Need switch to not use eventfd on target_os = "linux"

[haraldh]

For an SGX enclave (using gramine), I can't use the eventfd mechanism. Would be nice, if I could fallback to the pipe mechanism.

Currently I am using haraldh@5852388

But an additional feature might be too much maintenance burden.

Would this help? RUSTFLAGS='--cfg no_eventfd' ... so we can do #[cfg(all(not(no_eventfd), any(target_os = "linux", target_os = "android")))]

[haraldh]

Oh yeah, RUSTFLAGS='--cfg no_eventfd' works great... see master...haraldh:mio:no_eventfd_cfg

[notgull]

Is it a documented issue that eventfd can't be used inside of an SGX enclave, but epoll and pipes can?

[haraldh]

@notgull at least for gramine:
https://gramine.readthedocs.io/en/stable/manifest-syntax.html#allowing-eventfd

[Thomasdezeeuw]

As discussed on Discord, I'm not really a fan of creating a matrix of supported features on top of the matrix of support OSs, it's a burden on maintenance.

However similar things, in the sense of supporting/using a different implementation on an OS that supports a "better" one, has come up before, e.g. #1602. Perhaps we can introduce cfg (not feature) flag for such things, but make it very clear that we don't support it. Then people in very specific situations, like this one, can still use Mio without forking it.