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    SubjectRe: sysconf (was Re: RLIM_INFINITY inconsistency between archs)

    H. Peter Anvin writes:
    > [Theodore Y. Ts'o writes]

    >> Linus is right, no major structural change is necessary. For example,
    >> here's a very short patch necessary to support __SC_CLK_TCK (which is
    >> probably the most interesting of the sysconf() variables as far as I'm
    >> concerned.) It's only a 5-line patch. (See below)
    > I don't think we want to do this! IMO, HZ should not get exported to
    > user space *AT ALL*. Instead, for the few interfaces that need it,
    > we'll export a "user space HZ" (USER_HZ) which is fixed. No need for
    > a kernel hack. When we support nonstandard values for HZ, we need to
    > fix the few interfaces that actually export jiffies values to convert
    > from "user jiffies" to real jiffies.

    We should export the "user jiffies". Eventually this _may_ become a
    real per-arch constant, but for now it is not. For now it is just HZ,
    and you can't stop people from adjusting it. User-space already has
    to hack around the lack of __SC_CLK_TCK, and I assure you that it is
    very gross... the procps code could make you vomit.

    The only promise needed is that __SC_CLK_TCK match the units used
    in /proc and tick-based system call(s). Even if HZ were to die, we'd
    still need some sort of unit to represent stuff in /proc. That unit
    is the one that userspace needs.

    Suggestion for glibc NGROUPS_MAX problem: in the typical way of
    hacking around lack of kernel support, have glibc run a setuid-root
    executable that reads kernel memory. Use the file to
    seek out a suitable spot. You get bonus points for using statistical
    methods or arch-specific disassembly of the executable code.

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