netdev - Re: Query on usage of Netlink

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Date:	Fri, 8 Oct 2010 16:01:44 +0530
From:	Kumar SANGHVI <kumar.sanghvi@...ricsson.com>
To:	Rémi Denis-Courmont <remi@...lab.net>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Srinidhi KASAGAR <srinidhi.kasagar@...ricsson.com>,
	Linus WALLEIJ <linus.walleij@...ricsson.com>,
	Sudeep DIVAKARAN <sudeep.divakaran@...ricsson.com>,
	Gulshan KARMANI <gulshan.karmani@...ricsson.com>
Subject: Re: Query on usage of Netlink

Hi Rémi Denis-Courmontt,

On Fri, Oct 08, 2010 at 12:14:44 +0200, Rémi Denis-Courmont wrote:
> 
> On Fri, 8 Oct 2010 14:21:28 +0530, Kumar SANGHVI
> <kumar.sanghvi@...ricsson.com> wrote:
> > We have a requirement where-in we want to communicate the status of
> > modem (whether modem is online or offline) from linux driver to
> > user-space components. So that user-space components stop sending data
> > to linux driver for communicating with modem, in case modem goes
> > offline.
> 
> Is the modem control state machine in kernel space, as for say, 802.11
> devices?
State machine to keep track of current modem state is in kernel driver.
Kernel driver can know when modem goes offline or when modem is back
online.

> > We have decided to use the netlink mechanism to achieve this. We intend
> > to send an integer value, defined in enum, to user-space indicating the
> > current modem status.
> (...)
> > Or should we define a custom Netlink type in include/linux/netlink.h?
> 
> Did you consider using kobject and uevents (which are internally running on
> top of Netlink)?
Yes. However, I believe kobject and uevents require some user-space
daamon like udev which can dispatch the specific uevents to user-space
apps. This user-space daemon then becomes something application
framework specific.
Another option is that user-space app itself open up a netlink socket of type
KOBJECT_UEVENT. But then, user-space will have to filter out
un-necessary uevents out of it. 

Best regards,
Kumar.
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