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- Add a SPDX header; - Adjust document title; - Some whitespace fixes and new line breaks; - Mark literal blocks as such; - Add it to filesystems/index.rst. Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org> Link: https://lore.kernel.org/r/45a01fa5edd5c6ee8fc0754fc74f7ef65a3e5581.1588021877.git.mchehab+huawei@kernel.org Signed-off-by: Jonathan Corbet <corbet@lwn.net>
49 lines
1.9 KiB
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49 lines
1.9 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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=============
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Sysfs tagging
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=============
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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 a namespace via the
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``void *ns member`` of its ``kernfs_node``. If a directory entry is tagged,
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then ``kernfs_node->flags`` will have a flag between KOBJ_NS_TYPE_NONE
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and KOBJ_NS_TYPES, and ns will point to the namespace to which it
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belongs.
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Each sysfs superblock's kernfs_super_info contains an array
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``void *ns[KOBJ_NS_TYPES]``. When 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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kernfs_node->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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