Should `iour` driver panic when not all USER_OPs supported?

[inklesspen1rus]

Found a bit confused situation

fusion driver prefers polling because my machine not support Socket opcode at io_uring.
But when I disable polling feature, iour driver builds successfully.

Should iour driver probe USER_OPs too, like fusion does?
https://github.com/compio-rs/compio/blob/0bc590df25b70911d84cb035a7eb367eb16cd248/compio-driver/src/driver_type.rs#L34C1-L34C26

[Berrysoft]

Oh. Officially we increased the minimum supported kernel version this year, from 5.15 to 5.19, because Ubuntu 20.04 is end of life. The socket op is added in 5.19, so it should be an error on earlier versions... might be a good idea to fallback? But we don't have CI to test it.

[Berrysoft]

Besides socket, bufring and sqe128 are also new features in 5.19.

[inklesspen1rus]

Well... I definetly should check kernel version on my machine 😅
I hoped socket is only thing is preventing me from io-uring, but seems like there are more things.

But I see not probing them a problem, because my app will try execute unsupported opcodes instead of saying "hey, update your linux" and exit.

[Berrysoft]

Socket might be the most common feature here. I think it's possible to add a fallback for it (even specially). The other features might not be that fortunate though.

[Berrysoft]

I opened #507 to make Socket fallback. Does it fix your issue?

[inklesspen1rus]

Yep, all's good, thanks!

[inklesspen1rus]

Wait, no, I forget about probing used opcodes in iour-only case.
That's why I opened 2 issues: 1 for probing and 1 for fallback.

My initial question was about probing opcodes in iour-only builder and return error if some opcodes unsupported.

[inklesspen1rus]

Between, fallback works.

[Berrysoft]

Well, if fallback works, is it necessary to return error if it's unsupported?

I'd like to invite @George-Miao to join the discussion.

[George-Miao]

Maybe we can add an option in ProactorBuilder that enables opcode detection during iouring driver initialization, and return io::ErrorKind::Unsupported if not all opcodes are supported. Even better, maybe we can let user choose what opcodes they want and only run detection on those.