[touisteur]

I'm looking at the evolution in the chaining capabilities of io_uring. Right now it's a bit basic but I'm guessing in 5 or 6 kernel versions people will have built a micro kernel or a web server just by chaining things in io_uring and maybe some custom chaining/decision blocks in ebpf :-)

[coder543]

BPF, you say? https://lwn.net/Articles/847951/

> The obvious place where BPF can add value is making decisions based on the outcome of previous operations in the ring. Currently, these decisions must be made in user space, which involves potential delays as the relevant process is scheduled and run. Instead, when an operation completes, a BPF program might be able to decide what to do next without ever leaving the kernel. "What to do next" could include submitting more I/O operations, moving on to the next in a series of files to process, or aborting a series of commands if something unexpected happens.

[touisteur]

Yes exactly what I had in mind. I'm also thinking of a particular chain of syscalls [0][1][2][3] (send netlink message, setsockopt, ioctls, getsockopts, reads, then setsockopt, then send netlink message) grouped so as to be done in one sequence without ever surfacing up to userland (just fill those here buffers, who's a good boy!). So now I'm missing ioctls and getsockopts but all in good time!

[0] https://github.com/checkpoint-restore/criu/blob/7686b939d155...

[1] https://github.com/checkpoint-restore/criu/blob/7686b939d155...

[2] https://github.com/checkpoint-restore/criu/blob/7686b939d155...

[3] https://www.infradead.org/~tgr/libnl/doc/api/group__qdisc__p...

[touisteur]

BPF is going to change so many things... At the moment I'm having lots of trouble with the tooling but hey, let's just write BPF bytecode by hand or with a macro-asm. Reduce the ambitions...

[touisteur]

Also wondering whether we should rethink language runtimes for this. Like write everything in SPARK (so all specs are checked), target bpf bytecode through gnatllvm. OK you've written the equivalent of a cuda kernel or tbb::flow block. Now for the chaining y'all have this toolbox of task-chainers (barriers, priority queues, routers...) and you'll never even enter userland? I'm thinking /many/ programs could be described as such.