Add more comments to libc-fs-with-isolation test

[tiif]

Add comments to explain why we test syscalls that need disable isolation mode in isolation mode.

[tiif]

@rustbot ready

[RalfJung]

Looking at this again when I am more awake ;)

These tests do not "require disable-isolation". These tests test what happens when you have isolation enabled, and set -Zmiri-isolation-error=warn-nobacktrace. It's important to test that. So we definitely do not want to move these tests anywhere else -- we want to test the behavior of all our APIs both with and without isolation.

[RalfJung]

@rustbot author

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[tiif]

These tests do not "require disable-isolation". These tests test what happens when you have isolation enabled, and set -Zmiri-isolation-error=warn-nobacktrace. It's important to test that. So we definitely do not want to move these tests anywhere else -- we want to test the behavior of all our APIs both with and without isolation.

Ahh this makes sense, thanks for explaining! I will move the test back and add this to comment later.

[tiif]

Alright, I just add more comment there

@rustbot ready

[RalfJung]

This looks great, thanks! After resolving the last nit, please squash the commits using ./miri squash. Then write @rustbot ready after you pushed the squashed PR.

@rustbot author

[tiif]

@rustbot ready