Add documentation for makedev

* +LIBFOO_DEVICES+ lists the device files to be created by Buildroot

  when using the static device table. The syntax to use is the

  makedevs one.

  makedevs one. You can find some documentation for this syntax in the

  xref:makedev-syntax[]. This variable is optional.

* +LIBFOO_PERMISSIONS+ lists the changes of permissions to be done at

  the end of the build process. The syntax is once again the makedevs one.

  You can find some documentation for this syntax in the xref:makedev-syntax[].

  This variable is optional.

The recommended way to define these variables is to use the following

syntax:

Appendix

========

include::makedev-syntax.txt[]

[[makedev-syntax]]

Makedev syntax documentation

----------------------------

The makedev syntax is used across several places in Buildroot to

define changes to be made for permissions or which device files to

create and how to create them, in order to avoid to call mkdnod every

now and then.

This syntax is derived from the makedev utility, and a more complete

documentation can be found in the +package/makedevs/README+ file.

It takes the form of a line for each file, with the following layout:

|===========================================================

|name |type |mode |uid |gid |major |minor |start |inc |count

|===========================================================

There is a few non-trivial blocks here:

- +name+ is the path to the file you want to create/modify

- +type+ is the type of the file, being one of :

  * f: a regular file

  * d: a directory

  * c: a character device file

  * b: a block device file

  * p: a named pipe

- +mode+, +uid+ and +gid+ are the usual permissions stuff

- +major+ and +minor+ are here for device files

- +start+, +inc+ and +count+ are when you want to create a whole batch

  of files, and can be reduced to a loop, beginning at +start+,

  incrementing its counter by +inc+ until it reaches +count+

Let's say you want to change the permissions of a given file, using

this syntax, you will need to put:

-------------------------------------------------------------------

/usr/bin/foobar	f	644	0	0	-	-	-	-	-

-------------------------------------------------------------------

On the other hand, if you want to create the device file +/dev/hda+

and the corresponding 15 files for the partitions, you will need for

+/dev/hda+:

-------------------------------------------------------------------

/dev/hda	b	640	0	0	3	0	0	0	-

-------------------------------------------------------------------

and then for device files corresponding to the partitions of

+/dev/hda+, +/dev/hdaX+, +X+ ranging from 1 to 15:

-------------------------------------------------------------------

/dev/hda	b	640	0	0	3	1	1	1	15

-------------------------------------------------------------------

include::download-location.txt[]

include::adding-packages.txt[]

include::appendix.txt[]