Re: BTRFS file clone support for cp

[Pádraig Brady]

Giuseppe Scrivano wrote:
> Jim Meyering <address@hidden> writes:
> 
>> I am now convinced that cp's new behavior belongs on
>> a separate option, --reflink (i.e., it should not be the default).
>> Giuseppe, do you feel like adding that option and adjusting your
>> test accordingly?
> 
> I attached two separate patches, --reflink option and file-clone test.
> Last versions of btrfs have a bug (I asked on #btrfs and they confirmed
> it), btrfs doesn't use correctly all the free space available.  In fact
> I get ENOSPC while in reality only 54% is used.  Probably it is better
> to postpone the second patch inclusion after the bug is fixed.

That explains some of the weirdness I noticed.
Thanks for looking into it.
(there was also weird values for `du cloned_file`)

> Another note, I changed this line in the NEWS file:
> -  "when both the source and destination are on the same btrfs partition."
> 
> considering that BTRFS supports multiple devices I am not convinced that
> it is always true, I guess source and destination could be on different
> partitions, though I couldn't find a clear answer on the btrfs wiki to
> this question.

I would very much doubt one could clone outside a single file system.
If a file system can span multiple devices/partitions then maybe.
In any case would be better to say "file system" rather than "partition",
as the latter is not directly related.

cheers,
Pádraig.