linux-kernel - Re: Feature request: exec self for NOMMU.

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Message-Id: <200612261939.57359.rob@landley.net>
Date:	Tue, 26 Dec 2006 19:39:56 -0500
From:	Rob Landley <rob@...dley.net>
To:	David Lang <david.lang@...italinsight.com>
Cc:	linux-kernel@...r.kernel.org,
	David McCullough <david_mccullough@...securecomputing.com>
Subject: Re: Feature request: exec self for NOMMU.

On Tuesday 26 December 2006 6:55 pm, David Lang wrote:
> > Worse, it's not always possible.  If chroot() has happened since the 
program
> > 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?  
Hmmm...

> 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...)

Rob
-- 
"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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