Comment 78 for bug 2056461

Created attachment 306570
tenative fix to allow reads past cached size for direct IO

Ok so the attached patch (0001-WIP-tenative-fix-to-allow-reads-past-cached-size-for.patch) fixes my reproducer at least, I think it'd "good enough" for testing.

In practice it's probably missing some edge cases and I haven't tested it at all besides my reproducer, so here be dragons.

Next to make it a bit more correct and we're good to go; but I'm surprised this is specific to 9p honestly... Just reading from an already open file in a loop would likely also not notice external appends (on another client) to the file - if it works, how does it work?