FreeBSD/Linux Kernel Cross Reference
sys/Documentation/ABI/

	Name	Size	Last modified (GMT)	Description
	Parent directory		2013-02-02 13:13:18
	obsolete/		2013-02-02 13:13:57
	removed/		2013-02-02 13:14:02
	stable/		2013-02-02 13:14:02
	testing/		2013-02-02 13:14:01
	README	3284 bytes	2012-12-25 01:40:34

     This directory attempts to document the ABI between the Linux kernel and
     userspace, and the relative stability of these interfaces.  Due to the
     everchanging nature of Linux, and the differing maturity levels, these
     interfaces should be used by userspace programs in different ways.
     
     We have four different levels of ABI stability, as shown by the four
     different subdirectories in this location.  Interfaces may change levels
     of stability according to the rules described below.
     
    The different levels of stability are:
    
      stable/
            This directory documents the interfaces that the developer has
            defined to be stable.  Userspace programs are free to use these
            interfaces with no restrictions, and backward compatibility for
            them will be guaranteed for at least 2 years.  Most interfaces
            (like syscalls) are expected to never change and always be
            available.
    
      testing/
            This directory documents interfaces that are felt to be stable,
            as the main development of this interface has been completed.
            The interface can be changed to add new features, but the
            current interface will not break by doing this, unless grave
            errors or security problems are found in them.  Userspace
            programs can start to rely on these interfaces, but they must be
            aware of changes that can occur before these interfaces move to
            be marked stable.  Programs that use these interfaces are
            strongly encouraged to add their name to the description of
            these interfaces, so that the kernel developers can easily
            notify them if any changes occur (see the description of the
            layout of the files below for details on how to do this.)
    
      obsolete/
            This directory documents interfaces that are still remaining in
            the kernel, but are marked to be removed at some later point in
            time.  The description of the interface will document the reason
            why it is obsolete and when it can be expected to be removed.
    
      removed/
            This directory contains a list of the old interfaces that have
            been removed from the kernel.
    
    Every file in these directories will contain the following information:
    
    What:           Short description of the interface
    Date:           Date created
    KernelVersion:  Kernel version this feature first showed up in.
    Contact:        Primary contact for this interface (may be a mailing list)
    Description:    Long description of the interface and how to use it.
    Users:          All users of this interface who wish to be notified when
                    it changes.  This is very important for interfaces in
                    the "testing" stage, so that kernel developers can work
                    with userspace developers to ensure that things do not
                    break in ways that are unacceptable.  It is also
                    important to get feedback for these interfaces to make
                    sure they are working in a proper way and do not need to
                    be changed further.
    
    
    How things move between levels:
    
    Interfaces in stable may move to obsolete, as long as the proper
    notification is given.
    
    Interfaces may be removed from obsolete and the kernel as long as the
    documented amount of time has gone by.
    
    Interfaces in the testing state can move to the stable state when the
    developers feel they are finished.  They cannot be removed from the
    kernel tree without going through the obsolete state first.
    
    It's up to the developer to place their interfaces in the category they
    wish for it to start out in.