Re: Create subvolume from a directory?

[Hubert Kario <hka@qbs.com.pl>]

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On Wednesday 02 of May 2012 18:33:37 David Sterba wrote:
> On Tue, May 01, 2012 at 07:09:21PM +0200, Hubert Kario wrote:
> > Let me rephrase it:
> > 
> > People don't want to be able to do:
> > 
> > mount /dev/lvm/btrfs /mnt/a -t btrfs -o subvol=volA
> > mount /dev/lvm/btrfs /mnt/b -t btrfs -o subvol=volB
> > cp --reflink=always /mnt/a/file /mnt/b
> > 
> > Just like you can't do hardlinks over `mount --bind` mountpoints, you
> > shouldn't be able to cp reflink over mountpoints. That's expected as this
> > *does* break VFS semantics.
> 
> Proposed fix (incremental on top of the cross-subvol):

I'm a noob as far as kernel development is concerned so take my comments for 
what they're worth.
 
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -2321,6 +2321,10 @@ static noinline long btrfs_ioctl_clone(struct file
> *file, unsigned long srcfd, goto out_drop_write;
>         }
> 
> +       ret = -EXDEV;
> +       if (src_file->f_path.mnt != file->f_path.mnt)

I'm not sure about this comparision. Is the f_path struct member used just as 
reference to some general kernel structure?

> +               goto out_fput;
> +
>         src = src_file->f_dentry->d_inode;
> 
>         ret = -EINVAL;

Other that that, looks OK.

Regards,
-- 
Hubert Kario
QBS - Quality Business Software
02-656 Warszawa, ul. Ksawerów 30/85
tel. +48 (22) 646-61-51, 646-74-24
www.qbs.com.pl

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