Getting Started with QNX Neutrino - QNX Software Systems

© 2009, QNX Software Systems GmbH & Co. KG. Advanced topics
d_offset
d_reclen
d_namelen
d_name
The offset into the directory we just talked about above. In our
example, this will be a simple number like “0,” “1,” “2,” etc.
The size of the entire struct dirent field and any extensions that
may be placed within it. The size includes any alignment filler
required.
The number of characters in the d_name field, not including the NUL
terminator.
The name of this directory entry, which must be NUL terminated.
When returning the struct dirent entries, the return code passed back to the client
is the number of bytes returned.
Example
In this example, we’re going to create a resource manager called /dev/atoz that will
be a directory resource manager. It’s going to manifest the “files” /dev/atoz/a
through to dev/atoz/z, with a cat of any of the files returning the uppercase letter
corresponding to the filename. Here’s a sample command-line session to give you an
idea of how this works:
# cd /dev
# ls
atoz null ptyp2 socket ttyp0 ttyp3
enet0 ptyp0 ptyp3 text ttyp1 zero
mem ptyp1 shmem tty ttyp2
# ls -ld atoz
dr-xr-xr-x 1 root 0 26 Sep 05 07:59 atoz
# cd atoz
# ls
a e i m q u y
b f j n r v z
c g k o s w
d h l p t x
# ls -l e
-r--r--r-- 1 root 0 1 Sep 05 07:59 e
# cat m
M# cat q
Q#
The example above illustrates that the directory atoz shows up in the /dev directory,
and that you can do an ls of the directory itself and cd into it. The /dev/atoz
directory has a size of “26,” which is the number that we selected in the code. Once in
the atoz directory, doing another ls shows the contents — the files a through z.
Doing an ls of a particular file, say e, shows that the file is readable by all (the
-r--r--r-- part) and is one byte in size. Finally, doing a few random cat’s shows
that the files indeed have the stated contents. (Note that since the files contain only one
byte, there’s no linefeed after the character is printed, which is why the prompt shows
up on the same line as the output.)
Now that we’ve seen the characteristics, let’s take a look at the code, which is
organized into the following functions:
April 30, 2009 Chapter 5 • Resource Managers 275