sysfs, kernfs: introduce kernfs_setattr()

Introduce kernfs setattr interface - kernfs_setattr().

sysfs_sd_setattr() is renamed to __kernfs_setattr() and
kernfs_setattr() is a simple wrapper around it with sysfs_mutex
locking.  sysfs_chmod_file() is updated to get an explicit ref on
kobj->sd and then invoke kernfs_setattr() so that it doesn't have to
use internal interface.

This patch doesn't introduce any behavior differences.

v2: Dummy implementation for !CONFIG_SYSFS updated to return -ENOSYS.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index 5664410..564abd2 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -922,19 +922,16 @@
 	struct iattr newattrs;
 	int rc;
 
-	mutex_lock(&sysfs_mutex);
-
-	rc = -ENOENT;
-	sd = sysfs_find_dirent(kobj->sd, attr->name, NULL);
+	sd = sysfs_get_dirent(kobj->sd, attr->name);
 	if (!sd)
-		goto out;
+		return -ENOENT;
 
 	newattrs.ia_mode = (mode & S_IALLUGO) | (sd->s_mode & ~S_IALLUGO);
 	newattrs.ia_valid = ATTR_MODE;
-	rc = sysfs_sd_setattr(sd, &newattrs);
 
- out:
-	mutex_unlock(&sysfs_mutex);
+	rc = kernfs_setattr(sd, &newattrs);
+
+	sysfs_put(sd);
 	return rc;
 }
 EXPORT_SYMBOL_GPL(sysfs_chmod_file);
diff --git a/fs/sysfs/inode.c b/fs/sysfs/inode.c
index 1750f79..5f7e2af 100644
--- a/fs/sysfs/inode.c
+++ b/fs/sysfs/inode.c
@@ -67,7 +67,7 @@
 	return attrs;
 }
 
-int sysfs_sd_setattr(struct sysfs_dirent *sd, struct iattr *iattr)
+static int __kernfs_setattr(struct sysfs_dirent *sd, const struct iattr *iattr)
 {
 	struct sysfs_inode_attrs *sd_attrs;
 	struct iattr *iattrs;
@@ -102,6 +102,23 @@
 	return 0;
 }
 
+/**
+ * kernfs_setattr - set iattr on a node
+ * @sd: target node
+ * @iattr: iattr to set
+ *
+ * Returns 0 on success, -errno on failure.
+ */
+int kernfs_setattr(struct sysfs_dirent *sd, const struct iattr *iattr)
+{
+	int ret;
+
+	mutex_lock(&sysfs_mutex);
+	ret = __kernfs_setattr(sd, iattr);
+	mutex_unlock(&sysfs_mutex);
+	return ret;
+}
+
 int sysfs_setattr(struct dentry *dentry, struct iattr *iattr)
 {
 	struct inode *inode = dentry->d_inode;
@@ -116,7 +133,7 @@
 	if (error)
 		goto out;
 
-	error = sysfs_sd_setattr(sd, iattr);
+	error = __kernfs_setattr(sd, iattr);
 	if (error)
 		goto out;
 
diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index 8b3fc21..2abccfd 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -207,7 +207,6 @@
  */
 struct inode *sysfs_get_inode(struct super_block *sb, struct sysfs_dirent *sd);
 void sysfs_evict_inode(struct inode *inode);
-int sysfs_sd_setattr(struct sysfs_dirent *sd, struct iattr *iattr);
 int sysfs_permission(struct inode *inode, int mask);
 int sysfs_setattr(struct dentry *dentry, struct iattr *iattr);
 int sysfs_getattr(struct vfsmount *mnt, struct dentry *dentry,