Merge tag 'docs-5.3' of git://git.lwn.net/linux

Pull Documentation updates from Jonathan Corbet:
 "It's been a relatively busy cycle for docs:

   - A fair pile of RST conversions, many from Mauro. These create more
     than the usual number of simple but annoying merge conflicts with
     other trees, unfortunately. He has a lot more of these waiting on
     the wings that, I think, will go to you directly later on.

   - A new document on how to use merges and rebases in kernel repos,
     and one on Spectre vulnerabilities.

   - Various improvements to the build system, including automatic
     markup of function() references because some people, for reasons I
     will never understand, were of the opinion that
     :c:func:``function()`` is unattractive and not fun to type.

   - We now recommend using sphinx 1.7, but still support back to 1.4.

   - Lots of smaller improvements, warning fixes, typo fixes, etc"

* tag 'docs-5.3' of git://git.lwn.net/linux: (129 commits)
  docs: automarkup.py: ignore exceptions when seeking for xrefs
  docs: Move binderfs to admin-guide
  Disable Sphinx SmartyPants in HTML output
  doc: RCU callback locks need only _bh, not necessarily _irq
  docs: format kernel-parameters -- as code
  Doc : doc-guide : Fix a typo
  platform: x86: get rid of a non-existent document
  Add the RCU docs to the core-api manual
  Documentation: RCU: Add TOC tree hooks
  Documentation: RCU: Rename txt files to rst
  Documentation: RCU: Convert RCU UP systems to reST
  Documentation: RCU: Convert RCU linked list to reST
  Documentation: RCU: Convert RCU basic concepts to reST
  docs: filesystems: Remove uneeded .rst extension on toctables
  scripts/sphinx-pre-install: fix out-of-tree build
  docs: zh_CN: submitting-drivers.rst: Remove a duplicated Documentation/
  Documentation: PGP: update for newer HW devices
  Documentation: Add section about CPU vulnerabilities for Spectre
  Documentation: platform: Delete x86-laptop-drivers.txt
  docs: Note that :c:func: should no longer be used
  ...

1 files changed, 51 insertions, 0 deletions

diff --git a/Documentation/kbuild/headers_install.rst b/Documentation/kbuild/headers_install.rst
new file mode 100644
index 000000000000..1ab7294e41ac
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+++ b/Documentation/kbuild/headers_install.rst
@@ -0,0 +1,51 @@
+=============================================
+Exporting kernel headers for use by userspace
+=============================================
+
+The "make headers_install" command exports the kernel's header files in a
+form suitable for use by userspace programs.
+
+The linux kernel's exported header files describe the API for user space
+programs attempting to use kernel services.  These kernel header files are
+used by the system's C library (such as glibc or uClibc) to define available
+system calls, as well as constants and structures to be used with these
+system calls.  The C library's header files include the kernel header files
+from the "linux" subdirectory.  The system's libc headers are usually
+installed at the default location /usr/include and the kernel headers in
+subdirectories under that (most notably /usr/include/linux and
+/usr/include/asm).
+
+Kernel headers are backwards compatible, but not forwards compatible.  This
+means that a program built against a C library using older kernel headers
+should run on a newer kernel (although it may not have access to new
+features), but a program built against newer kernel headers may not work on an
+older kernel.
+
+The "make headers_install" command can be run in the top level directory of the
+kernel source code (or using a standard out-of-tree build).  It takes two
+optional arguments::
+
+  make headers_install ARCH=i386 INSTALL_HDR_PATH=/usr
+
+ARCH indicates which architecture to produce headers for, and defaults to the
+current architecture.  The linux/asm directory of the exported kernel headers
+is platform-specific, to see a complete list of supported architectures use
+the command::
+
+  ls -d include/asm-* | sed 's/.*-//'
+
+INSTALL_HDR_PATH indicates where to install the headers. It defaults to
+"./usr".
+
+An 'include' directory is automatically created inside INSTALL_HDR_PATH and
+headers are installed in 'INSTALL_HDR_PATH/include'.
+
+The command "make headers_install_all" exports headers for all architectures
+simultaneously.  (This is mostly of interest to distribution maintainers,
+who create an architecture-independent tarball from the resulting include
+directory.)  You also can use HDR_ARCH_LIST to specify list of architectures.
+Remember to provide the appropriate linux/asm directory via "mv" or "ln -s"
+before building a C library with headers exported this way.
+
+The kernel header export infrastructure is maintained by David Woodhouse
+<dwmw2@infradead.org>.