Re: device_attach(9) and driver initialization

On 4/7/12 8:15 AM, Konstantin Belousov wrote:
> On Sat, Apr 07, 2012 at 10:04:59AM -0500, Nathan Whitehorn wrote:
>> On 04/07/12 07:50, Konstantin Belousov wrote:
>>> Hello,
>>> there seems to be a problem with device attach sequence offered by newbus.
>>> Basically, when device attach method is executing, device is not fully
>>> initialized yet. Also the device state in the newbus part of the world
>>> is DS_ALIVE. There is definitely no shattering news in the statements,
>>> but drivers that e.g. create devfs node to communicate with consumers
>>> are prone to a race.
>>>
>>> If /dev node is created inside device attach method, then usermode
>>> can start calling cdevsw methods before device fully initialized itself.
>>> Even more, if device tries to use newbus helpers in cdevsw methods,
>>> like device_busy(9), then panic occurs "called for unatteched device".
>>> I get reports from users about this issues, to it is not something
>>> that only could happen.
>>>
>>> I propose to add DEVICE_AFTER_ATTACH() driver method, to be called
>> >from newbus right after device attach finished and newbus considers
>>> the device fully initialized. Driver then could create devfs node
>>> in the after_attach method instead of attach. Please see the patch below.
>>>
>> Something like this would also be very useful for drivers that need to
>> interact across the device tree, if newbus called it only after all
>> drivers have been attached. Drivers that need to see other potentially
>> attached drivers now need to do some hacks with SYSINIT. Would it be
>> possible to do this? I don't think it changes the functionality you need.
> I am definitely fine with postponing a call further, but I am not sure
> how to define that point and how to implement your proposal. I am mostly
> thinking of the case of kld being loaded, since for compiled-in drivers,
> there is simply no usermode to make the havoc during attach.

no, Geom starts tasting disk devices as as soon as you make the device.

> For the boot time attachments, I am not sure when to declare the end.
> E.g. USB does asynchronous device discovery.
>
> Could you prototype a change that would do what you propose ?