[RFC PATCH 02/17] vfs: Implement a FIEMAP callback

[Christoph Hellwig]

On Wed, Mar 04, 2026 at 02:03:09PM +0000, David Howells wrote:
> Implement a callback in the internal kernel FIEMAP API so that kernel users
> can make use of it as the filler function expects to write to userspace.
> This allows the FIEMAP data to be captured and parsed.  This is useful for
> cachefiles and also potentially for knfsd and ksmbd to implement their
> equivalents of FIEMAP remotely rather than using SEEK_DATA/SEEK_HOLE.

Hell no.  FIEMAP is purely a debugging toool and must not get anywhere
near a data path.  NAK to all of this.