xnvme VS rio

Basically io_uring grew a lot, the latest API offers incredible tools but there are very few examples in any language (xnvme and fio), and in particular I'm struggling to understand how to do it in Rust: where should unsafe code stop? should I simply expose the io_uring api as unsafe, or should I do more work in C and present the ring when ready to rust?

The foundation of xNVMe is libxnvme, a user space library for working with NVMe devices. It provides a C API for memory management, that is, for allocating physical / DMA transferable memory when needed. An NVMe command interface allowing you to submit and complete NVMe commands in a synchronous as well as an asynchronous manner. Similar to libnvme, however, with a focus on I/O performance and portability. Thus, xNVMe and the libxnvme library works not just on Linux, but also on FreeBSD, Windows, and MacOS.

Also, not to be too bad about a reputation fallacy, but I found the author to be flippant and disrespectful when good-faith unsoundness was pointed out in his crates: https://github.com/spacejam/rio/issues/30

In my previous post on linear types I spent quite a bit of time motivating linear types. For example the ergonomic rio io_uring library could be made sound if it could guarantee destructors are run. Or performing FFI with async C++ could be made more efficient if it could rely directly on destructors rather than having to involve an intermediate runtime for each call.

It's like cargo should have a way to mark a dependency as unsafe. That way, you could have a safe mmap crate as an unsafe dependency. Or something like rio which is deliberately unsound (but is fine if you abide by its rules through the entirety of the program)

for completeness there is also rio, but:

rio still has known soundness issues– its Completion futures block the thread when dropped (!!!), and can allow for use-after-free bugs if leaked. See https://github.com/spacejam/rio/issues/30 for details.

Here are some posts about the design. https://without.boats/blog/io-uring/ https://github.com/spacejam/rio/issues/30 https://github.com/axboe/liburing/issues/109

The author of sled[1], an embedded database in Rust which has a number of promising features, has also written parts of rio[2], an underlying pure Rust io_uring library, which is intended to become the core write path for sled. rio has support for files but also has a demo for TCP (on Linux 5.5 and later) and O_DIRECT.

I tested rio recently as I had a Brilliant but Bad Idea™ involving file access and was pleasantly surprised by the API, as I have been with sled's.

I'm excited for the experimentation in the Rust ecosystem and for such low level crates to handle the complex io_uring tasks (relatively) safely!

[1]: https://github.com/spacejam/sled

[2]: https://github.com/spacejam/rio