Re: finding out the value of HZ from userspace

From: Randy.Dunlap
Date: Wed Mar 31 2004 - 16:50:07 EST

On Sun, 21 Mar 2004 10:58:20 +1100 Peter Williams wrote:

| Albert Cahalan wrote:
| > On Sat, 2004-03-20 at 04:56, Arjan van de Ven wrote:
| >
| >>On Tue, Mar 16, 2004 at 11:14:59AM -0500, Albert Cahalan wrote:
| >>
| >>>>there is one. Nothing uses it
| >>>>(sysconf() provides this info)
| >>>
| >>>If you have a recent glibc on a recent kernel, it might.
| >>>You could also get a -1 or a supposed ABI value that
| >>>has nothing to do with the kernel currently running.
| >>>The most reliable way is to first look around on the
| >>>stack in search of ELF notes, and then fall back to
| >>>some horribly gross hacks as needed.
| >>
| >>eh sysconf() is the nice way to get to the ELF notes
| >>instead of having to grovel yourself.
| >
| >
| > Unless there is some hidden feature that lets
| > me specify the ELF note number directly, no way.
| >
| > The sysconf(_SC_CLK_TCK) call does not return an
| > error code when used on a 2.2.xx i386 kernel.
| > You get an arbitrary value that fails for ARM,
| > Alpha, and any system with modified HZ.
| As Linux is supposed to be POSIX compliant this is a bug and should be
| fixed.

My understanding (from a few years back) is that Linux is POSIX
if/when/where it makes sense, but not necessarily POSIX-just-to-be-POSIX.

"You can't do anything without having to do something else first."
-- Belefant's Law
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