Subject: bug#6048: bug#11443: linux "cp" and ocfs2 reflink/clone/fastcopy/copy on write

From: Assaf Gordon <[email-masked]>
Date: Wed, 10 Oct 2018 10:53:55 -0600

(triaging old bugs)

On 14/05/12 07:19 AM, Pádraig Brady wrote:
> On 05/09/2012 03:28 PM, Kai Petzke wrote:

>> there has been work by others about adding support for the OCFS2
>> "reflink" ioctl() call, which is similiar to the btrfs "clone"
>> call, and creates a copy-on-write copy of the original, thus
>> allowing to "copy" even gigabyte sized files within a tiny fraction
>> of a second, and without using much additional file system space.
>> See:
[...]

>> even though the interface to use to different system calls to achieve the same thing is awkward.
>> But, as laid out in the comments in the source, btrfs clone and ocfs2 reflink are semantically
>> quite different, so that unifying them into one on the kernel side is not likely to happen, soon, if it happens at all.
> 
> That would be unfortunate. Hopefully a generic reflink() call can be sorted out.

In 2014 we had this commit:
https://git.savannah.gnu.org/cgit/coreutils.git/commit/?id=b47231be6813e6cb5305266e391b4bb745f27f13
====
commit b47231be6813e6cb5305266e391b4bb745f27f13
Author: David Sterba <[email-masked]>
Date:   Wed Sep 24 11:15:05 2014 +0100

     mv: use reflink=auto mode by default

     On some filesystems (BTRFS), moving a file within the filesystem may
     cross subvolume boundaries and we can use a lightweight reflink copy,
     similar to what cp(1) can do, which is faster than a full file copy.
====

Does this 'reflink=auto' mode addresses OCFS2 as well?
I believe so, but want to double-check.

If there are no objections, I'll mark this as "fixed/done" in couple of 
days.

regards,
  - assaf