linux-kernel - Re: [PATCH] dvb: Allow MAC addresses to be mapped to stable device names with udev

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Message-ID: <8474.1540982182@warthog.procyon.org.uk>
Date:   Wed, 31 Oct 2018 10:36:22 +0000
From:   David Howells <dhowells@...hat.com>
To:     Sean Young <sean@...s.org>
Cc:     dhowells@...hat.com,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Michael Krufky <mkrufky@...uxtv.org>,
        Brad Love <brad@...tdimension.cc>, mchehab@...nel.org,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dvb: Allow MAC addresses to be mapped to stable device names with udev

Sean Young <sean@...s.org> wrote:

> > > Devices have a MAC address available, which is printed during boot:
> 
> Not all dvb devices have a mac address.

How do I tell?  If it's all zeros it's not there?

> Devices without a mac address shouldn't have a mac_dvb sysfs attribute,
> I think.

I'm not sure that's possible within the core infrastructure.  It's a class
attribute set when the class is created; I'm not sure it can be overridden on
a per-device basis.

Possibly the file could return "" or "none" in this case?

> The dvb type and dvb adapter no is already present in the device name,
> I'm not sure why this needs duplicating.

They can be used with ATTR{} in udev rules.  I'm not clear that the name can.

> With this patch, with a usb Hauppauge Nova-T Stick I get:
> ...
> ==> /sys/class/dvb/dvb0.demux0/dvb_mac <==
> 00:00:00:00:00:00

I can't say why that happens.  I don't have access to this hardware.  Should
it have a MAC address there?  Is the MAC address getting stored in
dvbdev->adapter->proposed_mac?  Maybe it's not getting read - on the card I
use it's read by the cx23885 driver... I think...  The nova-t-usb2.c file
doesn't mention proposed_mac.

David