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

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Date:	Sat, 6 Jun 2009 23:25:49 +0200
From:	Leon Woestenberg <leon.woestenberg@...il.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Steve Rottinger <steve@...tek.com>, linux-kernel@...r.kernel.org
Subject: Re: splice methods in character device driver

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?

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?

static int splice_read(struct file *in, loff_t *ppos,
struct pipe_inode_info *pipe, size_t len, unsigned int flags)

static int alt_pipe_buf_confirm(struct pipe_inode_info *pipe,
struct pipe_buffer *buf)

Regards,
-- 
Leon
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