linux-kernel - Re: splice methods in character device driver

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Date:	Mon, 8 Jun 2009 09:05:04 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Leon Woestenberg <leon.woestenberg@...il.com>
Cc:	Steve Rottinger <steve@...tek.com>, linux-kernel@...r.kernel.org
Subject: Re: splice methods in character device driver

On Sat, Jun 06 2009, Leon Woestenberg wrote:
> Hello Jens,
> 
> in the spirit of splice-and-dice I continue asking questions until I grasp this.
> 
> On Mon, May 11, 2009 at 9:22 PM, Jens Axboe<jens.axboe@...cle.com> wrote:
> > So if your design is allocating the pages in the ->splice_read()
> > handler and initiating IO to these pages, then you need to provide a
> > suitable ->confirm() hook that can wait on this IO to complete if
> > needed.
> 
> When the driver's splice_read() is called, the kernel wants the driver to
> allocate pages and later check that they are filled with data through the
> confirm() hook. Is that correct?

Correct.

> How can I pass information from the splice_read(), which spawns a hardware
> DMA to the pages in my case, to the confirm() hook which is called at some
> (random) time in the future?

There's a ->private for each pipe_buffer, so you can pass along info on
a per-page granularity.

-- 
Jens Axboe

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