sysfs-tagging.rst (1947B)
1.. SPDX-License-Identifier: GPL-2.0 2 3============= 4Sysfs tagging 5============= 6 7(Taken almost verbatim from Eric Biederman's netns tagging patch 8commit msg) 9 10The problem. Network devices show up in sysfs and with the network 11namespace active multiple devices with the same name can show up in 12the same directory, ouch! 13 14To avoid that problem and allow existing applications in network 15namespaces to see the same interface that is currently presented in 16sysfs, sysfs now has tagging directory support. 17 18By using the network namespace pointers as tags to separate out 19the sysfs directory entries we ensure that we don't have conflicts 20in the directories and applications only see a limited set of 21the network devices. 22 23Each sysfs directory entry may be tagged with a namespace via the 24``void *ns member`` of its ``kernfs_node``. If a directory entry is tagged, 25then ``kernfs_node->flags`` will have a flag between KOBJ_NS_TYPE_NONE 26and KOBJ_NS_TYPES, and ns will point to the namespace to which it 27belongs. 28 29Each sysfs superblock's kernfs_super_info contains an array 30``void *ns[KOBJ_NS_TYPES]``. When a task in a tagging namespace 31kobj_nstype first mounts sysfs, a new superblock is created. It 32will be differentiated from other sysfs mounts by having its 33``s_fs_info->ns[kobj_nstype]`` set to the new namespace. Note that 34through bind mounting and mounts propagation, a task can easily view 35the contents of other namespaces' sysfs mounts. Therefore, when a 36namespace exits, it will call kobj_ns_exit() to invalidate any 37kernfs_node->ns pointers pointing to it. 38 39Users of this interface: 40 41- define a type in the ``kobj_ns_type`` enumeration. 42- call kobj_ns_type_register() with its ``kobj_ns_type_operations`` which has 43 44 - current_ns() which returns current's namespace 45 - netlink_ns() which returns a socket's namespace 46 - initial_ns() which returns the initial namesapce 47 48- call kobj_ns_exit() when an individual tag is no longer valid