docs/manual: extend makedev syntax section

The section of the manual describing the makedev syntax is not
up-to-date with the current features, and does not properly describe
existing ones.

  - extend the list of types with the requirements on the existence of
    the target file or directory; for 'c', 'b', and 'p', the existence
    requirement is inherited from mknod(2):

    ERRORS
        ...
        ENOENT A directory component in pathname does not exist or is a
               dangling symbolic link.

    for the other types, the existence requirements are extracted from
    the source of makedev.c;

  - format the types flags, so they are rendered in monospace;

  - extend the 'mode' description, as it can be set to -1 for 'f', 'd',
    or 'r', so that only the uid and gid are set. This is most useful
    for 'r', where setting the same mode recursively for all the
    sub-directories and files alike does not really make sense; indeed
    in this case, the modes are usually set correctly when the package
    (or rootfs overlay) installs the files, and only the uid and gid are
    interesting to set;

  - extend and update the examples to show-case the -1 mode use-case.

Signed-off-by: Yann E. MORIN <yann.morin@orange.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

docs/manual/makedev-syntax.adoc

@@ -22,14 +22,19 @@ There are a few non-trivial blocks:
 
 - +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
+  * `f`: a regular file, which must already exist
-  * d: a directory
+  * `F`: a regular file, which is ignored and not created if missing
-  * r: a directory recursively
+  * `d`: a directory, which is created, as well as its parents, if missing
-  * c: a character device file
+  * `r`: a directory recursively, which must already exist
-  * b: a block device file
+  * `c`: a character device file, which parent directory must exist
-  * p: a named pipe
+  * `b`: a block device file, which parent directory must exist
+  * `p`: a named pipe, which parent directory must exist
 - +mode+ are the usual permissions settings (only numerical values
-  are allowed)
+  are allowed);
+  for type `d`, the mode of existing parents is not changed, but the mode
+  of created parents is set;
+  for types `f`, `F`, and `r`, +mode+ can also be set to +-1+ to not
+  change the mode (and only change uid and gid)
 - +uid+ and +gid+ are the UID and GID to set on this file; can be
   either numerical values or actual names
 - +major+ and +minor+ are here for device files, set to +-+ for other
@@ -38,22 +43,22 @@ There are a few non-trivial blocks:
   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
+Let's say you want to change the ownership and permissions of a given
-this syntax, you will need to write:
+file; using this syntax, you will need to write:
 
 ----
 /usr/bin/foo f 755 0 0 - - - - -
 /usr/bin/bar f 755 root root - - - - -
 /data/buz f 644 buz-user buz-group - - - - -
+/data/baz f -1 baz-user baz-group - - - - -
 ----
 
-Alternatively, if you want to change owner/permission of a directory
+Alternatively, if you want to change owner of a directory recursively,
-recursively, you can write (to set UID to foo, GID to bar and access
+you can write (to set UID to `foo` and GID to `bar` for the directory
-rights to rwxr-x--- for the directory /usr/share/myapp and all files
+`/usr/share/myapp` and all files and directories below it):
-and directories below it):
 
 ----
-/usr/share/myapp r 750 foo bar - - - - -
+/usr/share/myapp r -1 foo bar - - - - -
 ----
 
 On the other hand, if you want to create the device file +/dev/hda+