linux-kernel - [PATCH 3.16.y-ckt 136/185] sysfs: Add support for permanently empty directories to serve as mount points.

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Date:	Wed, 15 Jul 2015 10:12:11 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 136/185] sysfs: Add support for permanently empty directories to serve as mount points.

3.16.7-ckt15 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: "Eric W. Biederman" <ebiederm@...ssion.com>

commit 87d2846fcf88113fae2341da1ca9a71f0d916f2c upstream.

Add two functions sysfs_create_mount_point and
sysfs_remove_mount_point that hang a permanently empty directory off
of a kobject or remove a permanently emptpy directory hanging from a
kobject.  Export these new functions so modular filesystems can use
them.

Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 fs/sysfs/dir.c        | 34 ++++++++++++++++++++++++++++++++++
 include/linux/sysfs.h | 15 +++++++++++++++
 2 files changed, 49 insertions(+)

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 0b45ff42f374..94374e435025 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -121,3 +121,37 @@ int sysfs_move_dir_ns(struct kobject *kobj, struct kobject *new_parent_kobj,
 
 	return kernfs_rename_ns(kn, new_parent, kn->name, new_ns);
 }
+
+/**
+ * sysfs_create_mount_point - create an always empty directory
+ * @parent_kobj:  kobject that will contain this always empty directory
+ * @name: The name of the always empty directory to add
+ */
+int sysfs_create_mount_point(struct kobject *parent_kobj, const char *name)
+{
+	struct kernfs_node *kn, *parent = parent_kobj->sd;
+
+	kn = kernfs_create_empty_dir(parent, name);
+	if (IS_ERR(kn)) {
+		if (PTR_ERR(kn) == -EEXIST)
+			sysfs_warn_dup(parent, name);
+		return PTR_ERR(kn);
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(sysfs_create_mount_point);
+
+/**
+ *	sysfs_remove_mount_point - remove an always empty directory.
+ *	@parent_kobj: kobject that will contain this always empty directory
+ *	@name: The name of the always empty directory to remove
+ *
+ */
+void sysfs_remove_mount_point(struct kobject *parent_kobj, const char *name)
+{
+	struct kernfs_node *parent = parent_kobj->sd;
+
+	kernfs_remove_by_name_ns(parent, name, NULL);
+}
+EXPORT_SYMBOL_GPL(sysfs_remove_mount_point);
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index f97d0dbb59fa..8ce4e648efc1 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -186,6 +186,10 @@ int __must_check sysfs_rename_dir_ns(struct kobject *kobj, const char *new_name,
 int __must_check sysfs_move_dir_ns(struct kobject *kobj,
 				   struct kobject *new_parent_kobj,
 				   const void *new_ns);
+int __must_check sysfs_create_mount_point(struct kobject *parent_kobj,
+					  const char *name);
+void sysfs_remove_mount_point(struct kobject *parent_kobj,
+			      const char *name);
 
 int __must_check sysfs_create_file_ns(struct kobject *kobj,
 				      const struct attribute *attr,
@@ -274,6 +278,17 @@ static inline int sysfs_move_dir_ns(struct kobject *kobj,
 	return 0;
 }
 
+static inline int sysfs_create_mount_point(struct kobject *parent_kobj,
+					   const char *name)
+{
+	return 0;
+}
+
+static inline void sysfs_remove_mount_point(struct kobject *parent_kobj,
+					    const char *name)
+{
+}
+
 static inline int sysfs_create_file_ns(struct kobject *kobj,
 				       const struct attribute *attr,
 				       const void *ns)
--
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