Re: NGROUPS_MAX in linux 2.6.3+

[Andreas Jaeger <aj at suse dot de>]

Tim Hockin <thockin@sun.com> writes:

> Replying to my own mail.
>
> On Thu, Feb 19, 2004 at 01:20:25PM -0800, Tim Hockin wrote:
>> 1.  Linux does not have a way to report these "constants" to libc.  It is a
>> constant for a given kernel, but not necessarily across kernels.  I am going
>> to try to find a good way to do that.  Watch for a patch, unless Linus tells
>> me to buzz off.
>
> Patch is here.  Linux will now expose a sysctl to read it's idea of
> NGROUPS_MAX.
>
> Can I get an ACK or NACK on this please, so I can rework it or mark it as
> done?

Let me reply to libc-alpha so that it has a chance to be seen.

The problem I see with your patch, is that there seems to be no
fallback for the case where you compile this with kernel headers that
define KERN_NGROUPS_MAX but do run it on an older kernel.  Check how
we do this with kernel-features.h,

Andreas

Index: sysdeps/unix/sysv/linux/sysconf.c
===================================================================
RCS file: /cvs/glibc/libc/sysdeps/unix/sysv/linux/sysconf.c,v
retrieving revision 1.9
diff -u -u -r1.9 sysconf.c
--- sysdeps/unix/sysv/linux/sysconf.c	27 Mar 2003 17:55:08 -0000	1.9
+++ sysdeps/unix/sysv/linux/sysconf.c	24 Feb 2004 00:11:08 -0000
@@ -20,6 +20,7 @@
 #include <sysdep.h>
 #include <time.h>
 #include <unistd.h>
+#include <sys/sysctl.h>
 
 static long int posix_sysconf (int name);
 
@@ -43,6 +44,20 @@
 	int r;
 	r = INTERNAL_SYSCALL (clock_getres, err, 2, CLOCK_MONOTONIC, &ts);
 	return INTERNAL_SYSCALL_ERROR_P (r, err) ? -1 : 1;
+      }
+#endif
+
+#ifdef KERN_NGROUPS_MAX
+    case _SC_NGROUPS_MAX:
+      {
+        int name[] = { CTL_KERN, KERN_NGROUPS_MAX };
+        int ngroups_max;
+        int ngroups_max_len = sizeof (ngroups_max);
+
+        if (__sysctl (name, sizeof (name) / sizeof (*name),
+                      &ngroups_max, &ngroups_max_len, 0, 0) < 0)
+            return -1;
+        return ngroups_max;
       }
 #endif
 

-- 
 Andreas Jaeger, aj@suse.de, http://www.suse.de/~aj
  SuSE Linux AG, Maxfeldstr. 5, 90409 Nürnberg, Germany
   GPG fingerprint = 93A3 365E CE47 B889 DF7F  FED1 389A 563C C272 A126

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