nilfs2: do not allocate multiple super block instances for a device

This stops allocating multiple super block instances for a device.

All snapshots and a current mode mount (i.e. latest tree) will be
controlled with nilfs_root objects that are kept within an sb
instance.

nilfs_get_sb() is rewritten so that it always has a root object for
the latest tree and snapshots make additional root objects.

The root dentry of the latest tree is binded to sb->s_root even if it
isn't attached on a directory.  Root dentries of snapshots or the
latest tree are binded to mnt->mnt_root on which they are mounted.

With this patch, nilfs_find_sbinfo() function, nilfs->ns_supers list,
and nilfs->ns_current back pointer, are deleted.  In addition,
init_nilfs() and load_nilfs() are simplified since they will be called
once for a device, not repeatedly called for mount points.

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

diff --git a/fs/nilfs2/sb.h b/fs/nilfs2/sb.h
index 3cc3675..35a0715 100644 (file)
--- a/fs/nilfs2/sb.h
+++ b/fs/nilfs2/sb.h
@@ -42,9 +42,6 @@ struct nilfs_sc_info;
  * NILFS super-block data in memory
  */
 struct nilfs_sb_info {
-       /* Snapshot status */
-       __u64 s_snapshot_cno;           /* Checkpoint number */
-
        /* Mount options */
        unsigned long s_mount_opt;
        uid_t s_resuid;
@@ -57,8 +54,6 @@ struct nilfs_sb_info {
        /* Fundamental members */
        struct super_block *s_super;    /* reverse pointer to super_block */
        struct the_nilfs *s_nilfs;
-       struct list_head s_list;        /* list head for nilfs->ns_supers */
-       atomic_t s_count;               /* reference count */
 
        /* Segment constructor */
        struct list_head s_dirty_files; /* dirty files list */

diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
index ebeb746..2e58e7c 100644 (file)
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -355,16 +355,11 @@ static void nilfs_put_super(struct super_block *sb)
                nilfs_cleanup_super(sbi);
                up_write(&nilfs->ns_sem);
        }
-       down_write(&nilfs->ns_super_sem);
-       if (nilfs->ns_current == sbi)
-               nilfs->ns_current = NULL;
-       list_del_init(&sbi->s_list);
-       up_write(&nilfs->ns_super_sem);
 
        put_nilfs(sbi->s_nilfs);
        sbi->s_super = NULL;
        sb->s_fs_info = NULL;
-       nilfs_put_sbinfo(sbi);
+       kfree(sbi);
 }
 
 static int nilfs_sync_fs(struct super_block *sb, int wait)
@@ -500,12 +495,12 @@ static int nilfs_show_options(struct seq_file *seq, struct vfsmount *vfs)
 {
        struct super_block *sb = vfs->mnt_sb;
        struct nilfs_sb_info *sbi = NILFS_SB(sb);
+       struct nilfs_root *root = NILFS_I(vfs->mnt_root->d_inode)->i_root;
 
        if (!nilfs_test_opt(sbi, BARRIER))
                seq_puts(seq, ",nobarrier");
-       if (nilfs_test_opt(sbi, SNAPSHOT))
-               seq_printf(seq, ",cp=%llu",
-                          (unsigned long long int)sbi->s_snapshot_cno);
+       if (root->cno != NILFS_CPTREE_CURRENT_CNO)
+               seq_printf(seq, ",cp=%llu", (unsigned long long)root->cno);
        if (nilfs_test_opt(sbi, ERRORS_PANIC))
                seq_puts(seq, ",errors=panic");
        if (nilfs_test_opt(sbi, ERRORS_CONT))
@@ -605,27 +600,11 @@ static int parse_options(char *options, struct super_block *sb, int is_remount)
                        if (match_int(&args[0], &option) || option <= 0)
                                return 0;
                        if (is_remount) {
-                               if (!nilfs_test_opt(sbi, SNAPSHOT)) {
-                                       printk(KERN_ERR
-                                              "NILFS: cannot change regular "
-                                              "mount to snapshot.\n");
-                                       return 0;
-                               } else if (option != sbi->s_snapshot_cno) {
-                                       printk(KERN_ERR
-                                              "NILFS: cannot remount to a "
-                                              "different snapshot.\n");
-                                       return 0;
-                               }
-                               break;
-                       }
-                       if (!(sb->s_flags & MS_RDONLY)) {
-                               printk(KERN_ERR "NILFS: cannot mount snapshot "
-                                      "read/write.  A read-only option is "
-                                      "required.\n");
+                               printk(KERN_ERR
+                                      "NILFS: \"%s\" option is invalid "
+                                      "for remount.\n", p);
                                return 0;
                        }
-                       sbi->s_snapshot_cno = option;
-                       nilfs_set_opt(sbi, SNAPSHOT);
                        break;
                case Opt_norecovery:
                        nilfs_set_opt(sbi, NORECOVERY);
@@ -771,16 +750,32 @@ static int nilfs_get_root_dentry(struct super_block *sb,
                goto out;
        }
 
-       dentry = d_alloc_root(inode);
-       if (!dentry) {
-               iput(inode);
-               printk(KERN_ERR "NILFS: get root dentry failed\n");
-               ret = -ENOMEM;
-               goto out;
+       if (root->cno == NILFS_CPTREE_CURRENT_CNO) {
+               dentry = d_find_alias(inode);
+               if (!dentry) {
+                       dentry = d_alloc_root(inode);
+                       if (!dentry) {
+                               iput(inode);
+                               ret = -ENOMEM;
+                               goto failed_dentry;
+                       }
+               } else {
+                       iput(inode);
+               }
+       } else {
+               dentry = d_obtain_alias(inode);
+               if (IS_ERR(dentry)) {
+                       ret = PTR_ERR(dentry);
+                       goto failed_dentry;
+               }
        }
        *root_dentry = dentry;
  out:
        return ret;
+
+ failed_dentry:
+       printk(KERN_ERR "NILFS: get root dentry failed\n");
+       goto out;
 }
 
 static int nilfs_attach_snapshot(struct super_block *s, __u64 cno,
@@ -817,6 +812,25 @@ static int nilfs_attach_snapshot(struct super_block *s, __u64 cno,
        return ret;
 }
 
+static int nilfs_tree_was_touched(struct dentry *root_dentry)
+{
+       return atomic_read(&root_dentry->d_count) > 1;
+}
+
+/**
+ * nilfs_try_to_shrink_tree() - try to shrink dentries of a checkpoint
+ * @root_dentry: root dentry of the tree to be shrunk
+ *
+ * This function returns true if the tree was in-use.
+ */
+static int nilfs_try_to_shrink_tree(struct dentry *root_dentry)
+{
+       if (have_submounts(root_dentry))
+               return true;
+       shrink_dcache_parent(root_dentry);
+       return nilfs_tree_was_touched(root_dentry);
+}
+
 /**
  * nilfs_fill_super() - initialize a super block instance
  * @sb: super_block
@@ -845,7 +859,6 @@ nilfs_fill_super(struct super_block *sb, void *data, int silent,
        get_nilfs(nilfs);
        sbi->s_nilfs = nilfs;
        sbi->s_super = sb;
-       atomic_set(&sbi->s_count, 1);
 
        err = init_nilfs(nilfs, sbi, (char *)data);
        if (err)
@@ -853,7 +866,6 @@ nilfs_fill_super(struct super_block *sb, void *data, int silent,
 
        spin_lock_init(&sbi->s_inode_lock);
        INIT_LIST_HEAD(&sbi->s_dirty_files);
-       INIT_LIST_HEAD(&sbi->s_list);
 
        /*
         * Following initialization is overlapped because
@@ -875,20 +887,11 @@ nilfs_fill_super(struct super_block *sb, void *data, int silent,
        if (err)
                goto failed_sbi;
 
-       if (nilfs_test_opt(sbi, SNAPSHOT)) {
-               err = nilfs_attach_snapshot(sb, sbi->s_snapshot_cno,
-                                           &sb->s_root);
-               if (err)
-                       goto failed_sbi;
-
-               goto add_to_supers;
-       }
-
        cno = nilfs_last_cno(nilfs);
        err = nilfs_attach_checkpoint(sbi, cno, true, &fsroot);
        if (err) {
-               printk(KERN_ERR "NILFS: error loading a checkpoint"
-                      " (checkpoint number=%llu).\n", (unsigned long long)cno);
+               printk(KERN_ERR "NILFS: error loading last checkpoint "
+                      "(checkpoint number=%llu).\n", (unsigned long long)cno);
                goto failed_sbi;
        }
 
@@ -910,13 +913,6 @@ nilfs_fill_super(struct super_block *sb, void *data, int silent,
                up_write(&nilfs->ns_sem);
        }
 
- add_to_supers:
-       down_write(&nilfs->ns_super_sem);
-       list_add(&sbi->s_list, &nilfs->ns_supers);
-       if (!nilfs_test_opt(sbi, SNAPSHOT))
-               nilfs->ns_current = sbi;
-       up_write(&nilfs->ns_super_sem);
-
        return 0;
 
  failed_segctor:
@@ -928,7 +924,7 @@ nilfs_fill_super(struct super_block *sb, void *data, int silent,
  failed_sbi:
        put_nilfs(nilfs);
        sb->s_fs_info = NULL;
-       nilfs_put_sbinfo(sbi);
+       kfree(sbi);
        return err;
 }
 
@@ -938,13 +934,10 @@ static int nilfs_remount(struct super_block *sb, int *flags, char *data)
        struct the_nilfs *nilfs = sbi->s_nilfs;
        unsigned long old_sb_flags;
        struct nilfs_mount_options old_opts;
-       int was_snapshot, err;
+       int err;
 
-       down_write(&nilfs->ns_super_sem);
        old_sb_flags = sb->s_flags;
        old_opts.mount_opt = sbi->s_mount_opt;
-       old_opts.snapshot_cno = sbi->s_snapshot_cno;
-       was_snapshot = nilfs_test_opt(sbi, SNAPSHOT);
 
        if (!parse_options(data, sb, 1)) {
                err = -EINVAL;
@@ -953,11 +946,6 @@ static int nilfs_remount(struct super_block *sb, int *flags, char *data)
        sb->s_flags = (sb->s_flags & ~MS_POSIXACL);
 
        err = -EINVAL;
-       if (was_snapshot && !(*flags & MS_RDONLY)) {
-               printk(KERN_ERR "NILFS (device %s): cannot remount snapshot "
-                      "read/write.\n", sb->s_id);
-               goto restore_opts;
-       }
 
        if (!nilfs_valid_fs(nilfs)) {
                printk(KERN_WARNING "NILFS (device %s): couldn't "
@@ -1014,14 +1002,11 @@ static int nilfs_remount(struct super_block *sb, int *flags, char *data)
                up_write(&nilfs->ns_sem);
        }
  out:
-       up_write(&nilfs->ns_super_sem);
        return 0;
 
  restore_opts:
        sb->s_flags = old_sb_flags;
        sbi->s_mount_opt = old_opts.mount_opt;
-       sbi->s_snapshot_cno = old_opts.snapshot_cno;
-       up_write(&nilfs->ns_super_sem);
        return err;
 }
 
@@ -1075,18 +1060,14 @@ static int nilfs_identify(char *data, struct nilfs_super_data *sd)
 
 static int nilfs_set_bdev_super(struct super_block *s, void *data)
 {
-       struct nilfs_super_data *sd = data;
-
-       s->s_bdev = sd->bdev;
+       s->s_bdev = data;
        s->s_dev = s->s_bdev->bd_dev;
        return 0;
 }
 
 static int nilfs_test_bdev_super(struct super_block *s, void *data)
 {
-       struct nilfs_super_data *sd = data;
-
-       return sd->sbi && s->s_fs_info == (void *)sd->sbi;
+       return (void *)s->s_bdev == data;
 }
 
 static int
@@ -1097,7 +1078,8 @@ nilfs_get_sb(struct file_system_type *fs_type, int flags,
        struct super_block *s;
        fmode_t mode = FMODE_READ;
        struct the_nilfs *nilfs;
-       int err, need_to_close = 1;
+       struct dentry *root_dentry;
+       int err, s_new = false;
 
        if (!(flags & MS_RDONLY))
                mode |= FMODE_WRITE;
@@ -1106,12 +1088,6 @@ nilfs_get_sb(struct file_system_type *fs_type, int flags,
        if (IS_ERR(sd.bdev))
                return PTR_ERR(sd.bdev);
 
-       /*
-        * To get mount instance using sget() vfs-routine, NILFS needs
-        * much more information than normal filesystems to identify mount
-        * instance.  For snapshot mounts, not only a mount type (ro-mount
-        * or rw-mount) but also a checkpoint number is required.
-        */
        sd.cno = 0;
        sd.flags = flags;
        if (nilfs_identify((char *)data, &sd)) {
@@ -1127,38 +1103,7 @@ nilfs_get_sb(struct file_system_type *fs_type, int flags,
 
        mutex_lock(&nilfs->ns_mount_mutex);
 
-       if (!sd.cno) {
-               /*
-                * Check if an exclusive mount exists or not.
-                * Snapshot mounts coexist with a current mount
-                * (i.e. rw-mount or ro-mount), whereas rw-mount and
-                * ro-mount are mutually exclusive.
-                */
-               down_read(&nilfs->ns_super_sem);
-               if (nilfs->ns_current &&
-                   ((nilfs->ns_current->s_super->s_flags ^ flags)
-                    & MS_RDONLY)) {
-                       up_read(&nilfs->ns_super_sem);
-                       err = -EBUSY;
-                       goto failed_unlock;
-               }
-               up_read(&nilfs->ns_super_sem);
-       }
-
-       /*
-        * Find existing nilfs_sb_info struct
-        */
-       sd.sbi = nilfs_find_sbinfo(nilfs, !(flags & MS_RDONLY), sd.cno);
-
-       /*
-        * Get super block instance holding the nilfs_sb_info struct.
-        * A new instance is allocated if no existing mount is present or
-        * existing instance has been unmounted.
-        */
-       s = sget(fs_type, nilfs_test_bdev_super, nilfs_set_bdev_super, &sd);
-       if (sd.sbi)
-               nilfs_put_sbinfo(sd.sbi);
-
+       s = sget(fs_type, nilfs_test_bdev_super, nilfs_set_bdev_super, sd.bdev);
        if (IS_ERR(s)) {
                err = PTR_ERR(s);
                goto failed_unlock;
@@ -1167,6 +1112,8 @@ nilfs_get_sb(struct file_system_type *fs_type, int flags,
        if (!s->s_root) {
                char b[BDEVNAME_SIZE];
 
+               s_new = true;
+
                /* New superblock instance created */
                s->s_flags = flags;
                s->s_mode = mode;
@@ -1179,16 +1126,53 @@ nilfs_get_sb(struct file_system_type *fs_type, int flags,
                        goto cancel_new;
 
                s->s_flags |= MS_ACTIVE;
-               need_to_close = 0;
+       } else if (!sd.cno) {
+               int busy = false;
+
+               if (nilfs_tree_was_touched(s->s_root)) {
+                       busy = nilfs_try_to_shrink_tree(s->s_root);
+                       if (busy && (flags ^ s->s_flags) & MS_RDONLY) {
+                               printk(KERN_ERR "NILFS: the device already "
+                                      "has a %s mount.\n",
+                                      (s->s_flags & MS_RDONLY) ?
+                                      "read-only" : "read/write");
+                               err = -EBUSY;
+                               goto failed_super;
+                       }
+               }
+               if (!busy) {
+                       /*
+                        * Try remount to setup mount states if the current
+                        * tree is not mounted and only snapshots use this sb.
+                        */
+                       err = nilfs_remount(s, &flags, data);
+                       if (err)
+                               goto failed_super;
+               }
+       }
+
+       if (sd.cno) {
+               err = nilfs_attach_snapshot(s, sd.cno, &root_dentry);
+               if (err) {
+                       if (s_new)
+                               goto cancel_new;
+                       goto failed_super;
+               }
+       } else {
+               root_dentry = dget(s->s_root);
        }
 
        mutex_unlock(&nilfs->ns_mount_mutex);
        put_nilfs(nilfs);
-       if (need_to_close)
+       if (!s_new)
                close_bdev_exclusive(sd.bdev, mode);
-       simple_set_mnt(mnt, s);
+
+       mnt->mnt_sb = s;
+       mnt->mnt_root = root_dentry;
        return 0;
 
+ failed_super:
+       deactivate_locked_super(s);
  failed_unlock:
        mutex_unlock(&nilfs->ns_mount_mutex);
        put_nilfs(nilfs);
@@ -1202,7 +1186,7 @@ nilfs_get_sb(struct file_system_type *fs_type, int flags,
        put_nilfs(nilfs);
        deactivate_locked_super(s);
        /*
-        * deactivate_locked_super() invokes close_bdev_exclusive().
+        * This deactivate_locked_super() invokes close_bdev_exclusive().
         * We must finish all post-cleaning before this call;
         * put_nilfs() needs the block device.
         */

diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
index 89c7856..960c287 100644 (file)
--- a/fs/nilfs2/the_nilfs.c
+++ b/fs/nilfs2/the_nilfs.c
@@ -82,11 +82,9 @@ static struct the_nilfs *alloc_nilfs(struct block_device *bdev)
        atomic_set(&nilfs->ns_count, 1);
        atomic_set(&nilfs->ns_ndirtyblks, 0);
        init_rwsem(&nilfs->ns_sem);
-       init_rwsem(&nilfs->ns_super_sem);
        mutex_init(&nilfs->ns_mount_mutex);
        init_rwsem(&nilfs->ns_writer_sem);
        INIT_LIST_HEAD(&nilfs->ns_list);
-       INIT_LIST_HEAD(&nilfs->ns_supers);
        INIT_LIST_HEAD(&nilfs->ns_gc_inodes);
        spin_lock_init(&nilfs->ns_last_segment_lock);
        nilfs->ns_cptree = RB_ROOT;
@@ -307,15 +305,6 @@ int load_nilfs(struct the_nilfs *nilfs, struct nilfs_sb_info *sbi)
        int valid_fs = nilfs_valid_fs(nilfs);
        int err;
 
-       if (nilfs_loaded(nilfs)) {
-               if (valid_fs ||
-                   ((s_flags & MS_RDONLY) && nilfs_test_opt(sbi, NORECOVERY)))
-                       return 0;
-               printk(KERN_ERR "NILFS: the filesystem is in an incomplete "
-                      "recovery state.\n");
-               return -EINVAL;
-       }
-
        if (!valid_fs) {
                printk(KERN_WARNING "NILFS warning: mounting unchecked fs\n");
                if (s_flags & MS_RDONLY) {
@@ -632,12 +621,7 @@ static int nilfs_load_super_block(struct the_nilfs *nilfs,
  *
  * init_nilfs() performs common initialization per block device (e.g.
  * reading the super block, getting disk layout information, initializing
- * shared fields in the_nilfs). It takes on some portion of the jobs
- * typically done by a fill_super() routine. This division arises from
- * the nature that multiple NILFS instances may be simultaneously
- * mounted on a device.
- * For multiple mounts on the same device, only the first mount
- * invokes these tasks.
+ * shared fields in the_nilfs).
  *
  * Return Value: On success, 0 is returned. On error, a negative error
  * code is returned.
@@ -651,27 +635,6 @@ int init_nilfs(struct the_nilfs *nilfs, struct nilfs_sb_info *sbi, char *data)
        int err;
 
        down_write(&nilfs->ns_sem);
-       if (nilfs_init(nilfs)) {
-               /* Load values from existing the_nilfs */
-               sbp = nilfs->ns_sbp[0];
-               err = nilfs_store_magic_and_option(sb, sbp, data);
-               if (err)
-                       goto out;
-
-               err = nilfs_check_feature_compatibility(sb, sbp);
-               if (err)
-                       goto out;
-
-               blocksize = BLOCK_SIZE << le32_to_cpu(sbp->s_log_block_size);
-               if (sb->s_blocksize != blocksize &&
-                   !sb_set_blocksize(sb, blocksize)) {
-                       printk(KERN_ERR "NILFS: blocksize %d unfit to device\n",
-                              blocksize);
-                       err = -EINVAL;
-               }
-               sb->s_maxbytes = nilfs_max_size(sb->s_blocksize_bits);
-               goto out;
-       }
 
        blocksize = sb_min_blocksize(sb, NILFS_MIN_BLOCK_SIZE);
        if (!blocksize) {
@@ -901,56 +864,6 @@ void nilfs_put_root(struct nilfs_root *root)
        }
 }
 
-/**
- * nilfs_find_sbinfo - find existing nilfs_sb_info structure
- * @nilfs: nilfs object
- * @rw_mount: mount type (non-zero value for read/write mount)
- * @cno: checkpoint number (zero for read-only mount)
- *
- * nilfs_find_sbinfo() returns the nilfs_sb_info structure which
- * @rw_mount and @cno (in case of snapshots) matched.  If no instance
- * was found, NULL is returned.  Although the super block instance can
- * be unmounted after this function returns, the nilfs_sb_info struct
- * is kept on memory until nilfs_put_sbinfo() is called.
- */
-struct nilfs_sb_info *nilfs_find_sbinfo(struct the_nilfs *nilfs,
-                                       int rw_mount, __u64 cno)
-{
-       struct nilfs_sb_info *sbi;
-
-       down_read(&nilfs->ns_super_sem);
-       /*
-        * The SNAPSHOT flag and sb->s_flags are supposed to be
-        * protected with nilfs->ns_super_sem.
-        */
-       sbi = nilfs->ns_current;
-       if (rw_mount) {
-               if (sbi && !(sbi->s_super->s_flags & MS_RDONLY))
-                       goto found; /* read/write mount */
-               else
-                       goto out;
-       } else if (cno == 0) {
-               if (sbi && (sbi->s_super->s_flags & MS_RDONLY))
-                       goto found; /* read-only mount */
-               else
-                       goto out;
-       }
-
-       list_for_each_entry(sbi, &nilfs->ns_supers, s_list) {
-               if (nilfs_test_opt(sbi, SNAPSHOT) &&
-                   sbi->s_snapshot_cno == cno)
-                       goto found; /* snapshot mount */
-       }
- out:
-       up_read(&nilfs->ns_super_sem);
-       return NULL;
-
- found:
-       atomic_inc(&sbi->s_count);
-       up_read(&nilfs->ns_super_sem);
-       return sbi;
-}
-
 int nilfs_checkpoint_is_mounted(struct the_nilfs *nilfs, __u64 cno,
                                int snapshot_mount)
 {

diff --git a/fs/nilfs2/the_nilfs.h b/fs/nilfs2/the_nilfs.h
index 0afede6..7b43693 100644 (file)
--- a/fs/nilfs2/the_nilfs.h
+++ b/fs/nilfs2/the_nilfs.h
@@ -52,16 +52,13 @@ enum {
  * @ns_bdi: backing dev info
  * @ns_writer: back pointer to writable nilfs_sb_info
  * @ns_sem: semaphore for shared states
- * @ns_super_sem: semaphore for global operations across super block instances
  * @ns_mount_mutex: mutex protecting mount process of nilfs
  * @ns_writer_sem: semaphore protecting ns_writer attach/detach
- * @ns_current: back pointer to current mount
  * @ns_sbh: buffer heads of on-disk super blocks
  * @ns_sbp: pointers to super block data
  * @ns_sbwtime: previous write time of super block
  * @ns_sbwcount: write count of super block
  * @ns_sbsize: size of valid data in super block
- * @ns_supers: list of nilfs super block structs
  * @ns_seg_seq: segment sequence counter
  * @ns_segnum: index number of the latest full segment.
  * @ns_nextnum: index number of the full segment index to be used next
@@ -104,16 +101,9 @@ struct the_nilfs {
        struct backing_dev_info *ns_bdi;
        struct nilfs_sb_info   *ns_writer;
        struct rw_semaphore     ns_sem;
-       struct rw_semaphore     ns_super_sem;
        struct mutex            ns_mount_mutex;
        struct rw_semaphore     ns_writer_sem;
 
-       /*
-        * components protected by ns_super_sem
-        */
-       struct nilfs_sb_info   *ns_current;
-       struct list_head        ns_supers;
-
        /*
         * used for
         * - loading the latest checkpoint exclusively.
@@ -294,12 +284,6 @@ nilfs_detach_writer(struct the_nilfs *nilfs, struct nilfs_sb_info *sbi)
        up_write(&nilfs->ns_writer_sem);
 }
 
-static inline void nilfs_put_sbinfo(struct nilfs_sb_info *sbi)
-{
-       if (atomic_dec_and_test(&sbi->s_count))
-               kfree(sbi);
-}
-
 static inline int nilfs_valid_fs(struct the_nilfs *nilfs)
 {
        unsigned valid_fs;