nilfs2: add bdev freeze/thaw support

Nilfs hasn't supported the freeze/thaw feature because it didn't work
due to the peculiar design that multiple super block instances could
be allocated for a device.  This limitation was removed by the patch
"nilfs2: do not allocate multiple super block instances for a device".

So now this adds the freeze/thaw support to nilfs.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

1 files changed, 54 insertions, 4 deletions

diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
index a1cd444103ff..92e8c769584c 100644
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -73,6 +73,7 @@ struct kmem_cache *nilfs_transaction_cachep;
 struct kmem_cache *nilfs_segbuf_cachep;
 struct kmem_cache *nilfs_btree_path_cache;
 
+static int nilfs_setup_super(struct nilfs_sb_info *sbi, int is_mount);
 static int nilfs_remount(struct super_block *sb, int *flags, char *data);
 
 static void nilfs_set_error(struct nilfs_sb_info *sbi)
@@ -439,6 +440,36 @@ int nilfs_attach_checkpoint(struct nilfs_sb_info *sbi, __u64 cno, int curr_mnt,
         return err;
 }
 
+static int nilfs_freeze(struct super_block *sb)
+{
+        struct nilfs_sb_info *sbi = NILFS_SB(sb);
+        struct the_nilfs *nilfs = sbi->s_nilfs;
+        int err;
+
+        if (sb->s_flags & MS_RDONLY)
+                return 0;
+
+        /* Mark super block clean */
+        down_write(&nilfs->ns_sem);
+        err = nilfs_cleanup_super(sbi);
+        up_write(&nilfs->ns_sem);
+        return err;
+}
+
+static int nilfs_unfreeze(struct super_block *sb)
+{
+        struct nilfs_sb_info *sbi = NILFS_SB(sb);
+        struct the_nilfs *nilfs = sbi->s_nilfs;
+
+        if (sb->s_flags & MS_RDONLY)
+                return 0;
+
+        down_write(&nilfs->ns_sem);
+        nilfs_setup_super(sbi, false);
+        up_write(&nilfs->ns_sem);
+        return 0;
+}
+
 static int nilfs_statfs(struct dentry *dentry, struct kstatfs *buf)
 {
         struct super_block *sb = dentry->d_sb;
@@ -523,6 +554,8 @@ static const struct super_operations nilfs_sops = {
         .put_super      = nilfs_put_super,
         /* .write_super    = nilfs_write_super, */
         .sync_fs        = nilfs_sync_fs,
+        .freeze_fs      = nilfs_freeze,
+        .unfreeze_fs    = nilfs_unfreeze,
         /* .write_super_lockfs */
         /* .unlockfs */
         .statfs         = nilfs_statfs,
@@ -626,7 +659,7 @@ nilfs_set_default_options(struct nilfs_sb_info *sbi,
                 NILFS_MOUNT_ERRORS_RO | NILFS_MOUNT_BARRIER;
 }
 
-static int nilfs_setup_super(struct nilfs_sb_info *sbi)
+static int nilfs_setup_super(struct nilfs_sb_info *sbi, int is_mount)
 {
         struct the_nilfs *nilfs = sbi->s_nilfs;
         struct nilfs_super_block **sbp;
@@ -638,6 +671,9 @@ static int nilfs_setup_super(struct nilfs_sb_info *sbi)
         if (!sbp)
                 return -EIO;
 
+        if (!is_mount)
+                goto skip_mount_setup;
+
         max_mnt_count = le16_to_cpu(sbp[0]->s_max_mnt_count);
         mnt_count = le16_to_cpu(sbp[0]->s_mnt_count);
 
@@ -654,9 +690,11 @@ static int nilfs_setup_super(struct nilfs_sb_info *sbi)
                 sbp[0]->s_max_mnt_count = cpu_to_le16(NILFS_DFL_MAX_MNT_COUNT);
 
         sbp[0]->s_mnt_count = cpu_to_le16(mnt_count + 1);
+        sbp[0]->s_mtime = cpu_to_le64(get_seconds());
+
+skip_mount_setup:
         sbp[0]->s_state =
                 cpu_to_le16(le16_to_cpu(sbp[0]->s_state) & ~NILFS_VALID_FS);
-        sbp[0]->s_mtime = cpu_to_le64(get_seconds());
         /* synchronize sbp[1] with sbp[0] */
         memcpy(sbp[1], sbp[0], nilfs->ns_sbsize);
         return nilfs_commit_super(sbi, NILFS_SB_COMMIT_ALL);
@@ -938,7 +976,7 @@ nilfs_fill_super(struct super_block *sb, void *data, int silent)
 
         if (!(sb->s_flags & MS_RDONLY)) {
                 down_write(&nilfs->ns_sem);
-                nilfs_setup_super(sbi);
+                nilfs_setup_super(sbi, true);
                 up_write(&nilfs->ns_sem);
         }
 
@@ -1034,7 +1072,7 @@ static int nilfs_remount(struct super_block *sb, int *flags, char *data)
                         goto restore_opts;
 
                 down_write(&nilfs->ns_sem);
-                nilfs_setup_super(sbi);
+                nilfs_setup_super(sbi, true);
                 up_write(&nilfs->ns_sem);
         }
  out:
@@ -1132,7 +1170,19 @@ nilfs_get_sb(struct file_system_type *fs_type, int flags,
                 goto failed;
         }
 
+        /*
+         * once the super is inserted into the list by sget, s_umount
+         * will protect the lockfs code from trying to start a snapshot
+         * while we are mounting
+         */
+        mutex_lock(&sd.bdev->bd_fsfreeze_mutex);
+        if (sd.bdev->bd_fsfreeze_count > 0) {
+                mutex_unlock(&sd.bdev->bd_fsfreeze_mutex);
+                err = -EBUSY;
+                goto failed;
+        }
         s = sget(fs_type, nilfs_test_bdev_super, nilfs_set_bdev_super, sd.bdev);
+        mutex_unlock(&sd.bdev->bd_fsfreeze_mutex);
         if (IS_ERR(s)) {
                 err = PTR_ERR(s);
                 goto failed;