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authorEric W. Biederman <ebiederm@xmission.com>2015-05-13 16:09:29 -0500
committerEric W. Biederman <ebiederm@xmission.com>2015-07-01 10:36:43 -0500
commitea015218f2f7ace2dad9cedd21ed95bdba2886d7 (patch)
tree9ab4dc58398a5ef08b174871a9cc587680261b65
parentproc: Allow creating permanently empty directories that serve as mount points (diff)
downloadlinux-dev-ea015218f2f7ace2dad9cedd21ed95bdba2886d7.tar.xz
linux-dev-ea015218f2f7ace2dad9cedd21ed95bdba2886d7.zip
kernfs: Add support for always empty directories.
Add a new function kernfs_create_empty_dir that can be used to create directory that can not be modified. Update the code to use make_empty_dir_inode when reporting a permanently empty directory to the vfs. Update the code to not allow adding to permanently empty directories. Cc: stable@vger.kernel.org Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
-rw-r--r--fs/kernfs/dir.c38
-rw-r--r--fs/kernfs/inode.c2
-rw-r--r--include/linux/kernfs.h3
3 files changed, 42 insertions, 1 deletions
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index f131fc23ffc4..47dc636d80ed 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -585,6 +585,9 @@ int kernfs_add_one(struct kernfs_node *kn)
goto out_unlock;
ret = -ENOENT;
+ if (parent->flags & KERNFS_EMPTY_DIR)
+ goto out_unlock;
+
if ((parent->flags & KERNFS_ACTIVATED) && !kernfs_active(parent))
goto out_unlock;
@@ -776,6 +779,38 @@ struct kernfs_node *kernfs_create_dir_ns(struct kernfs_node *parent,
return ERR_PTR(rc);
}
+/**
+ * kernfs_create_empty_dir - create an always empty directory
+ * @parent: parent in which to create a new directory
+ * @name: name of the new directory
+ *
+ * Returns the created node on success, ERR_PTR() value on failure.
+ */
+struct kernfs_node *kernfs_create_empty_dir(struct kernfs_node *parent,
+ const char *name)
+{
+ struct kernfs_node *kn;
+ int rc;
+
+ /* allocate */
+ kn = kernfs_new_node(parent, name, S_IRUGO|S_IXUGO|S_IFDIR, KERNFS_DIR);
+ if (!kn)
+ return ERR_PTR(-ENOMEM);
+
+ kn->flags |= KERNFS_EMPTY_DIR;
+ kn->dir.root = parent->dir.root;
+ kn->ns = NULL;
+ kn->priv = NULL;
+
+ /* link in */
+ rc = kernfs_add_one(kn);
+ if (!rc)
+ return kn;
+
+ kernfs_put(kn);
+ return ERR_PTR(rc);
+}
+
static struct dentry *kernfs_iop_lookup(struct inode *dir,
struct dentry *dentry,
unsigned int flags)
@@ -1247,7 +1282,8 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
mutex_lock(&kernfs_mutex);
error = -ENOENT;
- if (!kernfs_active(kn) || !kernfs_active(new_parent))
+ if (!kernfs_active(kn) || !kernfs_active(new_parent) ||
+ (new_parent->flags & KERNFS_EMPTY_DIR))
goto out;
error = 0;
diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c
index 2da8493a380b..756dd56aaf60 100644
--- a/fs/kernfs/inode.c
+++ b/fs/kernfs/inode.c
@@ -296,6 +296,8 @@ static void kernfs_init_inode(struct kernfs_node *kn, struct inode *inode)
case KERNFS_DIR:
inode->i_op = &kernfs_dir_iops;
inode->i_fop = &kernfs_dir_fops;
+ if (kn->flags & KERNFS_EMPTY_DIR)
+ make_empty_dir_inode(inode);
break;
case KERNFS_FILE:
inode->i_size = kn->attr.size;
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 71ecdab1671b..29d1896c3ba5 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -45,6 +45,7 @@ enum kernfs_node_flag {
KERNFS_LOCKDEP = 0x0100,
KERNFS_SUICIDAL = 0x0400,
KERNFS_SUICIDED = 0x0800,
+ KERNFS_EMPTY_DIR = 0x1000,
};
/* @flags for kernfs_create_root() */
@@ -285,6 +286,8 @@ void kernfs_destroy_root(struct kernfs_root *root);
struct kernfs_node *kernfs_create_dir_ns(struct kernfs_node *parent,
const char *name, umode_t mode,
void *priv, const void *ns);
+struct kernfs_node *kernfs_create_empty_dir(struct kernfs_node *parent,
+ const char *name);
struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
const char *name,
umode_t mode, loff_t size,