sysfs: Functions for adding/removing symlinks to/from attribute groups

The most convenient way to expose ACPI power resources lists of a
device is to put symbolic links to sysfs directories representing
those resources into special attribute groups in the device's sysfs
directory.  For this purpose, it is necessary to be able to add
symbolic links to attribute groups.

For this reason, add sysfs helper functions for adding/removing
symbolic links to/from attribute groups, sysfs_add_link_to_group()
and sysfs_remove_link_from_group(), respectively.

This change set includes a build fix from David Rientjes.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 42 insertions, 0 deletions

diff --git a/fs/sysfs/group.c b/fs/sysfs/group.c
index 2df555c66d57..aec3d5c98c94 100644
--- a/fs/sysfs/group.c
+++ b/fs/sysfs/group.c
@@ -205,6 +205,48 @@ void sysfs_unmerge_group(struct kobject *kobj,
 }
 EXPORT_SYMBOL_GPL(sysfs_unmerge_group);
 
+/**
+ * sysfs_add_link_to_group - add a symlink to an attribute group.
+ * @kobj:       The kobject containing the group.
+ * @group_name: The name of the group.
+ * @target:     The target kobject of the symlink to create.
+ * @link_name:  The name of the symlink to create.
+ */
+int sysfs_add_link_to_group(struct kobject *kobj, const char *group_name,
+                            struct kobject *target, const char *link_name)
+{
+        struct sysfs_dirent *dir_sd;
+        int error = 0;
+
+        dir_sd = sysfs_get_dirent(kobj->sd, NULL, group_name);
+        if (!dir_sd)
+                return -ENOENT;
+
+        error = sysfs_create_link_sd(dir_sd, target, link_name);
+        sysfs_put(dir_sd);
+
+        return error;
+}
+EXPORT_SYMBOL_GPL(sysfs_add_link_to_group);
+
+/**
+ * sysfs_remove_link_from_group - remove a symlink from an attribute group.
+ * @kobj:       The kobject containing the group.
+ * @group_name: The name of the group.
+ * @link_name:  The name of the symlink to remove.
+ */
+void sysfs_remove_link_from_group(struct kobject *kobj, const char *group_name,
+                                  const char *link_name)
+{
+        struct sysfs_dirent *dir_sd;
+
+        dir_sd = sysfs_get_dirent(kobj->sd, NULL, group_name);
+        if (dir_sd) {
+                sysfs_hash_and_remove(dir_sd, NULL, link_name);
+                sysfs_put(dir_sd);
+        }
+}
+EXPORT_SYMBOL_GPL(sysfs_remove_link_from_group);
 
 EXPORT_SYMBOL_GPL(sysfs_create_group);
 EXPORT_SYMBOL_GPL(sysfs_update_group);