HermitOS Support

[notgull]

x86_64-unknown-hermit appears to have a poll function similar to Unix. Since we already have a poll-based backend we should be able to integrate it into here.

However from a brief look I can't see whether or not it has an equivalent to pipe or eventfd, which would be needed to implement support here.

[notgull]

@stlankes @mkroening It looks like you are the maintainers of HermitOS. Do you have any insight here?

[stlankes]

I am currently working on it. It will be there in the near future.

[stlankes]

I added a system call poll. Maybe it helps.

[notgull]

I added a system call poll. Maybe it helps.

Thank you! The other thing we need is the ability to wake up the poll from another thread. In Unix, there is an eventfd or pipe, which can be woken up in order to wake up the poll call. In Windows, there is a PostQueuedCompletionStatus function that can be used to wake up a thread waiting on a poll. I'm not sure what's right for HermitOS.

[stlankes]

Yeah, I think that I will add something like eventfd

[notgull]

@stlankes Actually, if we're adding syscalls to Hermit to support this, what would be your opinion on an epoll or kqueue-like API? The poll backend in polling is alright, but just by the nature of poll we can't efficiently poll more than a few thousand sockets depending on the hardware.

It would be preferred to have a kernel API like epoll/kqueue/Solaris event ports that can handle adding/modifying/removing interest in FDs in a scalable fashion.

[stlankes]

I know and we are working on it. But it needs some time.