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>
42 lines
1.8 KiB
Text
42 lines
1.8 KiB
Text
Sysfs tagging
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(Taken almost verbatim from Eric Biederman's netns tagging patch
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commit msg)
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The problem. Network devices show up in sysfs and with the network
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namespace active multiple devices with the same name can show up in
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the same directory, ouch!
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To avoid that problem and allow existing applications in network
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namespaces to see the same interface that is currently presented in
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sysfs, sysfs now has tagging directory support.
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By using the network namespace pointers as tags to separate out the
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the sysfs directory entries we ensure that we don't have conflicts
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in the directories and applications only see a limited set of
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the network devices.
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Each sysfs directory entry may be tagged with zero or one
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namespaces. A sysfs_dirent is augmented with a void *s_ns. If a
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directory entry is tagged, then sysfs_dirent->s_flags will have a
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flag between KOBJ_NS_TYPE_NONE and KOBJ_NS_TYPES, and s_ns will
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point to the namespace to which it belongs.
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Each sysfs superblock's sysfs_super_info contains an array void
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*ns[KOBJ_NS_TYPES]. When a a task in a tagging namespace
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kobj_nstype first mounts sysfs, a new superblock is created. It
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will be differentiated from other sysfs mounts by having its
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s_fs_info->ns[kobj_nstype] set to the new namespace. Note that
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through bind mounting and mounts propagation, a task can easily view
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the contents of other namespaces' sysfs mounts. Therefore, when a
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namespace exits, it will call kobj_ns_exit() to invalidate any
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sysfs_dirent->s_ns pointers pointing to it.
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Users of this interface:
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- define a type in the kobj_ns_type enumeration.
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- call kobj_ns_type_register() with its kobj_ns_type_operations which has
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- current_ns() which returns current's namespace
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- netlink_ns() which returns a socket's namespace
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- initial_ns() which returns the initial namesapce
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- call kobj_ns_exit() when an individual tag is no longer valid
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