From owner-freebsd-new-bus@FreeBSD.ORG Tue Jan 17 18:09:33 2006 Return-Path: X-Original-To: freebsd-new-bus@freebsd.org Delivered-To: freebsd-new-bus@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 2879216A42B; Tue, 17 Jan 2006 18:09:33 +0000 (GMT) (envelope-from john@baldwin.cx) Received: from speedfactory.net (mail6.speedfactory.net [66.23.216.219]) by mx1.FreeBSD.org (Postfix) with ESMTP id 365A943D58; Tue, 17 Jan 2006 18:09:32 +0000 (GMT) (envelope-from john@baldwin.cx) Received: from server.baldwin.cx (unverified [66.23.211.162]) by speedfactory.net (SurgeMail 3.5b3) with ESMTP id 6283689 for multiple; Tue, 17 Jan 2006 13:08:07 -0500 Received: from localhost (john@localhost [127.0.0.1]) by server.baldwin.cx (8.13.4/8.13.4) with ESMTP id k0HI9Ci0039363; Tue, 17 Jan 2006 13:09:25 -0500 (EST) (envelope-from john@baldwin.cx) From: John Baldwin To: freebsd-new-bus@freebsd.org Date: Tue, 17 Jan 2006 13:08:40 -0500 User-Agent: KMail/1.9.1 References: <200601061401.57308.john@baldwin.cx> In-Reply-To: <200601061401.57308.john@baldwin.cx> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200601171308.41539.john@baldwin.cx> X-Virus-Scanned: ClamAV 0.87.1/1244/Tue Jan 17 03:46:07 2006 on server.baldwin.cx X-Virus-Status: Clean X-Spam-Status: No, score=-1.4 required=4.2 tests=ALL_TRUSTED autolearn=failed version=3.1.0 X-Spam-Checker-Version: SpamAssassin 3.1.0 (2005-09-13) on server.baldwin.cx X-Server: High Performance Mail Server - http://surgemail.com r=1653887525 Cc: dfr@freebsd.org Subject: Re: Patch to prevent cycles in the devclass tree X-BeenThere: freebsd-new-bus@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: FreeBSD's new-bus architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 17 Jan 2006 18:09:33 -0000 On Friday 06 January 2006 14:01, John Baldwin wrote: > I have been doing some work recently to make the ACPI and OFW > (OpenFirmware) PCI bus drivers inherit from the PCI bus driver. As part of > this I've run into an issue because the subclass drivers (ACPI PCI and OFW > PCI) use the same name "pci" as the superclass. They do this so that they > can override the superclass when a "pci" device is added as a child of a > "pcib" device. The problem I ran into is that when the subclass was > registered, it called devclass_find_internal() with the parentname set to > "pci". This caused the "pci" devclass to set its dc->parent member to > point to itself. Thus, if in device_probe_child() we didn't find a > suitable driver in the first pass of the for loop, we'd keep looping > forever and hang during boot. > > This is the fix I'm currently using but I was curious about feedback on it. > It only checks to make sure the a devclass doesn't add itself as a parent, > it doesn't walk up hierarchy to avoid a cycle completely: > > --- //depot/vendor/freebsd/src/sys/kern/subr_bus.c 2005/10/04 22:25:30 > +++ //depot/user/jhb/acpipci/kern/subr_bus.c 2006/01/04 21:32:26 > @@ -781,7 +781,17 @@ > > bus_data_generation_update(); > } > - if (parentname && dc && !dc->parent) { > + > + /* > + * If a parent class is specified, then set that as our parent so > + * that this devclass will support drivers for the parent class as > + * well. If the parent class has the same name don't do this though > + * as it creates a cycle that can trigger an infinite loop in > + * device_probe_child() if a device exists for which there is no > + * suitable driver. > + */ > + if (parentname && dc && !dc->parent && > + strcmp(classname, parentname) != 0) { > dc->parent = devclass_find_internal(parentname, 0, FALSE); > } > > @@ -1240,6 +1250,7 @@ > void > devclass_set_parent(devclass_t dc, devclass_t pdc) > { > + KASSERT(dc != pdc, ("%s: loop", __func__)); > dc->parent = pdc; > } > > The other possible direction is to rename the subclasses to not use the > same name ("pci"), but doing that actually involves a fair bit of work as > it means teaching the various pcib drivers to create acpi_pci child devices > rather than pci child devices, etc. Comments, flames, etc.? -- John Baldwin <>< http://www.baldwin.cx/~john/ "Power Users Use the Power to Serve" = http://www.FreeBSD.org