filesystem freeze: implement generic freeze feature

[linux-2.6-omap-h63xx.git] / fs / buffer.c

diff --git a/fs/buffer.c b/fs/buffer.c
index 87f9e537b8c31eec7073c298a07bb80ea223d213..b6e8b8632e2f973718dda48d0247e961569105df 100644 (file)
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -203,10 +203,25 @@ int fsync_bdev(struct block_device *bdev)
  * happen on bdev until thaw_bdev() is called.
  * If a superblock is found on this device, we take the s_umount semaphore
  * on it to make sure nobody unmounts until the snapshot creation is done.
+ * The reference counter (bd_fsfreeze_count) guarantees that only the last
+ * unfreeze process can unfreeze the frozen filesystem actually when multiple
+ * freeze requests arrive simultaneously. It counts up in freeze_bdev() and
+ * count down in thaw_bdev(). When it becomes 0, thaw_bdev() will unfreeze
+ * actually.
  */
 struct super_block *freeze_bdev(struct block_device *bdev)
 {
        struct super_block *sb;
+       int error = 0;
+
+       mutex_lock(&bdev->bd_fsfreeze_mutex);
+       if (bdev->bd_fsfreeze_count > 0) {
+               bdev->bd_fsfreeze_count++;
+               sb = get_super(bdev);
+               mutex_unlock(&bdev->bd_fsfreeze_mutex);
+               return sb;
+       }
+       bdev->bd_fsfreeze_count++;
 
        down(&bdev->bd_mount_sem);
        sb = get_super(bdev);
@@ -221,11 +236,24 @@ struct super_block *freeze_bdev(struct block_device *bdev)
 
                sync_blockdev(sb->s_bdev);
 
-               if (sb->s_op->freeze_fs)
-                       sb->s_op->freeze_fs(sb);
+               if (sb->s_op->freeze_fs) {
+                       error = sb->s_op->freeze_fs(sb);
+                       if (error) {
+                               printk(KERN_ERR
+                                       "VFS:Filesystem freeze failed\n");
+                               sb->s_frozen = SB_UNFROZEN;
+                               drop_super(sb);
+                               up(&bdev->bd_mount_sem);
+                               bdev->bd_fsfreeze_count--;
+                               mutex_unlock(&bdev->bd_fsfreeze_mutex);
+                               return ERR_PTR(error);
+                       }
+               }
        }
 
        sync_blockdev(bdev);
+       mutex_unlock(&bdev->bd_fsfreeze_mutex);
+
        return sb;      /* thaw_bdev releases s->s_umount and bd_mount_sem */
 }
 EXPORT_SYMBOL(freeze_bdev);
@@ -237,20 +265,48 @@ EXPORT_SYMBOL(freeze_bdev);
  *
  * Unlocks the filesystem and marks it writeable again after freeze_bdev().
  */
-void thaw_bdev(struct block_device *bdev, struct super_block *sb)
+int thaw_bdev(struct block_device *bdev, struct super_block *sb)
 {
+       int error = 0;
+
+       mutex_lock(&bdev->bd_fsfreeze_mutex);
+       if (!bdev->bd_fsfreeze_count) {
+               mutex_unlock(&bdev->bd_fsfreeze_mutex);
+               return -EINVAL;
+       }
+
+       bdev->bd_fsfreeze_count--;
+       if (bdev->bd_fsfreeze_count > 0) {
+               if (sb)
+                       drop_super(sb);
+               mutex_unlock(&bdev->bd_fsfreeze_mutex);
+               return 0;
+       }
+
        if (sb) {
                BUG_ON(sb->s_bdev != bdev);
-
-               if (sb->s_op->unfreeze_fs)
-                       sb->s_op->unfreeze_fs(sb);
-               sb->s_frozen = SB_UNFROZEN;
-               smp_wmb();
-               wake_up(&sb->s_wait_unfrozen);
+               if (!(sb->s_flags & MS_RDONLY)) {
+                       if (sb->s_op->unfreeze_fs) {
+                               error = sb->s_op->unfreeze_fs(sb);
+                               if (error) {
+                                       printk(KERN_ERR
+                                               "VFS:Filesystem thaw failed\n");
+                                       sb->s_frozen = SB_FREEZE_TRANS;
+                                       bdev->bd_fsfreeze_count++;
+                                       mutex_unlock(&bdev->bd_fsfreeze_mutex);
+                                       return error;
+                               }
+                       }
+                       sb->s_frozen = SB_UNFROZEN;
+                       smp_wmb();
+                       wake_up(&sb->s_wait_unfrozen);
+               }
                drop_super(sb);
        }
 
        up(&bdev->bd_mount_sem);
+       mutex_unlock(&bdev->bd_fsfreeze_mutex);
+       return 0;
 }
 EXPORT_SYMBOL(thaw_bdev);