Write my own 'everything is a file' interface

Question

I would like to expose the settings and statistics of my program in a 'everything is a file' manner - sort of how /proc/ and /sys/ works.

As an example, imagine for a moment that apache2 had this type of interface. You would then be able to do something like this (hypothetical):

cd /apache2/virtual_hosts
mkdir 172.20.30.50
cd 172.20.30.50
echo '/www/example1' > DocumentRoot
echo 'www.example1.com' > ServerName
echo 1 > control/enabled
cat control/status
   enabled true
   uptime 4080
   hits 0

Now, are there any tutorials or similar on how to do this? I'm mainly looking for techniques for 'pretending to be a file or dir'. I'm on linux, POSIX or other more portable method would be preferable, but not required.

Answer 1

On Linux, have a look at Fuse: implement a fully functional filesystem in a userspace program.

• Simple library API
• Simple installation (no need to patch or recompile the kernel)
• Secure implementation
• Userspace - kernel interface is very efficient
• Usable by non privileged users
• Runs on Linux kernels 2.4.X and 2.6.X
• Has proven very stable over time

Look at compatible platforms here. In terms of tutorial, one of good ones I've came across is here.

Answer 2

In addition to FUSE, another solution is to export a 9p filesystem. wmii does this, for example.

Answer 3

Perhaps the way to do this is just use "real" files and use a change-notification library (inotify preferred) to detect when they change and update your behaviour accordingly.

The /proc and /sys are for kernel-user communication and not really intended for userspace programs' IPC - you're expected to use named pipes, sockets, shared memory etc for that.

(ab)using FUSE is not really a nice idea in this case, I think.