddev->chunk_size    = info->chunk_size;
 
         mddev->max_disks     = MD_SB_DISKS;
 
-        mddev->flags         = 0;
+        if (mddev->persistent)
+                mddev->flags         = 0;
         set_bit(MD_CHANGE_DEVS, &mddev->flags);
 
         mddev->default_bitmap_offset = MD_SB_BYTES >> 9;
@@ -4982,7 +5017,10 @@ static int md_seq_show(struct seq_file *seq, void *v)
                                            mddev->major_version,
                                            mddev->minor_version);
                         }
-                } else
+                } else if (mddev->external)
+                        seq_printf(seq, " super external:%s",
+                                   mddev->metadata_type);
+                else
                         seq_printf(seq, " super non-persistent");
 
                 if (mddev->pers) {
@@ -5589,7 +5627,7 @@ void md_check_recovery(mddev_t *mddev)
         }
 
         if ( ! (
-                mddev->flags ||
+                (mddev->flags && !mddev->external) ||
                 test_bit(MD_RECOVERY_NEEDED, &mddev->recovery) ||
                 test_bit(MD_RECOVERY_DONE, &mddev->recovery) ||
                 (mddev->safemode == 1) ||
@@ -5605,7 +5643,8 @@ void md_check_recovery(mddev_t *mddev)
                 if (mddev->safemode && !atomic_read(&mddev->writes_pending) &&
                     !mddev->in_sync && mddev->recovery_cp == MaxSector) {
                         mddev->in_sync = 1;
-                        set_bit(MD_CHANGE_CLEAN, &mddev->flags);
+                        if (mddev->persistent)
+                                set_bit(MD_CHANGE_CLEAN, &mddev->flags);
                 }
                 if (mddev->safemode == 1)
                         mddev->safemode = 0;
diff --git a/include/linux/raid/md_k.h b/include/linux/raid/md_k.h
index dcb729244f47..b579cc628303 100644
--- a/include/linux/raid/md_k.h
+++ b/include/linux/raid/md_k.h
@@ -130,6 +130,9 @@ struct mddev_s
                                         minor_version,
                                         patch_version;
         int                             persistent;
+        int                             external;       /* metadata is
+                                                         * managed externally */
+        char                            metadata_type[17]; /* externally set*/
         int                             chunk_size;
         time_t                          ctime, utime;
         int                             level, layout;