kernel space getcwd()? (using current() to find out cwd)

From: Michael L. Welles (mike@bangstate.com)
Date: Mon Apr 16 2001 - 17:42:52 EST

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This is probably a stupid question, and probably directed to the wrong
list. Apologies in advance, but I'm stumped

I've been working on a kernel module to report on "changed files". It
works just fine -- I wrap the orignal system calls with my
replacements which queue the filenames being modified, and when
another proccess reads from the device or proc entry, they get a nice
snapshot of what's going on in the system -- except that all the paths
are relative to the calling process.

So, a little ignorance being a dangerous thing, I thought I'd be clever
and manually reconstruct the full path by walking up
current->fs->pwd->d_parent and padding d_name to the filename until it
hits root.

Unfortunatly, this approach causes kernel panics. e.g., the attached
code snippet will inevitably bring down the machine if I call it
during in my replacement open, mkdir, rmdir, unlink routines -- and
tehy all work fine without itq.

What am I not getting? I do see, before I go down, that there's a few
occasions where current() is NULL...

Apologies in advance for a wordy, probably stupid question, but I'm
stumped.

If this is not the right approach for what I'm trying to do (e.g. a
kernel space getcwd()), can someone point me to something else I can try?

Thanks in advance,

Mike Welles

----------------------------------------

(this is the greatly reduced version which does nothing but try and
reference current->fs->pwd)

void fill_full_path(char *name)
{
    if (current==NULL)
    {
#ifdef DEBUG
          printk("ERROR! current == NULL\n");
#endif
          return;
    }

  if (current->fs==NULL)
    {
#ifdef DEBUG
          printk("ERROR! current-> == NULL\n");
#endif
          return;
    }

  if (current->fs->pwd==NULL)
    {
#ifdef DEBUG
          printk("ERROR! current->fs->pwd == NULL\n");
#endif
          return;
    }

return;
}

This is probably a stupid question: I've been working on a kernel
module to report on "changed files".

It works just fine -- I wrap the orignal system calls with my
replacements which queue the filenames being modified, and when
another proccess reads from the device or proc entry, they get a nice
snapshot of what's going on in the system -- except that all the paths
are relative to the calling process.