[PATCH 3/4] sysfs: Implement sysfs_delete_link and sysfs_rename_link

[ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org (Eric W. Biederman)]

When removing a symlink sysfs_remove_link does not provide enough
information to figure out which shadow 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 shadow 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-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
---
 fs/sysfs/symlink.c    |   31 +++++++++++++++++++++++++++++++
 include/linux/sysfs.h |   18 ++++++++++++++++++
 2 files changed, 49 insertions(+), 0 deletions(-)

diff --git a/fs/sysfs/symlink.c b/fs/sysfs/symlink.c
index e52d3ef..62b0aeb 100644
--- a/fs/sysfs/symlink.c
+++ b/fs/sysfs/symlink.c
@@ -126,6 +126,21 @@ addrm_finish:
 
 
 /**
+ *	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 shadow 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.
@@ -136,6 +151,22 @@ void sysfs_remove_link(struct kobject * kobj, const char * name)
 	sysfs_hash_and_remove(kobj, kobj->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 7cda047..e195cb5 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -127,6 +127,13 @@ sysfs_create_link(struct kobject * kobj, struct kobject * target, const char * n
 extern void
 sysfs_remove_link(struct kobject *, const char * name);
 
+extern int
+sysfs_rename_link(struct kobject *kobj, struct kobject *target,
+			const char *old_name, const char *new_name);
+
+extern void
+sysfs_delete_link(struct kobject *dir, struct kobject *targ, const char *name);
+
 int __must_check sysfs_create_bin_file(struct kobject *kobj,
 					struct bin_attribute *attr);
 void sysfs_remove_bin_file(struct kobject *kobj, struct bin_attribute *attr);
@@ -202,6 +209,17 @@ static inline void sysfs_remove_link(struct kobject * k, 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_bin_file(struct kobject * k, struct bin_attribute * a)
 {
-- 
1.5.1.1.181.g2de0