[PATCH] sysfs: do not create empty directories if no attributes are present

[Greg Kroah-Hartman]

When creating an attribute group, if it is named a subdirectory is
created and the sysfs files are placed into that subdirectory.  If no
files are created, normally the directory would still be present, but it
would be empty.  Clean this up by removing the directory if no files
were successfully created in the group at all.

Co-developed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Co-developed-by: Alistair Francis <alistair.francis@xxxxxxx>
Signed-off-by: Alistair Francis <alistair.francis@xxxxxxx>
---
 fs/sysfs/file.c  | 14 ++++++++++--
 fs/sysfs/group.c | 56 ++++++++++++++++++++++++++++++++++++------------
 2 files changed, 54 insertions(+), 16 deletions(-)

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index a12ac0356c69..7aab6c09662c 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -391,8 +391,18 @@ int sysfs_add_file_to_group(struct kobject *kobj,
 		kernfs_get(parent);
 	}
 
-	if (!parent)
-		return -ENOENT;
+	if (!parent) {
+		parent = kernfs_create_dir_ns(kobj->sd, group,
+					  S_IRWXU | S_IRUGO | S_IXUGO,
+					  uid, gid, kobj, NULL);
+		if (IS_ERR(parent)) {
+			if (PTR_ERR(parent) == -EEXIST)
+				sysfs_warn_dup(kobj->sd, group);
+			return PTR_ERR(parent);
+		}
+
+		kernfs_get(parent);
+	}
 
 	kobject_get_ownership(kobj, &uid, &gid);
 	error = sysfs_add_file_mode_ns(parent, attr, attr->mode, uid, gid,
diff --git a/fs/sysfs/group.c b/fs/sysfs/group.c
index 138676463336..013fa333cd3c 100644
--- a/fs/sysfs/group.c
+++ b/fs/sysfs/group.c
@@ -31,12 +31,14 @@ static void remove_files(struct kernfs_node *parent,
 			kernfs_remove_by_name(parent, (*bin_attr)->attr.name);
 }
 
+/* returns -ERROR if error, or >= 0 for number of files actually created */
 static int create_files(struct kernfs_node *parent, struct kobject *kobj,
 			kuid_t uid, kgid_t gid,
 			const struct attribute_group *grp, int update)
 {
 	struct attribute *const *attr;
 	struct bin_attribute *const *bin_attr;
+	int files_created = 0;
 	int error = 0, i;
 
 	if (grp->attrs) {
@@ -65,6 +67,8 @@ static int create_files(struct kernfs_node *parent, struct kobject *kobj,
 						       gid, NULL);
 			if (unlikely(error))
 				break;
+
+			files_created++;
 		}
 		if (error) {
 			remove_files(parent, grp);
@@ -95,12 +99,15 @@ static int create_files(struct kernfs_node *parent, struct kobject *kobj,
 							   NULL);
 			if (error)
 				break;
+			files_created++;
 		}
 		if (error)
 			remove_files(parent, grp);
 	}
 exit:
-	return error;
+	if (error)
+		return error;
+	return files_created;
 }
 
 
@@ -130,9 +137,14 @@ static int internal_create_group(struct kobject *kobj, int update,
 		if (update) {
 			kn = kernfs_find_and_get(kobj->sd, grp->name);
 			if (!kn) {
-				pr_warn("Can't update unknown attr grp name: %s/%s\n",
-					kobj->name, grp->name);
-				return -EINVAL;
+				kn = kernfs_create_dir_ns(kobj->sd, grp->name,
+							  S_IRWXU | S_IRUGO | S_IXUGO,
+							  uid, gid, kobj, NULL);
+				if (IS_ERR(kn)) {
+					if (PTR_ERR(kn) == -EEXIST)
+						sysfs_warn_dup(kobj->sd, grp->name);
+					return PTR_ERR(kn);
+				}
 			}
 		} else {
 			kn = kernfs_create_dir_ns(kobj->sd, grp->name,
@@ -150,11 +162,18 @@ static int internal_create_group(struct kobject *kobj, int update,
 
 	kernfs_get(kn);
 	error = create_files(kn, kobj, uid, gid, grp, update);
-	if (error) {
+	if (error <= 0) {
+		/*
+		 * If an error happened _OR_ if no files were created in the
+		 * attribute group, and we have a name for this group, delete
+		 * the name so there's not an empty directory.
+		 */
 		if (grp->name)
 			kernfs_remove(kn);
+	} else {
+		error = 0;
+		kernfs_put(kn);
 	}
-	kernfs_put(kn);
 
 	if (grp->name && update)
 		kernfs_put(kn);
@@ -318,13 +337,12 @@ void sysfs_remove_groups(struct kobject *kobj,
 EXPORT_SYMBOL_GPL(sysfs_remove_groups);
 
 /**
- * sysfs_merge_group - merge files into a pre-existing attribute group.
+ * sysfs_merge_group - merge files into a attribute group.
  * @kobj:	The kobject containing the group.
  * @grp:	The files to create and the attribute group they belong to.
  *
- * This function returns an error if the group doesn't exist or any of the
- * files already exist in that group, in which case none of the new files
- * are created.
+ * This function returns an error if any of the files already exist in
+ * that group, in which case none of the new files are created.
  */
 int sysfs_merge_group(struct kobject *kobj,
 		       const struct attribute_group *grp)
@@ -336,12 +354,22 @@ int sysfs_merge_group(struct kobject *kobj,
 	struct attribute *const *attr;
 	int i;
 
-	parent = kernfs_find_and_get(kobj->sd, grp->name);
-	if (!parent)
-		return -ENOENT;
-
 	kobject_get_ownership(kobj, &uid, &gid);
 
+	parent = kernfs_find_and_get(kobj->sd, grp->name);
+	if (!parent) {
+		parent = kernfs_create_dir_ns(kobj->sd, grp->name,
+					  S_IRWXU | S_IRUGO | S_IXUGO,
+					  uid, gid, kobj, NULL);
+		if (IS_ERR(parent)) {
+			if (PTR_ERR(parent) == -EEXIST)
+				sysfs_warn_dup(kobj->sd, grp->name);
+			return PTR_ERR(parent);
+		}
+
+		kernfs_get(parent);
+	}
+
 	for ((i = 0, attr = grp->attrs); *attr && !error; (++i, ++attr))
 		error = sysfs_add_file_mode_ns(parent, *attr, (*attr)->mode,
 					       uid, gid, NULL);
-- 
2.42.0