I'm not sure about the details for file I/O; files with FMODE_NOWAIT should be fine (block devices, ext4, btrfs, ...). The idea is that during submission an op

I'm not sure about the details for file I/O; files with FMODE_NOWAIT should be fine (block devices, ext4, btrfs, ...). The idea is that during submission an operation is started with IOCB_NOWAIT; an operation shouldn't block with that. If it returns EAGAIN it will be retried in another kernel thread without IOCB_NOWAIT. Afaik IOCB_NOWAIT support should be announced through FMODE_NOWAIT. Right now operations that don't support IOCB_NOWAIT ("magic check" in io_file_supports_async [1]) are still run during submission but without the IOCB_NOWAIT flag. Sockets/pipes don't handle IOCB_NOWAIT, they only care about O_NONBLOCK right now (which is a bug imho). [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/io_uring.c?h=v5.1#n823 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin...