Query on usage of Netlink

Query on usage of Netlink

[Kumar SANGHVI]

Hi All,

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.

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.

For this, we want to know what Netlink message type should we use?
Should we use some existing Netlink type? Will there be any risk of
getting other messages (the ones not sent by our driver) if using
existing Netlink message type? For e.g. if we use the existing type
NETLINK_ROUTE then, user-space may un-necessary receive netlink notification
for route changes.

Or should we define a custom Netlink type in include/linux/netlink.h?

Thank you for suggestions.

Best regards,
Kumar.

Re: Query on usage of Netlink

[Rémi Denis-Courmont]

On Fri, 8 Oct 2010 14:21:28 +0530, Kumar SANGHVI
<kumar.sanghvi@stericsson.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?

> 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)?

-- 
Rémi Denis-Courmont
http://www.remlab.net
http://fi.linkedin.com/in/remidenis

Re: Query on usage of Netlink

[Kumar SANGHVI]

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@stericsson.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.