Re: [PATCH v6 4/5] fs, xfs: introduce MAP_DIRECT for creating block-map-atomic file ranges

[Christoph Hellwig]

I still can't make any sense of this description.  What is an external
agent?  Userspace obviously can't ever see a change in the extent
map, so it can't be meant.

It would help a lot if you could come up with a concrete user for this,
including example code.