Function io_uring_register 

pub unsafe fn io_uring_register(
    fd: &impl AsRawFd,
    opcode: u32,
    args: &[*const u8],
) -> Result<()>

Registers a resource on the io_uring instance so that it can be used in submition entries.

Safety

args must contain valid data. What this means depends on the opcode. io_uring documentation or implementation.