Re: [PATCH] xfs: don't hand out pNFS layouts for reflink inodes

[Christoph Hellwig <hch@xxxxxx>]

On Mon, Mar 28, 2016 at 12:51:40PM -0700, Darrick J. Wong wrote:
> >     /*
> > +    * The pNFS block layout spec actually supports reflink like
> > +    * functionality, but the Linux pNFS server doesn't implement it yet.
> > +    */
> > +   if (!xfs_is_reflink_inode(ip))
> > +           return -ENXIO;
> 
> /me isn't familiar with pNFS, but doesn't this make it so that
> xfs_fs_map_blocks /only/ works on reflinked files?  Maybe I'm misreading the
> comment, but it sounds to me like Linux doesn't support reflinked files over
> pNFS and therefore we want to disable this iomapping functionality any time we
> find a reflinked file.
> 
> But maybe there's a subtlety here that I'm missing?

You jsut missed me fat fingering the check :)

Btw, we'll need something similar to prevent swapfiles which just use
->bmap, but unfortunately swap just checks for the existences of method,
so I'll probably have to do some VFS changes to properly support that.