Re: device_attach(9) and driver initialization

On Apr 7, 2012, at 3:34 PM, Julian Elischer wrote:

> 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.
>>>>=20
>>>> 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.
>>>>=20
>>>> 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.
>>>>=20
>>> 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.
>=20
> no, Geom starts tasting disk devices as as soon as you make the =
device.

Which is why the typical way to cope with this is to not create the =
device until you are ready to service requests for it.  The other method =
is to have a flag that's only set after you actually are ready that the =
open routine can check and keep people out of the rest of the devsw =
functions by returning ENXIO or similar error.

Warner

>> For the boot time attachments, I am not sure when to declare the end.
>> E.g. USB does asynchronous device discovery.
>>=20
>> Could you prototype a change that would do what you propose ?
>=20
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>=20
>=20

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