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    SubjectRe: sched_setaffinity usability
    Ingo Molnar wrote:
    > * Linus Torvalds <> wrote:
    >>sysconf() is a user-level implementation issue, and so is something
    >>like "number of CPU's". Damn, the simplest way to do it is as a
    >>environment variable, for christ sake! Just make a magic environment
    >>variable called __SC_ARRAY, and make it be some kind of binary
    >>encoding if you worry about performance.
    > i am not arguing for any sysconf() support at all - it clearly belongs
    > into glibc. Just doing 'man sysconf' shows that it should be in
    > user-space. No argument about that.
    > But how about the original issue Ulrich raised: how does user-space
    > figure out the NR_CPUS value supported by the kernel? (not the current #
    > of CPUs, that can be figured out using /proc/cpuinfo)
    > one solution would be what you suggest: to build some sort of /etc/info
    > file that glibc can access, which file is build during the kernel build
    > and contains the necessary constants. One problem with this approach is
    > that a user could boot via any arbitrary kernel, how does glibc (or even
    > a supposed early-init info-setup mechanism) know what info belongs to
    > which kernel? Kernel version numbers are not required to be unique. A
    > single non-modular bzImage can be used to have a fully working
    > userspace. Right now the kernel and glibc is isolated pretty much and
    > this gives us flexibility.

    Let the compile create that info file. Then handle it much like a module,
    except that it is a "module" without any code.
    I.e. copy it to /lib/modules/<kernelversion> if installing modules,
    or stuff the file into the initrd if making an initrd.

    Now it is in a place specific to the kernel, where a library can find it.

    Helge Hafting

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