Re: [PATCH v2 1/4] aio: add aio_kernel_() interface

[Ming Lei <ming.lei@canonical.com>]

On Tue, Jan 27, 2015 at 1:00 AM, Christoph Hellwig <hch@infradead.org> wrote:
> On Tue, Jan 27, 2015 at 12:18:23AM +0800, Ming Lei wrote:
>> > Also it might make sense to just offer aio_kernel_read/write intefaces
>> > instead of the common submit wrapper, as that's much closer to other
>> > kernel APIs, e.g.
>> >
>> > int aio_kernel_read(struct kiocb *iocb, struct file *file,
>> >                 struct iov_iter *iter, loff_t off,
>> >                 void (*complete)(struct kiocb *iocb, long res));
>> > int aio_kernel_write(struct kiocb *iocb, struct file *file,
>> >                 struct iov_iter *iter, loff_t off,
>> >                 void (*complete)(struct kiocb *iocb, long res));
>>
>> It is like style of sync APIs, looks submit/complete is common
>> for async APIs, like io_submit().
>
> io_submit is a fairly horrible API.  While Posix AIO isn't too much
> better it does have separate APIs for read/write.  Given that there
> isn't much code shared I'd keep an API that feels familar.

But from performance view, the two APIs of aio_kernel_read()
and aio_kernel_write() aren't good because both need
5 parameters which can't be held in registers and they are
often called from single thread context, not like synchronized
read() and write().

Also aio_kernel_init_rw() can be moved to header file as inline
to avoid too many parameters.

Thanks,
Ming Lei