Re: [PATCH, RFC] xfs: re-enable FIBMAP on reflink; disable for swap

[Christoph Hellwig <hch@lst.de>]

On Thu, Aug 30, 2018 at 11:28:49AM -0700, Darrick J. Wong wrote:
> I prefer to have FIBMAP return errors to *cough* encourage people to use
> FIEMAP.  If code are going to abuse the FI[BE]MAP interface they could
> at least abuse the one that gives it enough context to avoid fs
> corruption.  (A proper fs driver would be preferable, though very
> difficult).

I think Carlos was looking into implementing the FIBMAP ioctl
using ->fiemap.  In that case we could return sensible errors,
and centralize policy in a single place..

> Granted, grub's blocklist code doesn't seem to check for shared blocks
> when it writes grubenv.... yuck, though TBH I don't have the eye budget
> to spend on digging through grub2.  Frankly I think FIBMAP comes verrry
> close to "this API is unfixably stupid and shouldn't be enabled for new
> use cases and should go away some day".

.. and that policy should be: always return an error for the slightest
unusual file layout (shared, encrypted, inline, etc).