forked from Minki/linux
b9d8b45ee3
The first three paragraphs are almost verbatim taken from Eric's commit message on the patch introducing network ns tags. The next two paragraphs I wrote to be a brief high level overview. The last section is taken from the commit message on "Implement sysfs tagged directory support", but updated. Hopefully correctly. Signed-off-by: Serge E. Hallyn <serue@us.ibm.com> Cc: Eric W. Biederman <ebiederm@xmission.com> Cc: Tejun Heo <tj@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
43 lines
1.8 KiB
Plaintext
43 lines
1.8 KiB
Plaintext
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
|