Process Working Directory

[kubeos]

Well, I finally got around to fixing my old multitasking code. Everything SEEMS to be working fine now.

But I'm wondering what others have done about a process's current working directory. If I launch a program in the background and it is working with files, then I change to a different directory in my shell, things can really get messed up. What I was thinking of doing is, when a program is launched, it records the current drive and directory into it's process structure. Every time the program needs to save or load a file, the kernel will change to the program's directory. If the program changes directory, then that will replace what was originally recorded.

Is this similar to what anyone else has done?

[NickJohnson]

That is usually how it works - the working directory is stored in each process structure, and changing one won't change the others.

[kubeos]

Okay, I just started coding it up. Works like a charm so far. lcc is compiling and linking a test program perfectly while I'm in a different directory.

[Troy Martin]

Another solution: don't implement directory support

I'm already regretting that route and I'm writing a simple LFN/directory layer to fix that

[skyking]

Another solution may be to implement the current directory in user space. That is letting the C library have a global variable that is used to convert filenames to absolute filenames before accessing the file. That's what I've planned to use and I don't see any big problems with that. Do you?

[Combuster]

If you have considered how to pass the initial PWD to the application, then I don't see any problems.

[Velko]

I'm planning to implement working directory in userspace as well. But, instead of using plain global variable I'm going to use PWD environment variable.

There's one "small" problem trough - I haven't figured out a decent way to pass environment variables to new process yet

How do you, guys, handle those?

[Troy Martin]

Well, my kernel is... unusual...

As of TBOS 1.1.0 (in development hell ) the internal shell's command line is passed in SI and the current drive number is passed in DL.

[skyking]

I'm planning to implement working directory in userspace as well. But, instead of using plain global variable I'm going to use PWD environment variable.

There's one "small" problem trough - I haven't figured out a decent way to pass environment variables to new process yet

How do you, guys, handle those?

Well simply add a few parameters to create_process that then is used as parameter to the process entry point. For example you could set a pointer and data length and fill the memory block with whatever you would like (environment, command line parameters etc).

[Kevin]

In tyndur, the initialization code of the new process asks its parent for the environment variables via normal IPC functions. The current working directory is one of them.

[skyking]

In tyndur, the initialization code of the new process asks its parent for the environment variables via normal IPC functions. The current working directory is one of them.

This might result in a race condition if the parent changes the working directory (or even terminates) between the start of the child and the IPC-message.

[Kevin]

True. You can have hacks in place that "work for now", but you should never forget they are hacks, like I did here.

[Combuster]

Even so, if you are aware of the possibility, you can design it in.