clone ioctl return values

[Christoph Hellwig]

On Mon, Nov 16, 2015 at 04:28:22PM -0800, Darrick J. Wong wrote:
> > -XFS_IOC_CLONE_RANGE: Invalid argument
> > +reflink: Invalid argument
> >  Try reflink past EOF
> > -XFS_IOC_CLONE_RANGE: Invalid argument
> > +reflink: Invalid argument
> >  Try to reflink a dir
> > -XFS_IOC_CLONE_RANGE: Is a directory
> > +reflink: Is a directory
> 
> >  Try to reflink a device
> > -XFS_IOC_CLONE_RANGE: Invalid argument
> > +/mnt/test/test-157/dev1: No such device or address
> 
> Huh.  How did you get -ENODEV here?  I ran this on 4.3 and got -EINVAL.

Turns out this is because my system doesn't have the ramdisk driver
built into the kernel, so opening your block device with major 8, minor
0 already fails.  Might be better to create a char device with
major 1, minor 3 (dev null) as that should always be present.