Btrfs devel - Jan 2010 - Re: cp --reflink with Btrfs

* Sage Weil (sage@newdream.net) [091216 17:55]:
> On Wed, 16 Dec 2009, Li Dongyang wrote:
> 
> > Have a look at line 998, ioctl.c, inside btrfs_ioctl_clone(),
> > the src->i_size(the size of the testfile created by touch) is just
0, and this
> > will cause btrfs_ioctl_clone just return -EINVAL.
> > I''m not sure if it makes sense to clone a file which actually
doesn''t have any
> > data extents.
> 
> Probably not, but it seems more consistent to return success instead than 
> -EINVAL.  Requiring the caller to check and special case empty files
isn''t
> very friendly...

Actually it makes lots of sense if trying to e.g. cow-copy an chroot
on an buildd, and there are some empty files inside of the linux
installation (which normally just are).

Can I hope on getting the patch (or another patch) incorporated into
the kernel?



Cheers,
Andi
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On Wed, Jan 27, 2010 at 11:53:22AM +0100, Andreas Barth
wrote:
> * Sage Weil (sage@newdream.net) [091216 17:55]:
> > On Wed, 16 Dec 2009, Li Dongyang wrote:
> > 
> > > Have a look at line 998, ioctl.c, inside btrfs_ioctl_clone(),
> > > the src->i_size(the size of the testfile created by touch) is
just 0, and this
> > > will cause btrfs_ioctl_clone just return -EINVAL.
> > > I''m not sure if it makes sense to clone a file which
actually doesn''t have any
> > > data extents.
> > 
> > Probably not, but it seems more consistent to return success instead
than
> > -EINVAL.  Requiring the caller to check and special case empty files
isn''t
> > very friendly...
> 
> 
> Actually it makes lots of sense if trying to e.g. cow-copy an chroot
> on an buildd, and there are some empty files inside of the linux
> installation (which normally just are).
> 
> Can I hope on getting the patch (or another patch) incorporated into
> the kernel?
In this case the application is responsible for duplicating the file.
The clone ioctl doesn''t actually clone any of the file metadata or
anything else.

-chris

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