Update Rust to use new system calls

[thaliaarchi]

Since the last release of hermit-abi, version 0.4.0, a few system calls have been added, including mmap and seek. If a new version of hermit-abi were published to crates.io, then rust-lang/rust could take advantage of those features.

Relevant new features:

• 6978f30 (add support of the system calls mmap/munmap, 2024-06-24)
• 87dd201 (add missing interface for lseek, 2024-07-15) (reported in Support std::fs::File::seek #652)
• Maybe 9b05f27 (add example to use the vsock interface, 2023-08-07)

(If Rust isn't using every feature introduced before 0.4.0, then there may be more.)

I'd be happy to fix the missing seek on the rust-lang/rust side. (Also, if tell was added to Hermit, then I could add support in Rust in rust-lang/rust#137165 (Use tell for <File as Seek>::stream_position).)

[mkroening]

Thanks for bringing these up! :)

I'll coordinate a new hermit-abi release, but maybe lseek should go into the libc crate directly if we are confident about the interface.

mmap is not finalized right now, since it is not POSIX conformant right now. We have to discuss whether we want to stick with the current design or change the system call to be POSIX compatible.

I am not sure how vsock is relevant for std, but confirming the stability and publishing would be a good thing anyway. Then we can expose them via vsock-rs.

There might actually more things missing from std that are present in the kernel. I have been looking into that a bit, but did not do a thorough check yet.

[thaliaarchi]

maybe lseek should go into the libc crate directly if we are confident about the interface.

I didn't know the libc crate supported Hermit. The soon-to-be-current version of stdio for Hermit is merged with Unix stdio, but uses symbols from hermit_abi instead of libc. It sounds like it would be good to move those and others that are stable over to libc.

[mkroening]

Yeah, that's the plan in the long run. I think that PR should not be blocked on using things from hermit-abi, though. It's fine to use the upstream definitions from hermit-abi. That's how we used to do it until recently, when we started moving things that we have high confidence in into libc with the long time goal to move to libc for as much as possible.

[thaliaarchi]

@mkroening Hey, friendly ping! Just a reminder about this, in case you were intending to make a hermit-abi release but had forgotten.

[mkroening]

Thanks for the ping! hermit-abi version 0.5.0 is now published. :)

[thaliaarchi]

I've opened rust-lang/rust#138074 to add support for lseek to std. Since that's the only part of this issue which immediately impacts rust-lang/rust, we could close this. When I last looked, I didn't see any abstraction for mmap in std, so that's probably not relevant. Likewise for the vsock-rs part.

However, if this issue is still useful for you as a sort of tracking issue, we could also keep it open or repurpose it.

[mkroening]

I have opened a separate issue regarding vsock (#671). We can open another one for mmap once it becomes relevant, and we have properly reworked the kernel API.

Thank you so much for opening this issue in the first place! :)