Date: Sat, 7 Apr 2012 21:13:06 -0600 From: Warner Losh <imp@bsdimp.com> To: Nathan Whitehorn <nwhitehorn@FreeBSD.org> Cc: Konstantin Belousov <kostikbel@gmail.com>, current@FreeBSD.org, drivers@FreeBSD.org Subject: Re: device_attach(9) and driver initialization Message-ID: <BEDF914C-1202-4966-9357-9174ECC5C824@bsdimp.com> In-Reply-To: <4F80579B.4040205@freebsd.org> References: <20120407125056.GS2358@deviant.kiev.zoral.com.ua> <4F80579B.4040205@freebsd.org>
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On Apr 7, 2012, at 9:04 AM, 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 >=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. Well, there's a problem here. You never know that you've attached = everything, so you could never really call it. Many busses enumerate = asynchronously, so it may be hard to get the semantics that you desire = unless the two devices you want to coordinate are in the static part of = the tree. Warner
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