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Discussion at Kernel Summit made it clear that the presence or absence of specific Kconfig symbols are not considered ABI, and that no userspace (or bootloader, etc) should rely on them. In addition, kernel-internal symbols are well established as non-ABI, per Documentation/stable_api_nonsense.txt. Document both of these in Documentation/ABI/README, in a new section for notable bits of non-ABI. Signed-off-by: Josh Triplett <josh@joshtriplett.org> Cc: Rob Landley <rob@landley.net> Cc: Tao Ma <boyu.mt@taobao.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Acked-by: H. Peter Anvin <hpa@zytor.com> Cc: Richard Weinberger <richard.weinberger@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
88 lines
3.7 KiB
Plaintext
88 lines
3.7 KiB
Plaintext
This directory attempts to document the ABI between the Linux kernel and
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userspace, and the relative stability of these interfaces. Due to the
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everchanging nature of Linux, and the differing maturity levels, these
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interfaces should be used by userspace programs in different ways.
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We have four different levels of ABI stability, as shown by the four
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different subdirectories in this location. Interfaces may change levels
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of stability according to the rules described below.
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The different levels of stability are:
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stable/
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This directory documents the interfaces that the developer has
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defined to be stable. Userspace programs are free to use these
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interfaces with no restrictions, and backward compatibility for
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them will be guaranteed for at least 2 years. Most interfaces
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(like syscalls) are expected to never change and always be
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available.
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testing/
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This directory documents interfaces that are felt to be stable,
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as the main development of this interface has been completed.
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The interface can be changed to add new features, but the
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current interface will not break by doing this, unless grave
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errors or security problems are found in them. Userspace
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programs can start to rely on these interfaces, but they must be
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aware of changes that can occur before these interfaces move to
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be marked stable. Programs that use these interfaces are
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strongly encouraged to add their name to the description of
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these interfaces, so that the kernel developers can easily
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notify them if any changes occur (see the description of the
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layout of the files below for details on how to do this.)
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obsolete/
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This directory documents interfaces that are still remaining in
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the kernel, but are marked to be removed at some later point in
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time. The description of the interface will document the reason
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why it is obsolete and when it can be expected to be removed.
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removed/
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This directory contains a list of the old interfaces that have
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been removed from the kernel.
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Every file in these directories will contain the following information:
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What: Short description of the interface
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Date: Date created
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KernelVersion: Kernel version this feature first showed up in.
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Contact: Primary contact for this interface (may be a mailing list)
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Description: Long description of the interface and how to use it.
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Users: All users of this interface who wish to be notified when
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it changes. This is very important for interfaces in
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the "testing" stage, so that kernel developers can work
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with userspace developers to ensure that things do not
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break in ways that are unacceptable. It is also
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important to get feedback for these interfaces to make
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sure they are working in a proper way and do not need to
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be changed further.
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How things move between levels:
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Interfaces in stable may move to obsolete, as long as the proper
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notification is given.
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Interfaces may be removed from obsolete and the kernel as long as the
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documented amount of time has gone by.
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Interfaces in the testing state can move to the stable state when the
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developers feel they are finished. They cannot be removed from the
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kernel tree without going through the obsolete state first.
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It's up to the developer to place their interfaces in the category they
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wish for it to start out in.
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Notable bits of non-ABI, which should not under any circumstances be considered
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stable:
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- Kconfig. Userspace should not rely on the presence or absence of any
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particular Kconfig symbol, in /proc/config.gz, in the copy of .config
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commonly installed to /boot, or in any invocation of the kernel build
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process.
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- Kernel-internal symbols. Do not rely on the presence, absence, location, or
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type of any kernel symbol, either in System.map files or the kernel binary
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itself. See Documentation/stable_api_nonsense.txt.
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