From owner-freebsd-arch@FreeBSD.ORG Fri Dec 28 19:40:06 2007 Return-Path: Delivered-To: arch@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 9F3A116A418 for ; Fri, 28 Dec 2007 19:40:06 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from speedfactory.net (mail6.speedfactory.net [66.23.216.219]) by mx1.freebsd.org (Postfix) with ESMTP id 357F613C474 for ; Fri, 28 Dec 2007 19:40:06 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from server.baldwin.cx (unverified [66.23.211.162]) by speedfactory.net (SurgeMail 3.8q) with ESMTP id 226422916-1834499 for multiple; Fri, 28 Dec 2007 14:42:04 -0500 Received: from localhost.corp.yahoo.com (john@localhost [127.0.0.1]) (authenticated bits=0) by server.baldwin.cx (8.13.8/8.13.8) with ESMTP id lBSJdg7G064138; Fri, 28 Dec 2007 14:39:43 -0500 (EST) (envelope-from jhb@freebsd.org) From: John Baldwin To: "Max Laier" Date: Fri, 28 Dec 2007 13:00:28 -0500 User-Agent: KMail/1.9.6 References: <200712271704.44796.jhb@FreeBSD.org> <43684.2001:6f8:12c8:1:21d:60ff:fe0c:1771.1198862220.squirrel@router.laiers.local> In-Reply-To: <43684.2001:6f8:12c8:1:21d:60ff:fe0c:1771.1198862220.squirrel@router.laiers.local> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200712281300.28899.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH authentication, not delayed by milter-greylist-2.0.2 (server.baldwin.cx [127.0.0.1]); Fri, 28 Dec 2007 14:39:43 -0500 (EST) X-Virus-Scanned: ClamAV 0.91.2/5278/Fri Dec 28 11:55:36 2007 on server.baldwin.cx X-Virus-Status: Clean X-Spam-Status: No, score=-4.4 required=4.2 tests=ALL_TRUSTED,AWL,BAYES_00 autolearn=ham version=3.1.3 X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on server.baldwin.cx Cc: arch@freebsd.org Subject: Re: kernel features MIB X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 28 Dec 2007 19:40:06 -0000 On Friday 28 December 2007 12:17:00 pm Max Laier wrote: > > Am Do, 27.12.2007, 23:04, schrieb John Baldwin: > > One of the things we have at work is a kern.features sysctl MIB that > > contains > > nodes to indicate if a named feature is present. For example, on i386 we > > have kern.features.pae and we auto enable -DPAE for kernel modules if the > > currently running kernel is using PAE using that sysctl. > > > > One of the patches I want to commit soon is support for handling > > shm_open/shm_unlink directly in the kernel via swap-backed VM objects (the > > long-heralded memfd stuff). I would like to have the sysctl MIB so that > > libc's for older releases (e.g. libc.so.6) could use the syscalls if they > > are > > available so that shm segments are shared between compat apps (e.g. 4.x or > > 6.x) and up-to-date apps. > > > > At work we don't have a pretty API for this at all, but I'm thinking for > > FreeBSD we can do this: > > > > FEATURE(foo, "description of foo") > > > > which is a macro to create the 'kern.features.foo' node and set it to 1. > > Then > > we could have a routine in libc: > > > > int feature_present(const char *name); > > > > That returns a boolean to indicate if a given feature is present or not by > > invoking sysctlbyname(3), etc. > > > > Any objections to the idea? > > Sounds like a good idea indeed. What about modules, though? Would it > make sense to have something ident/strings parseable in the .kld to > identify features provided by that module? feature_present (or > _available) could search the default module paths and return which module > needs to be loaded. This could depend on FEATURE(kld, ...) and maybe > kern.securelevel. You could have a userland tool that parses the linker set for sysctl's and uses the name of the symbol to figure this out if that was desired. Modules already have the MODULE_DEPEND stuff available that could be used, but I'm thinking about things that aren't in modules. -- John Baldwin