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-Sysfs tagging
--------------
-
-(Taken almost verbatim from Eric Biederman's netns tagging patch
-commit msg)
-
-The problem. Network devices show up in sysfs and with the network
-namespace active multiple devices with the same name can show up in
-the same directory, ouch!
-
-To avoid that problem and allow existing applications in network
-namespaces to see the same interface that is currently presented in
-sysfs, sysfs now has tagging directory support.
-
-By using the network namespace pointers as tags to separate out the
-the sysfs directory entries we ensure that we don't have conflicts
-in the directories and applications only see a limited set of
-the network devices.
-
-Each sysfs directory entry may be tagged with zero or one
-namespaces. A sysfs_dirent is augmented with a void *s_ns. If a
-directory entry is tagged, then sysfs_dirent->s_flags will have a
-flag between KOBJ_NS_TYPE_NONE and KOBJ_NS_TYPES, and s_ns will
-point to the namespace to which it belongs.
-
-Each sysfs superblock's sysfs_super_info contains an array void
-*ns[KOBJ_NS_TYPES]. When a a task in a tagging namespace
-kobj_nstype first mounts sysfs, a new superblock is created. It
-will be differentiated from other sysfs mounts by having its
-s_fs_info->ns[kobj_nstype] set to the new namespace. Note that
-through bind mounting and mounts propagation, a task can easily view
-the contents of other namespaces' sysfs mounts. Therefore, when a
-namespace exits, it will call kobj_ns_exit() to invalidate any
-sysfs_dirent->s_ns pointers pointing to it.
-
-Users of this interface:
-- define a type in the kobj_ns_type enumeration.
-- call kobj_ns_type_register() with its kobj_ns_type_operations which has
- - current_ns() which returns current's namespace
- - netlink_ns() which returns a socket's namespace
- - initial_ns() which returns the initial namesapce
-- call kobj_ns_exit() when an individual tag is no longer valid