docs: early-userspace: move to driver-api guide

Those documents describe a kAPI. So, add to the driver-api
book.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

3 files changed, 0 insertions, 291 deletions

diff --git a/Documentation/early-userspace/buffer-format.rst b/Documentation/early-userspace/buffer-format.rst
deleted file mode 100644
index 7f74e301fdf3..000000000000
--- a/Documentation/early-userspace/buffer-format.rst
+++ /dev/null
@@ -1,119 +0,0 @@
-=======================
-initramfs buffer format
-=======================
-
-Al Viro, H. Peter Anvin
-
-Last revision: 2002-01-13
-
-Starting with kernel 2.5.x, the old "initial ramdisk" protocol is
-getting {replaced/complemented} with the new "initial ramfs"
-(initramfs) protocol.  The initramfs contents is passed using the same
-memory buffer protocol used by the initrd protocol, but the contents
-is different.  The initramfs buffer contains an archive which is
-expanded into a ramfs filesystem; this document details the format of
-the initramfs buffer format.
-
-The initramfs buffer format is based around the "newc" or "crc" CPIO
-formats, and can be created with the cpio(1) utility.  The cpio
-archive can be compressed using gzip(1).  One valid version of an
-initramfs buffer is thus a single .cpio.gz file.
-
-The full format of the initramfs buffer is defined by the following
-grammar, where::
-
-	*	is used to indicate "0 or more occurrences of"
-	(|)	indicates alternatives
-	+	indicates concatenation
-	GZIP()	indicates the gzip(1) of the operand
-	ALGN(n)	means padding with null bytes to an n-byte boundary
-
-	initramfs  := ("\0" | cpio_archive | cpio_gzip_archive)*
-
-	cpio_gzip_archive := GZIP(cpio_archive)
-
-	cpio_archive := cpio_file* + (<nothing> | cpio_trailer)
-
-	cpio_file := ALGN(4) + cpio_header + filename + "\0" + ALGN(4) + data
-
-	cpio_trailer := ALGN(4) + cpio_header + "TRAILER!!!\0" + ALGN(4)
-
-
-In human terms, the initramfs buffer contains a collection of
-compressed and/or uncompressed cpio archives (in the "newc" or "crc"
-formats); arbitrary amounts zero bytes (for padding) can be added
-between members.
-
-The cpio "TRAILER!!!" entry (cpio end-of-archive) is optional, but is
-not ignored; see "handling of hard links" below.
-
-The structure of the cpio_header is as follows (all fields contain
-hexadecimal ASCII numbers fully padded with '0' on the left to the
-full width of the field, for example, the integer 4780 is represented
-by the ASCII string "000012ac"):
-
-============= ================== ==============================================
-Field name    Field size	 Meaning
-============= ================== ==============================================
-c_magic	      6 bytes		 The string "070701" or "070702"
-c_ino	      8 bytes		 File inode number
-c_mode	      8 bytes		 File mode and permissions
-c_uid	      8 bytes		 File uid
-c_gid	      8 bytes		 File gid
-c_nlink	      8 bytes		 Number of links
-c_mtime	      8 bytes		 Modification time
-c_filesize    8 bytes		 Size of data field
-c_maj	      8 bytes		 Major part of file device number
-c_min	      8 bytes		 Minor part of file device number
-c_rmaj	      8 bytes		 Major part of device node reference
-c_rmin	      8 bytes		 Minor part of device node reference
-c_namesize    8 bytes		 Length of filename, including final \0
-c_chksum      8 bytes		 Checksum of data field if c_magic is 070702;
-				 otherwise zero
-============= ================== ==============================================
-
-The c_mode field matches the contents of st_mode returned by stat(2)
-on Linux, and encodes the file type and file permissions.
-
-The c_filesize should be zero for any file which is not a regular file
-or symlink.
-
-The c_chksum field contains a simple 32-bit unsigned sum of all the
-bytes in the data field.  cpio(1) refers to this as "crc", which is
-clearly incorrect (a cyclic redundancy check is a different and
-significantly stronger integrity check), however, this is the
-algorithm used.
-
-If the filename is "TRAILER!!!" this is actually an end-of-archive
-marker; the c_filesize for an end-of-archive marker must be zero.
-
-
-Handling of hard links
-======================
-
-When a nondirectory with c_nlink > 1 is seen, the (c_maj,c_min,c_ino)
-tuple is looked up in a tuple buffer.  If not found, it is entered in
-the tuple buffer and the entry is created as usual; if found, a hard
-link rather than a second copy of the file is created.  It is not
-necessary (but permitted) to include a second copy of the file
-contents; if the file contents is not included, the c_filesize field
-should be set to zero to indicate no data section follows.  If data is
-present, the previous instance of the file is overwritten; this allows
-the data-carrying instance of a file to occur anywhere in the sequence
-(GNU cpio is reported to attach the data to the last instance of a
-file only.)
-
-c_filesize must not be zero for a symlink.
-
-When a "TRAILER!!!" end-of-archive marker is seen, the tuple buffer is
-reset.  This permits archives which are generated independently to be
-concatenated.
-
-To combine file data from different sources (without having to
-regenerate the (c_maj,c_min,c_ino) fields), therefore, either one of
-the following techniques can be used:
-
-a) Separate the different file data sources with a "TRAILER!!!"
-   end-of-archive marker, or
-
-b) Make sure c_nlink == 1 for all nondirectory entries.
diff --git a/Documentation/early-userspace/early_userspace_support.rst b/Documentation/early-userspace/early_userspace_support.rst
deleted file mode 100644
index 3deefb34046b..000000000000
--- a/Documentation/early-userspace/early_userspace_support.rst
+++ /dev/null
@@ -1,154 +0,0 @@
-=======================
-Early userspace support
-=======================
-
-Last update: 2004-12-20 tlh
-
-
-"Early userspace" is a set of libraries and programs that provide
-various pieces of functionality that are important enough to be
-available while a Linux kernel is coming up, but that don't need to be
-run inside the kernel itself.
-
-It consists of several major infrastructure components:
-
-- gen_init_cpio, a program that builds a cpio-format archive
-  containing a root filesystem image.  This archive is compressed, and
-  the compressed image is linked into the kernel image.
-- initramfs, a chunk of code that unpacks the compressed cpio image
-  midway through the kernel boot process.
-- klibc, a userspace C library, currently packaged separately, that is
-  optimized for correctness and small size.
-
-The cpio file format used by initramfs is the "newc" (aka "cpio -H newc")
-format, and is documented in the file "buffer-format.txt".  There are
-two ways to add an early userspace image: specify an existing cpio
-archive to be used as the image or have the kernel build process build
-the image from specifications.
-
-CPIO ARCHIVE method
--------------------
-
-You can create a cpio archive that contains the early userspace image.
-Your cpio archive should be specified in CONFIG_INITRAMFS_SOURCE and it
-will be used directly.  Only a single cpio file may be specified in
-CONFIG_INITRAMFS_SOURCE and directory and file names are not allowed in
-combination with a cpio archive.
-
-IMAGE BUILDING method
----------------------
-
-The kernel build process can also build an early userspace image from
-source parts rather than supplying a cpio archive.  This method provides
-a way to create images with root-owned files even though the image was
-built by an unprivileged user.
-
-The image is specified as one or more sources in
-CONFIG_INITRAMFS_SOURCE.  Sources can be either directories or files -
-cpio archives are *not* allowed when building from sources.
-
-A source directory will have it and all of its contents packaged.  The
-specified directory name will be mapped to '/'.  When packaging a
-directory, limited user and group ID translation can be performed.
-INITRAMFS_ROOT_UID can be set to a user ID that needs to be mapped to
-user root (0).  INITRAMFS_ROOT_GID can be set to a group ID that needs
-to be mapped to group root (0).
-
-A source file must be directives in the format required by the
-usr/gen_init_cpio utility (run 'usr/gen_init_cpio -h' to get the
-file format).  The directives in the file will be passed directly to
-usr/gen_init_cpio.
-
-When a combination of directories and files are specified then the
-initramfs image will be an aggregate of all of them.  In this way a user
-can create a 'root-image' directory and install all files into it.
-Because device-special files cannot be created by a unprivileged user,
-special files can be listed in a 'root-files' file.  Both 'root-image'
-and 'root-files' can be listed in CONFIG_INITRAMFS_SOURCE and a complete
-early userspace image can be built by an unprivileged user.
-
-As a technical note, when directories and files are specified, the
-entire CONFIG_INITRAMFS_SOURCE is passed to
-usr/gen_initramfs_list.sh.  This means that CONFIG_INITRAMFS_SOURCE
-can really be interpreted as any legal argument to
-gen_initramfs_list.sh.  If a directory is specified as an argument then
-the contents are scanned, uid/gid translation is performed, and
-usr/gen_init_cpio file directives are output.  If a directory is
-specified as an argument to usr/gen_initramfs_list.sh then the
-contents of the file are simply copied to the output.  All of the output
-directives from directory scanning and file contents copying are
-processed by usr/gen_init_cpio.
-
-See also 'usr/gen_initramfs_list.sh -h'.
-
-Where's this all leading?
-=========================
-
-The klibc distribution contains some of the necessary software to make
-early userspace useful.  The klibc distribution is currently
-maintained separately from the kernel.
-
-You can obtain somewhat infrequent snapshots of klibc from
-https://www.kernel.org/pub/linux/libs/klibc/
-
-For active users, you are better off using the klibc git
-repository, at http://git.kernel.org/?p=libs/klibc/klibc.git
-
-The standalone klibc distribution currently provides three components,
-in addition to the klibc library:
-
-- ipconfig, a program that configures network interfaces.  It can
-  configure them statically, or use DHCP to obtain information
-  dynamically (aka "IP autoconfiguration").
-- nfsmount, a program that can mount an NFS filesystem.
-- kinit, the "glue" that uses ipconfig and nfsmount to replace the old
-  support for IP autoconfig, mount a filesystem over NFS, and continue
-  system boot using that filesystem as root.
-
-kinit is built as a single statically linked binary to save space.
-
-Eventually, several more chunks of kernel functionality will hopefully
-move to early userspace:
-
-- Almost all of init/do_mounts* (the beginning of this is already in
-  place)
-- ACPI table parsing
-- Insert unwieldy subsystem that doesn't really need to be in kernel
-  space here
-
-If kinit doesn't meet your current needs and you've got bytes to burn,
-the klibc distribution includes a small Bourne-compatible shell (ash)
-and a number of other utilities, so you can replace kinit and build
-custom initramfs images that meet your needs exactly.
-
-For questions and help, you can sign up for the early userspace
-mailing list at http://www.zytor.com/mailman/listinfo/klibc
-
-How does it work?
-=================
-
-The kernel has currently 3 ways to mount the root filesystem:
-
-a) all required device and filesystem drivers compiled into the kernel, no
-   initrd.  init/main.c:init() will call prepare_namespace() to mount the
-   final root filesystem, based on the root= option and optional init= to run
-   some other init binary than listed at the end of init/main.c:init().
-
-b) some device and filesystem drivers built as modules and stored in an
-   initrd.  The initrd must contain a binary '/linuxrc' which is supposed to
-   load these driver modules.  It is also possible to mount the final root
-   filesystem via linuxrc and use the pivot_root syscall.  The initrd is
-   mounted and executed via prepare_namespace().
-
-c) using initramfs.  The call to prepare_namespace() must be skipped.
-   This means that a binary must do all the work.  Said binary can be stored
-   into initramfs either via modifying usr/gen_init_cpio.c or via the new
-   initrd format, an cpio archive.  It must be called "/init".  This binary
-   is responsible to do all the things prepare_namespace() would do.
-
-   To maintain backwards compatibility, the /init binary will only run if it
-   comes via an initramfs cpio archive.  If this is not the case,
-   init/main.c:init() will run prepare_namespace() to mount the final root
-   and exec one of the predefined init binaries.
-
-Bryan O'Sullivan <bos@serpentine.com>
diff --git a/Documentation/early-userspace/index.rst b/Documentation/early-userspace/index.rst
deleted file mode 100644
index 2b8eb6132058..000000000000
--- a/Documentation/early-userspace/index.rst
+++ /dev/null
@@ -1,18 +0,0 @@
-:orphan:
-
-===============
-Early Userspace
-===============
-
-.. toctree::
-    :maxdepth: 1
-
-    early_userspace_support
-    buffer-format
-
-.. only::  subproject and html
-
-   Indices
-   =======
-
-   * :ref:`genindex`