sort out the fallocate mode mess v2

Christoph Hellwig
2024-08-27T06:51:31Z

Hi all,

I've recently been looking at the XFS fallocate implementation and got
upset about the messing parsing of the mode argument, which mixes modes
and an optional flag in a really confusing way.

This series tries to clean this up by better defining what is the
operation mode and what is an optional flag, so that both the core
code and file systems can use switch statements to switch on the mode.

Changes since v1:
- fix the IS_APPEND check
- ensure space is allocated after unshare