Based on kernel version 3.9. Page generated on 2013-05-02 23:06 EST.
1 Sysfs tagging 2 ------------- 3 4 (Taken almost verbatim from Eric Biederman's netns tagging patch 5 commit msg) 6 7 The problem. Network devices show up in sysfs and with the network 8 namespace active multiple devices with the same name can show up in 9 the same directory, ouch! 10 11 To avoid that problem and allow existing applications in network 12 namespaces to see the same interface that is currently presented in 13 sysfs, sysfs now has tagging directory support. 14 15 By using the network namespace pointers as tags to separate out the 16 the sysfs directory entries we ensure that we don't have conflicts 17 in the directories and applications only see a limited set of 18 the network devices. 19 20 Each sysfs directory entry may be tagged with zero or one 21 namespaces. A sysfs_dirent is augmented with a void *s_ns. If a 22 directory entry is tagged, then sysfs_dirent->s_flags will have a 23 flag between KOBJ_NS_TYPE_NONE and KOBJ_NS_TYPES, and s_ns will 24 point to the namespace to which it belongs. 25 26 Each sysfs superblock's sysfs_super_info contains an array void 27 *ns[KOBJ_NS_TYPES]. When a a task in a tagging namespace 28 kobj_nstype first mounts sysfs, a new superblock is created. It 29 will be differentiated from other sysfs mounts by having its 30 s_fs_info->ns[kobj_nstype] set to the new namespace. Note that 31 through bind mounting and mounts propagation, a task can easily view 32 the contents of other namespaces' sysfs mounts. Therefore, when a 33 namespace exits, it will call kobj_ns_exit() to invalidate any 34 sysfs_dirent->s_ns pointers pointing to it. 35 36 Users 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namespace 41 - initial_ns() which returns the initial namesapce 42 - call kobj_ns_exit() when an individual tag is no longer valid