Re: Feature request: exec self for NOMMU.

From: Rob Landley
Date: Tue Dec 26 2006 - 19:45:46 EST

On Tuesday 26 December 2006 6:55 pm, David Lang wrote:
> > Worse, it's not always possible. If chroot() has happened since the
> > started, there may not _be_ a path to my current executable available from
> > this process's current or root directories.
> does this even make sense (as a general purpose function)? if the executable
> isn't available in your path it's likly that any config files it needs are
> not available either.

For a statically linked busybox it makes sense, but you're right that a
dynamically linked one is going to suck however you do it...

I guess what I really want to do is promote a vfork() to a real fork() after
the fact. Which sounds painful.

For the daemonize() case I want to unblock the parent and have it exit. Too
bad I can't call clone() with some kind of CLONE_VFORK_BACKWARDS so it blocks
the child until the parent exits. (Hmmm... CLONE_STOPPED doesn't help, just
moves the race...)

For the "new process runs code out of this executable" case what I really want
is an actual fork, hideously expensive as that is on nommu systems. (There
are things I can do to minimize that.) Maybe I can call clone() directly on
a nommu system to get it to fork, even when the C library hasn't got it?

> for something like busybox/toolbox where you have different functions based
> on the name used to execute the program, which name would you use?

The one from argv[0]. (Notice how exec has a "path to executable" and then an
argv array? Nobody said that the path to executable and argv[0] had to point
to the same string...)

"Perfection is reached, not when there is no longer anything to add, but
when there is no longer anything to take away." - Antoine de Saint-Exupery
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