linux-kernel - Rich man's version of AIO on Linux 2.6.x?

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Date:	Fri, 22 May 2009 02:59:53 +0200
From:	Leon Woestenberg <leon.woestenberg@...il.com>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	devel@...uxdriverproject.org
Subject: Rich man's version of AIO on Linux 2.6.x?

Hello,

On the state-of-art of asynchronous I/O in Linux. I understand we have
full support for AIO in the Linux 2.6.x kernel but I cannot find how
to use it from user space.

I would like to exploit AIO in hardware and the device driver for it,
by keeping the hardware performing I/O at all times (no setup latency
between requests by allowing multiple
I/O requests to be queued in hardware). Note this is a character
device, not a filesystem.

I implemented aio_read() and aio_write() on my character device
interface, but it's never been called; read() and write() is called
instead.

>From "Understanding the Linux kernel, 3rd edition" I read that glibc
indeed implements aio_read() and friends itself, not through the
kernel AIO syscalls.

<Quote>
Essentially, the aio_read( ) or aio_write( ) library function clones
the current process and lets the child invoke the synchronous read( )
or write( ) system calls; However, this "poor man's" version of the
POSIX functions is significantly slower than a version that uses a
kernel-level implementation of asynchronous I/O.
<End Quote>

I am looking for a rich man's way to use the kernel functionality;
essentially I want my drivers aio_read and aio_write ops to be called.

Regards,
-- 
Leon
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