[LEDE-DEV] [PATCH v1 1/2] base-files, mac80211, broadcom-wl: plug-and-play wifi detection

Matthias Schiffer mschiffer at universe-factory.net
Sat Oct 8 10:29:13 PDT 2016

On 10/08/2016 07:13 PM, Christian Lamparter wrote:
> On Saturday, October 8, 2016 6:04:09 PM CEST Matthias Schiffer wrote:
>> On 10/08/2016 05:41 PM, Christian Lamparter wrote:
>>> On Friday, October 7, 2016 8:29:30 PM CEST Matthias Schiffer wrote:
>>>> On 10/07/2016 08:10 PM, Christian Lamparter wrote:
>>>>> Currently, the wifi detection script is executed as part of
>>>>> the (early) boot process. Pluggable wifi USB devices, which
>>>>> are inserted at a later time are not automatically
>>>>> detected and therefore they don't show up in LuCI.
>>>>> A user has to deal with wifi detection manually, or restart
>>>>> the router.
>>>>> [...]
>>>>> ---
>>>>> We would like to hear, if these changes work with broadcom-wl.
>>>>> (Felix removed the hostap, so this isn't included anymore).
>>>>> trap and lock are part of the default busybox setup.
>>>> Hi,
>>>> it would be great to remove the direct write of /etc/config/wireless
>>>> completely, as it won't lock against other users of UCI that modify the
>>>> wireless config. IMO, it should just use UCI to modify the configuration as
>>>> everything else does.
>>> Well, What's the situation with ECE and configd? I didn't want to touch it
>>> since you plan to move away from the config files and replace them with
>>> json. 
>> There isn't a concrete plan to integrate ECE with LEDE yet (there are still
>> some TODOs, and it will need to be discussed further with the LEDE
>> community). It will provide a bidirectional UCI mapping; this means as long
>> as the uci CLI and similar tools are used, most things should just continue
>> work with ECE.
> Ok. But how would the /etc/config/wireless have worked? As it just produced a
> file and bypassed all the uci CLI and similar tools. Did you setup file
> notifications to check if something as modified in /etc/config/ run uci to
> import it or sth. like that? (Because that was why I contacted you earlier :) )

Converting that script to the UCI CLI was still a TODO for making this
work. So far, I haven't even finished the binding code itself (I've been
working on other projects during the last weeks), and haven't had a closer
look at all UCI users yet to look for potential issues. I plan to return to
working on ECE soon.

>>> Note: the "> /dev/null" for uci calls were added just in case someone still
>>> has the old /etc/init.d/boot and to not write garbage into /e/c/wireless.
>>> Note2: I've also changed the "plug-and-play wifi" patch and removed the
>>> /tmp/wireless.tmp step. But we still need proper locking. 
>>> (That said, I would like to move the locking to the mac80211.sh / broadcom.sh
>>> detect functions, is everyone fine with that?)
>> Makes sense to me (maybe we can further factor out common parts of
>> mac80211.sh and broadcom.sh?).
> I don't think that's within the scope of this series :-D. Also, I don't have
> any  broadcom devices... 
>> Note that you don't need any locking in the hotplug handlers anyways, they are
>> always run sequentially.
> I moved the locking to detect_mac80211 and detect_broadcom. 
> A user might still want to run "wifi detect" (out of habit?) and that
> could race with hotplug event .
> As for procd:
> Can you tell me where this serialization happens or how it works?
> I've looked into this earlier and found that procd uses the hotplug-call
> in hotplug.json to run all the scripts under /etc/hotplug.d/%SUBSYSTEMS%.
> I've looked up handle_exec (which is used to run hotplug-call)
> and found execvp [0]. The thing with execvp is that it fully replaces
> the current thread with the new program it is supposed to execute
> (it never returns, unless it fails before it jumps to the new program).
> So procd needs to fork() before it can run hotplug-call and this is
> done in queue_next [1].
> However, if procd is supposed to serialize these calls, it will
> need to use some sort of wait() or waitpid() to wait for the
> forked processes to finish. Since there is no wait()/waitpid() in 
> there, the hotplug-call can run concurrently.

queue_proc_cb() is run as soon as the previous hotplug-call is finished
(the wait is hidden behind uloop), which will then call queue_next() to
handle the next hotplug event.

> (I know that the event messages from the kernel to procd are indeed
> serialized by the netlink message interface.)
> so, what is wrong here?
> Regards,
> Christian
> [0] <https://git.lede-project.org/?p=project/procd.git;a=blob;f=plug/hotplug.c;h=85959155634f1a6a9ada11c7045601885a0abad8;hb=72f63807b3644ef7b8ab9025a02d7f509f39ad14#l204>
> [1] <https://git.lede-project.org/?p=project/procd.git;a=blob;f=plug/hotplug.c;h=85959155634f1a6a9ada11c7045601885a0abad8;hb=72f63807b3644ef7b8ab9025a02d7f509f39ad14#l347>

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