linux-kernel - Re: Best method for sending messages to user space?

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Date:	Tue, 21 Oct 2008 13:16:04 -0700
From:	"Dan Williams" <dan.j.williams@...el.com>
To:	"Timur Tabi" <timur@...escale.com>
Cc:	linux-kernel@...r.kernel.org,
	"Kumar Gala" <kumar.gala@...escale.com>
Subject: Re: Best method for sending messages to user space?

On Tue, Oct 21, 2008 at 12:43 PM, Timur Tabi <timur@...escale.com> wrote:
> Dan Williams wrote:
>
>> I really like the sysfs_notify() approach that Neil Brown has put
>> together for delivering md-raid events.
>
> Is there any documentation for sysfs_notify?  It doesn't appear to do anything
> whenever I call it.
>

It simply allows you to write an event loop in userspace using a sysfs
attribute file descriptor.  Pseudo-example:

fd = open("/sys/block/md0/md/array_state");
do {
	read(buf, fd, len);
	act_on_message(buf);
	select(...); /* wait for next sysfs_notify event */
	lseek(fd, 0, SEEK_SET); /* seek back so we can read the new state */
} while (1);
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