linux-kernel - [PATCH 4/9] vfs: introduce clone_private

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Message-Id: <1363184193-1796-5-git-send-email-miklos@szeredi.hu>
Date:	Wed, 13 Mar 2013 15:16:28 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	viro@...IV.linux.org.uk, torvalds@...ux-foundation.org
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	hch@...radead.org, akpm@...ux-foundation.org, apw@...onical.com,
	nbd@...nwrt.org, neilb@...e.de, jordipujolp@...il.com,
	ezk@....cs.sunysb.edu, dhowells@...hat.com,
	sedat.dilek@...glemail.com, hooanon05@...oo.co.jp, mszeredi@...e.cz
Subject: [PATCH 4/9] vfs: introduce clone_private_mount()

From: Miklos Szeredi <mszeredi@...e.cz>

Overlayfs needs a private clone of the mount, so create a function for
this and export to modules.

Signed-off-by: Miklos Szeredi <mszeredi@...e.cz>
---
 fs/namespace.c        |   18 ++++++++++++++++++
 include/linux/mount.h |    3 +++
 2 files changed, 21 insertions(+)

diff --git a/fs/namespace.c b/fs/namespace.c
index 50ca17d..9791b4e 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1399,6 +1399,24 @@ void drop_collected_mounts(struct vfsmount *mnt)
 	release_mounts(&umount_list);
 }
 
+struct vfsmount *clone_private_mount(struct path *path)
+{
+	struct mount *old_mnt = real_mount(path->mnt);
+	struct mount *new_mnt;
+
+	if (IS_MNT_UNBINDABLE(old_mnt))
+		return ERR_PTR(-EINVAL);
+
+	down_read(&namespace_sem);
+	new_mnt = clone_mnt(old_mnt, path->dentry, CL_PRIVATE);
+	up_read(&namespace_sem);
+	if (!new_mnt)
+		return ERR_PTR(-ENOMEM);
+
+	return &new_mnt->mnt;
+}
+EXPORT_SYMBOL_GPL(clone_private_mount);
+
 int iterate_mounts(int (*f)(struct vfsmount *, void *), void *arg,
 		   struct vfsmount *root)
 {
diff --git a/include/linux/mount.h b/include/linux/mount.h
index d7029f4..344a262 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -66,6 +66,9 @@ extern void mnt_pin(struct vfsmount *mnt);
 extern void mnt_unpin(struct vfsmount *mnt);
 extern int __mnt_is_readonly(struct vfsmount *mnt);
 
+struct path;
+extern struct vfsmount *clone_private_mount(struct path *path);
+
 struct file_system_type;
 extern struct vfsmount *vfs_kern_mount(struct file_system_type *type,
 				      int flags, const char *name,
-- 
1.7.10.4

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