revisiting "Hard link across subvolumes"

revisiting "Hard link across subvolumes"

[David Nicol]

could i-node numbers be made unique on a whole device, or somehow
adjusted to avoid collisions, instead of simply disallowing this
useful operation?

On Thu, Oct 7, 2010 at 4:13 PM, Goffredo Baroncelli <kreijack@libero.it=
> wrote:

> The link across subvolumes is not allowable. =C2=A0In the beginning i=
t was
> possible, but that was source of bugs. See the thread "Hard link acro=
ss
> subvolumes"
>
> http://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg03286.html
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Re: revisiting "Hard link across subvolumes"

[Goffredo Baroncelli]

On Saturday, 09 October, 2010, you (David Nicol) wrote:
> could i-node numbers be made unique on a whole device, or somehow
> adjusted to avoid collisions, instead of simply disallowing this
> useful operation?

In case of a snapshot make sense to preserve the inode number.

> On Thu, Oct 7, 2010 at 4:13 PM, Goffredo Baroncelli <kreijack@libero.it> 
wrote:
> 
> > The link across subvolumes is not allowable.  In the beginning it was
> > possible, but that was source of bugs. See the thread "Hard link across
> > subvolumes"
> >
> > http://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg03286.html
> 


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Re: revisiting "Hard link across subvolumes"

[David Nicol]

when i have some time to work on this I will figure out a way to pull
inodes from a larger pool or include the subvolume id at creation time
in them or something so that the collisions go away. Surely it must be
possible to prefix or suffix the inode number with a few bits that are
per-subvolume unique.

On Sat, Oct 9, 2010 at 8:44 AM, Goffredo Baroncelli <kreijack@libero.it=
> wrote:
>
> In case of a snapshot make sense to preserve the inode number.



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Re: revisiting "Hard link across subvolumes"

[Tomasz Chmielewski]

>> The link across subvolumes is not allowable.  In the beginning it was
>> possible, but that was source of bugs. See the thread "Hard link across
>> subvolumes"
>>
>> http://www.mail-archive.com/linux-btrfs <at> vger.kernel.org/msg03286.html

Similar for cp --reflink across subvolumes - also won't work.

If btrfs is to support deduplication one day, it has to work across 
subvolumes - otherwise, it won't be very useful.


-- 
Tomasz Chmielewski
http://wpkg.org