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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 a namespace via the
- void *ns member of its kernfs_node. If a directory entry is tagged,
- then kernfs_node->flags will have a flag between KOBJ_NS_TYPE_NONE
- and KOBJ_NS_TYPES, and ns will point to the namespace to which it
- belongs.
- Each sysfs superblock's kernfs_super_info contains an array void
- *ns[KOBJ_NS_TYPES]. When 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
- kernfs_node->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- - call kobj_ns_exit() when an individual tag is no longer valid
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