| 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| - call kobj_ns_exit() when an individual tag is no longer valid |
