[PATCH] Add kernel<->userspace ABI stability documentation

Signed-off-by: Kay Sievers <kay.sievers@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

6 files changed, 171 insertions, 0 deletions

diff --git a/Documentation/ABI/README b/Documentation/ABI/README
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index 000000000000..9feaf16f1617
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+++ b/Documentation/ABI/README
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+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.
+        The file Documentation/feature-removal-schedule.txt may describe
+        some of these interfaces, giving a schedule for when they will
+        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.
diff --git a/Documentation/ABI/obsolete/devfs b/Documentation/ABI/obsolete/devfs
new file mode 100644
index 000000000000..b8b87399bc8f
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+++ b/Documentation/ABI/obsolete/devfs
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+What:           devfs
+Date:           July 2005
+Contact:        Greg Kroah-Hartman <gregkh@suse.de>
+Description:
+        devfs has been unmaintained for a number of years, has unfixable
+        races, contains a naming policy within the kernel that is
+        against the LSB, and can be replaced by using udev.
+        The files fs/devfs/*, include/linux/devfs_fs*.h will be removed,
+        along with the the assorted devfs function calls throughout the
+        kernel tree.
+
+Users:
+
diff --git a/Documentation/ABI/stable/syscalls b/Documentation/ABI/stable/syscalls
new file mode 100644
index 000000000000..c3ae3e7d6a0c
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+++ b/Documentation/ABI/stable/syscalls
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+What:           The kernel syscall interface
+Description:
+        This interface matches much of the POSIX interface and is based
+        on it and other Unix based interfaces.  It will only be added to
+        over time, and not have things removed from it.
+
+        Note that this interface is different for every architecture
+        that Linux supports.  Please see the architecture-specific
+        documentation for details on the syscall numbers that are to be
+        mapped to each syscall.
diff --git a/Documentation/ABI/stable/sysfs-module b/Documentation/ABI/stable/sysfs-module
new file mode 100644
index 000000000000..75be43118335
--- /dev/null
+++ b/Documentation/ABI/stable/sysfs-module
@@ -0,0 +1,30 @@
+What:           /sys/module
+Description:
+        The /sys/module tree consists of the following structure:
+
+        /sys/module/MODULENAME
+                The name of the module that is in the kernel.  This
+                module name will show up either if the module is built
+                directly into the kernel, or if it is loaded as a
+                dyanmic module.
+
+        /sys/module/MODULENAME/parameters
+                This directory contains individual files that are each
+                individual parameters of the module that are able to be
+                changed at runtime.  See the individual module
+                documentation as to the contents of these parameters and
+                what they accomplish.
+
+                Note: The individual parameter names and values are not
+                considered stable, only the fact that they will be
+                placed in this location within sysfs.  See the
+                individual driver documentation for details as to the
+                stability of the different parameters.
+
+        /sys/module/MODULENAME/refcnt
+                If the module is able to be unloaded from the kernel, this file
+                will contain the current reference count of the module.
+
+                Note: If the module is built into the kernel, or if the
+                CONFIG_MODULE_UNLOAD kernel configuration value is not enabled,
+                this file will not be present.
diff --git a/Documentation/ABI/testing/sysfs-class b/Documentation/ABI/testing/sysfs-class
new file mode 100644
index 000000000000..4b0cb891e46e
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+++ b/Documentation/ABI/testing/sysfs-class
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+What:           /sys/class/
+Date:           Febuary 2006
+Contact:        Greg Kroah-Hartman <gregkh@suse.de>
+Description:
+                The /sys/class directory will consist of a group of
+                subdirectories describing individual classes of devices
+                in the kernel.  The individual directories will consist
+                of either subdirectories, or symlinks to other
+                directories.
+
+                All programs that use this directory tree must be able
+                to handle both subdirectories or symlinks in order to
+                work properly.
+
+Users:
+        udev <linux-hotplug-devel@lists.sourceforge.net>
diff --git a/Documentation/ABI/testing/sysfs-devices b/Documentation/ABI/testing/sysfs-devices
new file mode 100644
index 000000000000..6a25671ee5f6
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+++ b/Documentation/ABI/testing/sysfs-devices
@@ -0,0 +1,25 @@
+What:           /sys/devices
+Date:           February 2006
+Contact:        Greg Kroah-Hartman <gregkh@suse.de>
+Description:
+                The /sys/devices tree contains a snapshot of the
+                internal state of the kernel device tree.  Devices will
+                be added and removed dynamically as the machine runs,
+                and between different kernel versions, the layout of the
+                devices within this tree will change.
+
+                Please do not rely on the format of this tree because of
+                this.  If a program wishes to find different things in
+                the tree, please use the /sys/class structure and rely
+                on the symlinks there to point to the proper location
+                within the /sys/devices tree of the individual devices.
+                Or rely on the uevent messages to notify programs of
+                devices being added and removed from this tree to find
+                the location of those devices.
+
+                Note that sometimes not all devices along the directory
+                chain will have emitted uevent messages, so userspace
+                programs must be able to handle such occurrences.
+
+Users:
+        udev <linux-hotplug-devel@lists.sourceforge.net>