new helper: iterate_supers_type()

Call the given function for all superblocks of given type.  Function
gets a superblock (with s_umount locked shared) and (void *) argument
supplied by caller of iterator.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 36 insertions, 0 deletions

diff --git a/fs/super.c b/fs/super.c
index ab3d672db0de..444da9579068 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -452,6 +452,42 @@ void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
 }
 
 /**
+ *      iterate_supers_type - call function for superblocks of given type
+ *      @type: fs type
+ *      @f: function to call
+ *      @arg: argument to pass to it
+ *
+ *      Scans the superblock list and calls given function, passing it
+ *      locked superblock and given argument.
+ */
+void iterate_supers_type(struct file_system_type *type,
+        void (*f)(struct super_block *, void *), void *arg)
+{
+        struct super_block *sb, *p = NULL;
+
+        spin_lock(&sb_lock);
+        list_for_each_entry(sb, &type->fs_supers, s_instances) {
+                sb->s_count++;
+                spin_unlock(&sb_lock);
+
+                down_read(&sb->s_umount);
+                if (sb->s_root)
+                        f(sb, arg);
+                up_read(&sb->s_umount);
+
+                spin_lock(&sb_lock);
+                if (p)
+                        __put_super(p);
+                p = sb;
+        }
+        if (p)
+                __put_super(p);
+        spin_unlock(&sb_lock);
+}
+
+EXPORT_SYMBOL(iterate_supers_type);
+
+/**
  *      get_super - get the superblock of a device
  *      @bdev: device to get the superblock for
  *