Date: Sat, 7 Apr 2012 18:15:14 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Nathan Whitehorn <nwhitehorn@freebsd.org> Cc: current@freebsd.org, drivers@freebsd.org Subject: Re: device_attach(9) and driver initialization Message-ID: <20120407151514.GW2358@deviant.kiev.zoral.com.ua> In-Reply-To: <4F80579B.4040205@freebsd.org> References: <20120407125056.GS2358@deviant.kiev.zoral.com.ua> <4F80579B.4040205@freebsd.org>
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--CN5+qz79j8MMBHjt Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable 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 newbu= s. > >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. > > >=20 > Something like this would also be very useful for drivers that need to=20 > interact across the device tree, if newbus called it only after all=20 > drivers have been attached. Drivers that need to see other potentially=20 > attached drivers now need to do some hacks with SYSINIT. Would it be=20 > 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. 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 ? --CN5+qz79j8MMBHjt Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (FreeBSD) iEYEARECAAYFAk+AWgIACgkQC3+MBN1Mb4hlswCghMA1W9QGOErIQUXaukNrBxIb D74AoJ9vcwS2c3f5JPGkfU3zdhrqe7zP =v3zv -----END PGP SIGNATURE----- --CN5+qz79j8MMBHjt--
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