Date: Fri, 28 Dec 2007 18:17:00 +0100 (CET) From: "Max Laier" <max.laier@tm.uka.de> To: "John Baldwin" <jhb@FreeBSD.org> Cc: arch@freebsd.org Subject: Re: kernel features MIB Message-ID: <43684.2001:6f8:12c8:1:21d:60ff:fe0c:1771.1198862220.squirrel@router.laiers.local> In-Reply-To: <200712271704.44796.jhb@FreeBSD.org> References: <200712271704.44796.jhb@FreeBSD.org>
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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. -- /"\ Best regards, | mlaier@freebsd.org \ / Max Laier | ICQ #67774661 X http://pf4freebsd.love2party.net/ | mlaier@EFnet / \ ASCII Ribbon Campaign | Against HTML Mail and News
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