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

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Date:	Tue, 21 Oct 2008 13:42:42 -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 1:23 PM, Timur Tabi <timur@...escale.com> wrote:
> Dan Williams wrote:
>
>> 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);
>
> I meant from the kernel side.  I added a call to sysfs_notify(), and I didn't
> see any sysfs entries being created, so I presume I need to set up sysfs before
> I call sysfs_notify(), but I can't figure out what that setup is.
>

sysfs_notify() will not create any files it only operates on
pre-existing attributes created via kobject_{init_and_}add().  See:
http://lxr.linux.no/linux+v2.6.27/drivers/md/md.c#L3473
http://lxr.linux.no/linux+v2.6.27/drivers/md/md.c#L3761
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