[PATCH 3/8] sysfs: Implement sysfs_delete_link and sysfs_rename_link

[ebiederm@xmission.com (Eric W. Biederman)]

When removing a symlink sysfs_remove_link does not provide
enough information to figure out which tagged directory the symlink
falls in.  So I need sysfs_delete_link which is passed the target
of the symlink to delete.

Further half the time when we are removing a symlink the code is
actually renaming the symlink but not doing so explicitly because
we don't have a symlink rename method. So I have added sysfs_rename_link
as well.

Both of these functions now have enough information to find a symlink
in a tagged directory.  The only restriction is that they must be called
before the target kobject is renamed or deleted.  If they are called
later I loose track of which tag the target kobject was marked with
and can no longer find the old symlink to remove it.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Benjamin Thery <benjamin.thery@bull.net>
Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>
Acked-by: Tejun Heo <tj@kernel.org>
---
 fs/sysfs/symlink.c    |   31 +++++++++++++++++++++++++++++++
 include/linux/sysfs.h |   17 +++++++++++++++++
 2 files changed, 48 insertions(+), 0 deletions(-)

diff --git a/fs/sysfs/symlink.c b/fs/sysfs/symlink.c
index 54b2e5f..2a64645 100644
--- a/fs/sysfs/symlink.c
+++ b/fs/sysfs/symlink.c
@@ -105,6 +105,21 @@ int sysfs_create_link_nowarn(struct kobject *kobj, struct kobject *target,
 }
 
 /**
+ *	sysfs_delete_link - remove symlink in object's directory.
+ *	@kobj:	object we're acting for.
+ *	@targ:	object we're pointing to.
+ *	@name:	name of the symlink to remove.
+ *
+ *	Unlike sysfs_remove_link sysfs_delete_link has enough information
+ *	to successfully delete symlinks in tagged directories.
+ */
+void sysfs_delete_link(struct kobject *kobj, struct kobject *targ,
+			const char *name)
+{
+	sysfs_hash_and_remove(targ, kobj->sd, name);
+}
+
+/**
  *	sysfs_remove_link - remove symlink in object's directory.
  *	@kobj:	object we're acting for.
  *	@name:	name of the symlink to remove.
@@ -122,6 +137,22 @@ void sysfs_remove_link(struct kobject * kobj, const char * name)
 	sysfs_hash_and_remove(kobj, parent_sd, name);
 }
 
+/**
+ *	sysfs_rename_link - rename symlink in object's directory.
+ *	@kobj:	object we're acting for.
+ *	@targ:	object we're pointing to.
+ *	@old:	previous name of the symlink.
+ *	@new:	new name of the symlink.
+ *
+ *	A helper function for the common rename symlink idiom.
+ */
+int sysfs_rename_link(struct kobject *kobj, struct kobject *targ,
+			const char *old, const char *new)
+{
+	sysfs_delete_link(kobj, targ, old);
+	return sysfs_create_link(kobj, targ, new);
+}
+
 static int sysfs_get_target_path(struct sysfs_dirent *parent_sd,
 				 struct sysfs_dirent *target_sd, char *path)
 {
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index ba68829..1204d45 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -117,6 +117,12 @@ int __must_check sysfs_create_link_nowarn(struct kobject *kobj,
 					  const char *name);
 void sysfs_remove_link(struct kobject *kobj, const char *name);
 
+int sysfs_rename_link(struct kobject *kobj, struct kobject *target,
+			const char *old_name, const char *new_name);
+
+void sysfs_delete_link(struct kobject *dir, struct kobject *targ,
+			const char *name);
+
 int __must_check sysfs_create_group(struct kobject *kobj,
 				    const struct attribute_group *grp);
 int sysfs_update_group(struct kobject *kobj,
@@ -216,6 +222,17 @@ static inline void sysfs_remove_link(struct kobject *kobj, const char *name)
 {
 }
 
+static inline int sysfs_rename_link(struct kobject *k, struct kobject *t,
+				    const char *old_name, const char *new_name)
+{
+	return 0;
+}
+
+static inline void sysfs_delete_link(struct kobject *k, struct kobject *t,
+				     const char *name)
+{
+}
+
 static inline int sysfs_create_group(struct kobject *kobj,
 				     const struct attribute_group *grp)
 {
-- 
1.5.3.rc6.17.g1911