[PATCH-v4 1/7] vfs: split update_time() into update_time() and write_time()

[Christoph Hellwig]

I don't think this scheme works well.  As mentioned earlier XFS doesn't
even use vfs dirty tracking at the moment, so introducing this in a
hidden way sounds like a bad idea.  Probably the same for btrfs.

I'd rather keep update_time as-is for now, don't add ->write_time and
let btrfs and XFS figure out how to implement the semantics on their
own.