From: Jan Olszak <j.olszak@samsung.com>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: David Howells <dhowells@redhat.com>,
"linux-unionfs@vger.kernel.org" <linux-unionfs@vger.kernel.org>
Subject: Re: Optional switching off cow in overlayfs
Date: Mon, 22 Jun 2015 15:45:18 +0200 [thread overview]
Message-ID: <5588116E.20509@samsung.com> (raw)
In-Reply-To: <CAJfpegsP-_MAKybYZ=uS3UCxsxL9Hv-cJ-GYrVL4h3B+tWZF9A@mail.gmail.com>
On 06/22/2015 01:32 PM, Miklos Szeredi wrote:
> 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
> --
> To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in
>
The lower fs is most likely ext4.
Unfortunately making a file immutable won't solve the problem. There's
nothing wrong in modifying the file and it should stay possible.
I just want to switch off copy on write for some files. Can you see
another way?
If you are OK with the optional xattr, then I'll prepare the patch.
Thanks,
Jan
next prev parent reply other threads:[~2015-06-22 13:45 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-18 13:25 Optional switching off cow in overlayfs Jan Olszak
2015-06-18 13:39 ` David Howells
2015-06-18 14:43 ` Jan Olszak
2015-06-22 11:32 ` Miklos Szeredi
2015-06-22 13:45 ` Jan Olszak [this message]
2015-06-22 13:53 ` Miklos Szeredi
2015-06-22 14:26 ` Jan Olszak
2015-06-22 14:37 ` Miklos Szeredi
2015-06-22 15:32 ` Jan Olszak
2015-06-23 9:27 ` David Howells
2015-06-23 10:36 ` Jan Olszak
2015-06-23 13:23 ` David Howells
2015-06-23 16:05 ` Jan Olszak
2015-06-23 16:07 ` Jan Olszak
2015-06-24 16:03 ` Jan Olszak
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