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Subject[RFC 1/5] fs: add iterate_supers_reverse()
Date
There are use cases where we wish to traverse the superblock list
in reverse order. This particular implementation will also enable
to capture errors.

Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
---
fs/super.c | 43 +++++++++++++++++++++++++++++++++++++++++++
include/linux/fs.h | 1 +
2 files changed, 44 insertions(+)

diff --git a/fs/super.c b/fs/super.c
index 02da00410de8..d45e92d9a38f 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -609,6 +609,49 @@ void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
spin_unlock(&sb_lock);
}

+/**
+ * iterate_supers_reverse - call function for active superblocks in reverse
+ * @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. Returns if
+ * an error occurred.
+ */
+int iterate_supers_reverse(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_read(&sb->s_umount);
+ if (sb->s_root && (sb->s_flags & SB_BORN)) {
+ error = f(sb, arg);
+ if (error) {
+ spin_lock(&sb_lock);
+ break;
+ }
+ }
+ 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);
+
+ 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 46796b2f956b..cd084792cf39 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3097,6 +3097,7 @@ 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_reverse(int (*)(struct super_block *, void *), void *);
extern void iterate_supers_type(struct file_system_type *,
void (*)(struct super_block *, void *), void *);

--
2.14.0
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