Date: Fri, 28 Dec 2007 13:00:28 -0500 From: John Baldwin <jhb@freebsd.org> To: "Max Laier" <max.laier@tm.uka.de> Cc: arch@freebsd.org Subject: Re: kernel features MIB Message-ID: <200712281300.28899.jhb@freebsd.org> In-Reply-To: <43684.2001:6f8:12c8:1:21d:60ff:fe0c:1771.1198862220.squirrel@router.laiers.local> References: <200712271704.44796.jhb@FreeBSD.org> <43684.2001:6f8:12c8:1:21d:60ff:fe0c:1771.1198862220.squirrel@router.laiers.local>
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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
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