sysfs : fix kobject rename with multiple namespaces

To be applied on top of the sysfs per namespace patchset.

Subject: avoid kobject name conflict with different namespaces
From: Daniel Lezcano <dlezcano-NmTC/[email protected]>

The renaming of a kobject will fail if there is another kobject with the same name belonging to another namespace.

This patch makes the kobject lookup in kobject_rename to check if the object exists _and_ belongs to the same namespace.

Signed-off-by Daniel Lezcano <dlezcano-NmTC/[email protected]>

---
 fs/sysfs/dir.c        |   10 ++++++++++
 include/linux/sysfs.h |    7 +++++++
 lib/kobject.c         |    2 +-
 3 files changed, 18 insertions(+), 1 deletion(-)

Index: net-next-2.6/fs/sysfs/dir.c
===================================================================

fs/sysfs/dir.c +9 -0

+{
+	struct sysfs_dirent *sd1 = kobj1->sd;
+	struct sysfs_dirent *sd2 = kobj2->sd;
+	const void *tag1 = sysfs_dirent_tag(sd1);
+	const void *tag2 = sysfs_dirent_tag(sd2);
+
+	return tag1 != tag2;
+}
+
 int sysfs_rename_dir(struct kobject * kobj, const char *new_name)
 {
 	struct sysfs_dirent *sd = kobj->sd;

Index: net-next-2.6/include/linux/sysfs.h
===================================================================

include/linux/sysfs.h +7 -0

@@ -95,6 +95,8 @@ int sysfs_schedule_callback(struct kobje
 
 int __must_check sysfs_create_dir(struct kobject *kobj);
 void sysfs_remove_dir(struct kobject *kobj);
+int sysfs_tag_cmp(struct kobject * kobj1, struct kobject *kobj2);
+
 int __must_check sysfs_rename_dir(struct kobject *kobj, const char *new_name);
 int __must_check sysfs_move_dir(struct kobject *kobj,
 				struct kobject *new_parent_kobj);

@@ -152,6 +154,11 @@ static inline void sysfs_remove_dir(stru
 	;
 }
 
+static inline int sysfs_tag_cmp(struct kobject * kobj1, struct kobject *kobj2)
+{
+	return 0;
+}
+
 static inline int sysfs_rename_dir(struct kobject *kobj, const char *new_name)
 {
 	return 0;

Index: net-next-2.6/lib/kobject.c
===================================================================

lib/kobject.c +1 -1

@@ -418,7 +418,7 @@ int kobject_rename(struct kobject *kobj,
 	if (kobj->kset) {
 		struct kobject *temp_kobj;
 		temp_kobj = kset_find_obj(kobj->kset, new_name);
-		if (temp_kobj) {
+		if (temp_kobj && !sysfs_tag_cmp(temp_kobj, kobj)) {
 			printk(KERN_WARNING "kobject '%s' cannot be renamed "
 			       "to '%s' as '%s' is already in existence.\n",
 			       kobject_name(kobj), new_name, new_name);

The patch looks good to me, except I'd really rename this to 'sysfs_tag_eq'. Calling it 'cmp', returning 't1!=t2', then checking for !sysfs_tag_cmp really increases the amount of thinking i have to do to make sure everything is koshepillager :)

Maybe it's just me.