sysfs: Wrap __compat_only_sysfs_link_entry_to_kobj function to change the symlink name

The __compat_only_sysfs_link_entry_to_kobj function creates a symlink
to a kobject but doesn't provide an option to change the symlink file
name.

This patch adds a wrapper function compat_only_sysfs_link_entry_to_kobj
that extends the __compat_only_sysfs_link_entry_to_kobj functionality
which allows function caller to customize the symlink name.
Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
[mpe: Fix compile error when CONFIG_SYSFS=n]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20191211160910.21656-3-sourabhjain@linux.ibm.com

fs/sysfs/group.c

@@ -424,6 +424,25 @@ EXPORT_SYMBOL_GPL(sysfs_remove_link_from_group);
 int __compat_only_sysfs_link_entry_to_kobj(struct kobject *kobj,
 				      struct kobject *target_kobj,
 				      const char *target_name)
+{
+	return compat_only_sysfs_link_entry_to_kobj(kobj, target_kobj,
+						    target_name, NULL);
+}
+EXPORT_SYMBOL_GPL(__compat_only_sysfs_link_entry_to_kobj);
+
+/**
+ * compat_only_sysfs_link_entry_to_kobj - add a symlink to a kobject pointing
+ * to a group or an attribute
+ * @kobj:		The kobject containing the group.
+ * @target_kobj:	The target kobject.
+ * @target_name:	The name of the target group or attribute.
+ * @symlink_name:	The name of the symlink file (target_name will be
+ *			considered if symlink_name is NULL).
+ */
+int compat_only_sysfs_link_entry_to_kobj(struct kobject *kobj,
+					 struct kobject *target_kobj,
+					 const char *target_name,
+					 const char *symlink_name)
 {
 	struct kernfs_node *target;
 	struct kernfs_node *entry;
@@ -448,12 +467,15 @@ int __compat_only_sysfs_link_entry_to_kobj(struct kobject *kobj,
 		return -ENOENT;
 	}
 
-	link = kernfs_create_link(kobj->sd, target_name, entry);
+	if (!symlink_name)
+		symlink_name = target_name;
+
+	link = kernfs_create_link(kobj->sd, symlink_name, entry);
 	if (PTR_ERR(link) == -EEXIST)
-		sysfs_warn_dup(kobj->sd, target_name);
+		sysfs_warn_dup(kobj->sd, symlink_name);
 
 	kernfs_put(entry);
 	kernfs_put(target);
 	return PTR_ERR_OR_ZERO(link);
 }
-EXPORT_SYMBOL_GPL(__compat_only_sysfs_link_entry_to_kobj);
+EXPORT_SYMBOL_GPL(compat_only_sysfs_link_entry_to_kobj);

include/linux/sysfs.h

@@ -300,6 +300,10 @@ void sysfs_remove_link_from_group(struct kobject *kobj, const char *group_name,
 int __compat_only_sysfs_link_entry_to_kobj(struct kobject *kobj,
 				      struct kobject *target_kobj,
 				      const char *target_name);
+int compat_only_sysfs_link_entry_to_kobj(struct kobject *kobj,
+					 struct kobject *target_kobj,
+					 const char *target_name,
+					 const char *symlink_name);
 
 void sysfs_notify(struct kobject *kobj, const char *dir, const char *attr);
 
@@ -508,6 +512,14 @@ static inline int __compat_only_sysfs_link_entry_to_kobj(
 	return 0;
 }
 
+static inline int compat_only_sysfs_link_entry_to_kobj(struct kobject *kobj,
+						       struct kobject *target_kobj,
+						       const char *target_name,
+						       const char *symlink_name)
+{
+	return 0;
+}
+
 static inline void sysfs_notify(struct kobject *kobj, const char *dir,
 				const char *attr)
 {