Re: [PATCH] cowlinks v2

[Davide Libenzi]

On 21 Mar 2004, Eric W. Biederman wrote:

> Jörn Engel <joern@xxxxxxxxxxxxxxxxxxxx> writes:
> 
> > On Sun, 21 March 2004 09:59:39 -0800, Davide Libenzi wrote:
> > > 
> > > 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.
> > 
> > 209 fairly simple lines definitely have more appear than a full
> > in-kernel implementation with many new corner-cases, yes.  But it
> > looks as if you ignore the -ENOSPC case, so you cheated a little. ;)
> > 
> > No matter how you try, there is no way around an additional return
> > code for open(), so we have to break compatibility anyway.  The good
> > news is that a) people not using this feature won't notice and b) all
> > programs I tried so far can deal with the problem.  Vim even has a
> > decent error message - as if my patch was anticipated already.
> 
> Actually there is...  You don't do the copy until an actual write occurs.
> Some files are opened read/write when there is simply the chance they might
> be written to so delaying the copy is generally a win.

What about open+mmap?
	


- Davide


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