Re: [PATCH 05/11] fs: add iterate_supers_excl() and iterate_supers_reverse_excl()

---
 fs/super.c         | 91 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/fs.h |  2 ++
 2 files changed, 93 insertions(+)

diff --git a/fs/super.c b/fs/super.c
index a63513d187e8..885711c1d35b 100644
--- a/fs/super.c
+++ b/fs/super.c

@@ -605,6 +605,97 @@ void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
 	spin_unlock(&sb_lock);
 }
 
+/**
+ *	iterate_supers_excl - exclusively call func for all active superblocks
+ *	@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. Returns 0 unless an error
+ *	occurred on calling the function on any superblock.
+ */
+int iterate_supers_excl(int (*f)(struct super_block *, void *), void *arg)
+{
+	struct super_block *sb, *p = NULL;
+	int error = 0;
+
+	spin_lock(&sb_lock);
+	list_for_each_entry(sb, &super_blocks, s_list) {
+		if (hlist_unhashed(&sb->s_instances))
+			continue;
+		sb->s_count++;
+		spin_unlock(&sb_lock);
+
+		down_write(&sb->s_umount);
+		if (sb->s_root && (sb->s_flags & SB_BORN)) {
+			error = f(sb, arg);
+			if (error) {
+				up_write(&sb->s_umount);
+				spin_lock(&sb_lock);
+				__put_super(sb);
+				break;
+			}
+		}
+		up_write(&sb->s_umount);
+
+		spin_lock(&sb_lock);
+		if (p)
+			__put_super(p);
+		p = sb;
+	}
+	if (p)
+		__put_super(p);
+	spin_unlock(&sb_lock);
+
+	return error;
+}
+
+/**
+ *	iterate_supers_reverse_excl - exclusively calls func in reverse order
+ *	@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, in reverse order, and holding
+ *	the s_umount write lock. Returns if an error occurred.
+ */
+int iterate_supers_reverse_excl(int (*f)(struct super_block *, void *),
+					 void *arg)
+{
+	struct super_block *sb, *p = NULL;
+	int error = 0;
+
+	spin_lock(&sb_lock);
+	list_for_each_entry_reverse(sb, &super_blocks, s_list) {
+		if (hlist_unhashed(&sb->s_instances))
+			continue;
+		sb->s_count++;
+		spin_unlock(&sb_lock);
+
+		down_write(&sb->s_umount);
+		if (sb->s_root && (sb->s_flags & SB_BORN)) {
+			error = f(sb, arg);
+			if (error) {
+				up_write(&sb->s_umount);
+				spin_lock(&sb_lock);
+				__put_super(sb);
+				break;
+			}
+		}
+		up_write(&sb->s_umount);
+
+		spin_lock(&sb_lock);
+		if (p)
+			__put_super(p);
+		p = sb;
+	}
+	if (p)
+		__put_super(p);
+	spin_unlock(&sb_lock);
+
+	return error;
+}
+
 /**
  *	iterate_supers_type - call function for superblocks of given type
  *	@type: fs type

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 107725b20fad..fe90b6542697 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h

@@ -3164,6 +3164,8 @@ extern struct super_block *get_active_super(struct block_device *bdev);
 extern void drop_super(struct super_block *sb);
 extern void drop_super_exclusive(struct super_block *sb);
 extern void iterate_supers(void (*)(struct super_block *, void *), void *);
+extern int iterate_supers_excl(int (*f)(struct super_block *, void *), void *arg);
+extern int iterate_supers_reverse_excl(int (*)(struct super_block *, void *), void *);
 extern void iterate_supers_type(struct file_system_type *,
 			        void (*)(struct super_block *, void *), void *);
 

-- 
2.15.0