From mboxrd@z Thu Jan  1 00:00:00 1970
From: Miklos Szeredi <miklos@szeredi.hu>
Subject: Re: Optional switching off cow in overlayfs
Date: Mon, 22 Jun 2015 13:32:09 +0200
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To: Jan Olszak <j.olszak@samsung.com>
Cc: David Howells <dhowells@redhat.com>, "linux-unionfs@vger.kernel.org" <linux-unionfs@vger.kernel.org>

On Thu, Jun 18, 2015 at 4:43 PM, Jan Olszak <j.olszak@samsung.com> wrote:
>
>
> On 06/18/2015 03:39 PM, David Howells wrote:
>>
>> Jan Olszak <j.olszak@samsung.com> wrote:
>>
>>> I was wondering about a small improvement to overlayfs - optional, per
>>> file
>>> copy of write.
>>>
>>> 1. By default overlayfs would work as usual.
>>> 2. If a file in 'lower' filesystem has an xattr set
>>> (e.g. trusted.overlay.cow=n) the file would not be copied.
>>>
>>> What do you think?
>>
>> Ummm.  What's the use case?  How do you handle the file being part of
>> multiple
>> overlays?
>>
>> David
>>
>
> I wan't to achieve 'files' granularity in overlayfs instead of 'directory'
> granularity.
> It would be useful in Linux containers configuration. Sometimes you don't
> have the
> power to change the images that are run inside containers and in one folder
> you have both:
> - files that have to be copied
> - files that don't really need to be copied
>
>
> trusted.overlay.cow==n indicates switching off copying the file to the upper
> layer.
> So with multiple overlays you would always have only one file from the
> lower-most dir.

What type filesystem is the lowest layer?   Can you set immutable on
it (chattr +i)?  That would be the logical way to say "nobody can
modify this file, not even root".

Thanks,
Miklos