This PR adds a runtime validation mode to check adherence to alignment
and size-multiple requirements at the VirtualFile level.
This can help prevent alignment bugs from slipping into production
because test systems may have more lax requirements than production.
(This is not the case today, but it could change in the future).
It also allows catching O_DIRECT bugs on systems that don't have
O_DIRECT (macOS).
Consequently, we can now accept
`virtual_file_io_mode={direct,direct-rw}` on macOS now.
This has the side benefit of removing some annoying conditional
compilation around `IoMode`.
A third benefit is that it helped weed out size-multiple requirement
violation bugs in how the VirtualFile unit tests exercise read and write
APIs.
I seized the opportunity to trim these tests down to what actually
matters, i.e., exercising of the `OpenFiles` file descriptor cache.
Lastly, this PR flips the binary-built-in default to `DirectRw` so that
when running Python regress tests and benchmarks without specifying
`PAGESERVER_VIRTUAL_FILE_IO_MODE`, one gets the production behavior.
Refs
- fixes https://github.com/neondatabase/neon/issues/11676
## Problem
We had retained the ability to run in a generation-less mode to support
test_generations_upgrade, which was replaced with a cleaner backward
compat test in https://github.com/neondatabase/neon/pull/10701
## Summary of changes
- Remove all the special cases for "if no generation" or "if no control
plane api"
- Make control_plane_api config mandatory
---------
Co-authored-by: Arpad Müller <arpad-m@users.noreply.github.com>
