linux-kernel - Re: Copy on write hard links?

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Date:	Wed, 25 Sep 2013 16:28:53 +0200
From:	Thomas Meyer <thomas@...3r.de>
To:	Rob Landley <rob@...dley.net>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Copy on write hard links?

Am Mittwoch, den 25.09.2013, 08:59 -0500 schrieb Rob Landley:
> On 09/24/2013 01:36:56 PM, Thomas Meyer wrote:
> > Hi,
> > 
> > Is there such a thing?
> 
> In the kernel's vfs layer? 

Yes, that would be a nice feature!

> No, although some filesystems (ala btrfs) do  
> things like that with snapshots.
> 
> In userspace? Breaking hardlinks when updating a file is fairly normal,  
> that's why they distinguish between "truncate and rewrite" (preserve  
> hardlinks) and "write new file and rename over old file" (break  
> hardlinks, avoiding the more obvious race conditions).

so every user space application needs to implement that for itself?
I wonder how hard it would be to implement this on vfs layer? linkat()
with a new flag as api or something like that.

> 
> Rob

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