1Sysfs tagging 2------------- 3 4(Taken almost verbatim from Eric Biederman's netns tagging patch 5commit msg) 6 7The problem. Network devices show up in sysfs and with the network 8namespace active multiple devices with the same name can show up in 9the same directory, ouch! 10 11To avoid that problem and allow existing applications in network 12namespaces to see the same interface that is currently presented in 13sysfs, sysfs now has tagging directory support. 14 15By using the network namespace pointers as tags to separate out the 16the sysfs directory entries we ensure that we don't have conflicts 17in the directories and applications only see a limited set of 18the network devices. 19 20Each sysfs directory entry may be tagged with zero or one 21namespaces. A sysfs_dirent is augmented with a void *s_ns. If a 22directory entry is tagged, then sysfs_dirent->s_flags will have a 23flag between KOBJ_NS_TYPE_NONE and KOBJ_NS_TYPES, and s_ns will 24point to the namespace to which it belongs. 25 26Each sysfs superblock's sysfs_super_info contains an array void 27*ns[KOBJ_NS_TYPES]. When a task in a tagging namespace 28kobj_nstype first mounts sysfs, a new superblock is created. It 29will be differentiated from other sysfs mounts by having its 30s_fs_info->ns[kobj_nstype] set to the new namespace. Note that 31through bind mounting and mounts propagation, a task can easily view 32the contents of other namespaces' sysfs mounts. Therefore, when a 33namespace exits, it will call kobj_ns_exit() to invalidate any 34sysfs_dirent->s_ns pointers pointing to it. 35 36Users of this interface: 37- define a type in the kobj_ns_type enumeration. 38- call kobj_ns_type_register() with its kobj_ns_type_operations which has 39 - current_ns() which returns current's namespace 40 - netlink_ns() which returns a socket's namespace 41 - initial_ns() which returns the initial namesapce 42- call kobj_ns_exit() when an individual tag is no longer valid 43