Re: [PATCH] rfkill: allocate static minor

[Marcel Holtmann]

Hi Greg,

>> udev has a feature of creating /dev/<node> device-nodes if it finds
>> a devnode:<node> modalias. This allows for auto-loading of modules that
>> provide the node. This requires to use a statically allocated minor
>> number for misc character devices.
>> 
>> However, rfkill uses dynamic minor numbers and prevents auto-loading
>> of the module. So allocate the next static misc minor number and use
>> it for rfkill.
> 
> As rfkill has been around for a long time, what new use case is needing
> to auto-load this based on a major number?

we have bug reports from iwd users where it fails opening /dev/rfkill. Since iwd can be actually started before the WiFi hardware is fully probed and all its drivers are loaded, we have a race-condition here if rfkill is not capable of auto-loading.

The difference is really that iwd is a fully self-contained WiFi daemon compared to wpa_supplicant which is just some sort of helper. iwd is fully hot plug capable as well compared to wpa_supplicant. It looks like this is exposing the race condition for our users. Frankly, we should have fixed rfkill a long time ago when we fixed uinput, uhid etc, but seems we forgot it. I assume mainly because it magically got loaded in time by some module dependencies.

Regards

Marcel