Re: Optional switching off cow in overlayfs

[Jan Olszak <j.olszak@samsung.com>]

On 06/23/2015 06:07 PM, Jan Olszak wrote:
>
> On 06/23/2015 03:23 PM, David Howells wrote:
>> Jan Olszak <j.olszak@samsung.com> wrote:
>>
>>> Why not just say: "rename causes copy" and leave everything as it is 
>>> now.
>> That's another option - but your whole proposal was that we 
>> specifically don't
>> copy up these files IIRC.
>>
>
> Yes, so let's modify the proposal:
>
> Overlayfs checks xattr "trusted.overlay.cow" to switch COW off 
> whenever it's possible.
>
> 1. This would be an optimization/convenience option, not a security 
> option
> 2. By default overlayfs uses COW like it does now
> 3. trusted.overlay.cow=="n" means:
> - Unlink, open, setattr etc. use the original inode from lowerdir
> - Unmodifying operations also use inode from lowerdir
> - Other operations (rename) may copy the file if it's required by the 
> implementation of overlayfs
>
So does it sound upstreamable?

Jan