Arguably asyc/await could help with this; obviously it didn't exist in 1991 when Linux was created but it would be interesting to revisit this topic.

Wouldn't that just consist of I/O operations returning futures and then having an await() block the calling thread until the future is done (i.e. put it on a waitqueue)?

With Rust in the kernel this becomes somewhat possible to conceptualize.

You’d probably want to use either some sort of code generation to do the requisite CPS transform[1] or the Duff’s-device-like preprocessor trick[2], but it’s definitely doable with some compiler support. Not in an existing codebase, though.

(Brought to you by working on a C codebase that does express stuff like this as explicit callbacks and context structures. Ugh.)

[1] https://dx.doi.org/10.1007/s10990-012-9084-5, https://www.irif.fr/~jch/research/cpc-2012.pdf, https://github.com/kerneis/cpc

[2] https://www.chiark.greenend.org.uk/~sgtatham/coroutines.html