linux-kernel - Re: [PATCH v5 5/5] block: loop: support DIO & AIO

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Date:	Tue, 23 Jun 2015 10:59:36 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Dave Kleikamp <dave.kleikamp@...cle.com>,
	Jens Axboe <axboe@...nel.dk>, Zach Brown <zab@...bo.net>,
	Maxim Patlasov <mpatlasov@...allels.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Tejun Heo <tj@...nel.org>, Dave Chinner <david@...morbit.com>
Subject: Re: [PATCH v5 5/5] block: loop: support DIO & AIO

On Tue, Jun 23, 2015 at 12:00 AM, Christoph Hellwig <hch@...radead.org> wrote:
> On Mon, Jun 22, 2015 at 08:09:55PM +0800, Ming Lei wrote:
>> For the general async interface, it is a bit complicated than sync interfaces:
>>
>> -  iocb need to be one parameter, because it often depends on callers, such
>> as loop can preallocate it
>> - direct I/O need to be another parameter(in loop we can use the same helper
>> to handle sync request)
>> - bvec and the segment number are another two parameters
>> - not mention the common parameters(file, offset, pos, complete...)
>
> We only really need iocb + iov_iter, they carry everything we need.

Then the helper becomes the fowllowing:

ssize_t vfs_iter_async_write(struct kiocb *kiocb, struct iov_iter *iter)
{
       ssize_t ret;

       iter->type |= WRITE;
       ret = file->f_op->write_iter(&kiocb, iter);

       return ret;
}

I am wondering its value and we can do that easily in call site, also it isn't
easy to name it since sometimes we may need to let the helper handle
sync requests, such as loop's case.

Thanks,
Ming
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