Re: [PATCH] cowlinks v2

[Davide Libenzi]

On Sun, 21 Mar 2004, Jörn Engel wrote:

> On Sat, 20 March 2004 08:48:43 -0800, Davide Libenzi wrote:
> > 
> > FWIW I did this quite some time ago to speed up copy+diff linux kernel 
> > trees:
> > 
> > http://www.xmailserver.org/flcow.html
> > 
> > It is entirely userspace and uses LD_PRELOAD on my dev shell.
> 
> Nice work.  I was thinking about something like that as an
> intermediate solution (my goal is libc inclusion), just with slightly
> different checks:
> 
> 	int ret = open(...);
> 	if (ret == -EMLINK)
> 		ret = cow_open(...);
> 	return ret;

When I did that, fumes of an in-kernel implementation invaded my head for 
a little while. Then you start thinking that you have to teach apps of new 
open(2) semantics, you have to bloat kernel code a little bit and you have 
to deal with a new set of errors cases that open(2) is not expected to 
deal with. A fully userspace implementation did fit my needs at that time, 
even if the LD_PRELOAD trick might break if weak aliases setup for open 
functions change inside glibc.



- Davide


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