Re: io uring support for character device

[Jens Axboe <axboe@kernel.dk>]

On 5/24/22 6:56 PM, Changman Lee wrote:
> Hi List,
> 
> I'm CM Lee. I'm developing a custom character device managing pcie dma.
> I've tried to use io uring for the char device which supports readv
> and writev with synchronous and blocking manner and seek.
> When I use a io uring with IORING_SETUP_IOPOLL and IORING_SETUP_SQPOLL
> for reducing syscall overhead, a readv of the char device driver seems
> to be not called. So I added a_ops->direct_IO when the device is
> opened with O_DIRECT. But the result was the same.
> This is my question.
> Q1: Does io uring support a character device ?
> Q2: Is it better to reimplement a device driver as block device type ?

io_uring doesn't care what file type it is, I suspect your problem lies
elsewhere. Do you have a ->read() defined as well? If you do, the vfs
will pick that over ->read_iter().

If regular read/write works with O_DIRECT and reading from the device in
general, then io_uring will too.

-- 
Jens Axboe