In-kernel file or block I/O is async if the driver/file implemented the async operations. If not, it's blocking. io_uring is a relatively new userspace syscall

In-kernel file or block I/O is async if the driver/file implemented the async operations. If not, it's blocking. io_uring is a relatively new userspace syscall API to minimize the number of syscalls used for I/O, and to provide a common mechanism for doing many kinds of operations. Previously, large numbers of syscalls could become a bottleneck for busy applications, and some kinds of operations did not have a usable non-blocking interface.