Add documentation for makedev

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

1 files changed, 54 insertions, 0 deletions

diff --git a/docs/manual/makedev-syntax.txt b/docs/manual/makedev-syntax.txt
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+[[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
+-------------------------------------------------------------------
+