1 files changed, 50 insertions, 0 deletions

diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
index 45dbf6a61744..221953bfc859 100644
--- a/fs/nilfs2/the_nilfs.c
+++ b/fs/nilfs2/the_nilfs.c
@@ -664,6 +664,56 @@ int nilfs_near_disk_full(struct the_nilfs *nilfs)
         return ret;
 }
 
+/**
+ * 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_sem);
+        /*
+         * The SNAPSHOT flag and sb->s_flags are supposed to be
+         * protected with nilfs->ns_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_sem);
+        return NULL;
+
+ found:
+        atomic_inc(&sbi->s_count);
+        up_read(&nilfs->ns_sem);
+        return sbi;
+}
+
 int nilfs_checkpoint_is_mounted(struct the_nilfs *nilfs, __u64 cno,
                                 int snapshot_mount)
 {