[RFC PATCH 2/3] libfs: add simple directory iteration function with callback

[James Bottomley <James.Bottomley@HansenPartnership.com>]

The current iterate_dir() infrastructure is somewhat cumbersome to use
from within the kernel.  Introduce a lighter weight
simple_iterate_dir() function that directly iterates the directory and
executes a callback for each positive dentry.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
---
 fs/libfs.c         | 33 +++++++++++++++++++++++++++++++++
 include/linux/fs.h |  2 ++
 2 files changed, 35 insertions(+)

diff --git a/fs/libfs.c b/fs/libfs.c
index 816bfe6c0430..37da5fe25242 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -214,6 +214,39 @@ static void internal_readdir(struct dentry *dentry, struct dentry *cursor,
 	dput(next);
 }
 
+/**
+ * generic_iterate_call - iterate all entries executing @callback
+ *
+ * @dir: directory to iterate over
+ * @data: data passed to callback
+ * @callback: callback to call
+ *
+ * Iterates over all positive dentries that are direct children of
+ * @dir (so doesn't include . and ..) and executes the callback for
+ * each of them.  Note that because there's no struct *mnt, the caller
+ * is responsible for pinning the filesystem.
+ *
+ * If the @callback returns true, the iteration will continue and if
+ * it returns @false, it will stop (note that since the cursor is
+ * destroyed the next invocation will go back to the beginning again).
+ *
+ */
+int simple_iterate_call(struct dentry *dir, void *data,
+			bool (*callback)(void *, struct dentry *))
+{
+	struct dentry *cursor = d_alloc_cursor(dir);
+
+	if (!cursor)
+		return -ENOMEM;
+
+	internal_readdir(dir, cursor, data, true, callback);
+
+	dput(cursor);
+
+	return 0;
+}
+EXPORT_SYMBOL(simple_iterate_call);
+
 static bool dcache_readdir_callback(void *data, struct dentry *entry)
 {
 	struct dir_context *ctx = data;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 2788df98080f..a84896f0b2d1 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3531,6 +3531,8 @@ extern int simple_rename(struct mnt_idmap *, struct inode *,
 			 unsigned int);
 extern void simple_recursive_removal(struct dentry *,
                               void (*callback)(struct dentry *));
+extern int simple_iterate_call(struct dentry *dir, void *data,
+			       bool (*callback)(void *, struct dentry *));
 extern int noop_fsync(struct file *, loff_t, loff_t, int);
 extern ssize_t noop_direct_IO(struct kiocb *iocb, struct iov_iter *iter);
 extern int simple_empty(struct dentry *);
-- 
2.43.0