Driver implementer's guide for kernel side

[twhitlock]

Dear all,

Apologies if this isn't the place to ask questions about the kernel-mode side of io_uring, but I don't know where else to ask such a question.

Is there a detailed guide somewhere on how io_uring interacts with a driver, i.e. a Linux kernel module? I've seen a couple of example drivers that implement read_iter & write_iter file_operations, but they're trivial and don't address a lot of real-world issues like cancelation, clean up, indefinite waits etc. Reading the kernel source code has helped a little, but to be honest I don't understand well enough the kernel VFS layer or the io_uring kernel implementation to draw firm conclusions.

Background: I've been implementing a PCIe endpoint driver intended for the High Performance Computing market (we want millions of zero-copy DMA IOPS if possible). During the course of that, I've come up with a few questions and concerns that I haven't been able to answer by reading kernel source code or looking at drivers that implement async. I/O.

If there is no such guide, then I don't mind starting something, e.g. a Wiki.