[PATCH 09/10] libbsd.txt: Describe current state of WLAN.

Christian Mauderer christian.mauderer at embedded-brains.de
Thu Nov 9 08:17:51 UTC 2017

Am 09.11.2017 um 09:03 schrieb Chris Johns:
> On 09/11/2017 17:41, Christian Mauderer wrote:
>> currently there is still no rc.conf support. I took a look at it and
>> found out that I can't do it in the scope of the project. Therefore I
>> only added a note regarding this in the "known restrictions".
> Hmmm.

Yes, I know. Not really a solution. But please keep in mind that WiFi on
RTEMS is a work in progress. It can't be expected that from "no WiFi" to
"WiFi completely integrated" is only one step.

>> In FreeBSD, the creation of such devices would be handled by rc.conf
>> lines like
>>     wlans_rtwn0="wlan0"
>>     ifconfig_wlan0="DHCP"
>> It wouldn't be a great problem to parse such lines in rc.conf and call a
>> matching ifconfig command. 
> The rc.conf API we have should be able to handle something like that or it
> should be close.

I would have expected that too. Therefore: That one shouldn't be a big

>> But there is a problem due to the nature of
>> the rtwn0 device: It's an USB device. Due to that, it isn't there right
>> from the start. Depending on quite a number of conditions it will appear
>> sooner or later during the startup or - in the worst case - a user could
>> plug it after a few minutes of run time.
> Understood, enumeration takes time.
>> Please correct me if I'm wrong but as far as I know, the rc.conf support
>> in RTEMS currently is only executed once during start without
>> remembering any configuration for later use. The source can be either a
>> file or a string.
> Is rc.conf run more than once in FreeBSD? I know the `service` command uses it
> to know if a service is enabled, ie onestart etc. Is there something else?

I'm no FreeBSD user and I only have a rough knowledge about how things
are done there. From my Linux-point-of-view I would expect that there is
something similar to udev that does some actions as soon as a new device
is discovered. I just somehow expected that in case of a network device
this action on FreeBSD would be to look in the rc.conf whether there is
something to do with this device. But I can be wrong too.

>> With that in mind, I would expect that roughly the following would be
>> necessary for that implementation:
>> - To handle dynamically added WiFi and network devices through rc.conf,
>> either the complete rc.conf string or at least the information from the
>> wlans_xxx and ifconfig_xxx lines has to be kept somewhere for later use.
>> - Some kind of handler or daemon for detecting new USB devices would be
>> necessary. As far as I know, there is currently no such thing. The only
>> other application with dynamic device detection that I know of is the
>> media listener. But I think that is on block device level and not on the
>> USB level.
> I am confused about the way FreeBSD does this. I did not think rc.conf is rerun
> at all. As I said it is parsed by lots of things. We should follow the same
> model if that is feasible. If you could determine what FreeBSD does it would go
> a long way to knowing which path is the best path to follow.

Like said above, I would expect rc.conf to get re-parsed for new network
devices. But I'm not sure about that.

We can't follow that model exactly. As far as I know, we can have at
least two sources for our rc.conf: Either a string or a file. In case of
the string, we would have to copy that string so we can parse it later
again. For big configs, that might wouldn't be the best idea.

A better solution could be to prepare some lists with configurations for
devices. These lists could then be used on demand.

>> I would have liked to add that integration to have a clean solution.
> I agree on needing a clean solution but it is not clear yet what that is.
>> But
>> like I said, there isn't enough free budget left in that project to do
>> it. I really hope that we can find some time and budget for it in the
>> future.
> I respect and thank you for being open about this. I view getting a suitable
> solution for rc.conf is important for the project because this stuff is
> complicated to get working. I have raised rc.conf before and I had hoped it was
> understood we need to support it. It is crazy to require users to have some
> parts in rc.conf and other parts in complex fragile custom code to make this
> stack work. This has been a valid criticism of RTEMS for years and I would like
> to see us address it.

Agreed. I would prefer the configuration in rc.conf too. But again: WiFi
in RTEMS is (from my point of view) still a work in progress.

> Could you please determine what rc.conf work is needed and document it in a
> ticket? I feel you are best to do this since you are across the code in detail.

Good point. I'll create a ticket.

> Chris

Kind Regards


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Christian Mauderer
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