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

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Date:	Sun, 29 Sep 2013 18:19:05 +0100
From:	Pádraig Brady <P@...igBrady.com>
To:	Richard Weinberger <richard.weinberger@...il.com>
CC:	Thomas Meyer <thomas@...3r.de>, Rob Landley <rob@...dley.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Copy on write hard links?

On 09/29/2013 08:14 AM, Richard Weinberger wrote:
> On Sun, Sep 29, 2013 at 7:22 AM, Pádraig Brady <P@...igbrady.com> wrote:
>> On 09/25/2013 03:37 PM, richard -rw- weinberger wrote:
>>> On Wed, Sep 25, 2013 at 4:28 PM, Thomas Meyer <thomas@...3r.de> wrote:
>>>> 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!
>>>
>>> You mean reflinks?
>>> Currently only OCFS2 and btrfs support them.
>>> Both using a fs specific ioctl().
>>> IIRC GNU cp uses the btrfs specific one if the --reflink parameter is used.
>>
>> coreutils is waiting for a reflink syscall to materialize
>> rather than adding new per filesystem support
>> http://lwn.net/Articles/335380/
> 
> Is this the correct link? It's a proposal for a reflink() syscall.
> But corrently both OCFS2 and btrfs are using ioctl().
> 
> Digging into GNU coreutils shows that their cp's
> clone_file() only supports the btrfs ioctl().
> I don't know what the GNU folks big plan is, maybe you know more. :-)

The current coreutils plan is to not to call any more file system specific ioctls,
rather waiting until a more general syscall is available.

thanks,
Pádraig.
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