BSD 4_2 release

[unix-history] / usr / src / ucb / gprof / hertz.c

#ifndef lint
   static      char *sccsid = "@(#)hertz.c     1.1 (Berkeley) 1/11/83";
#endif lint

   /*
    *  discover the tick frequency of the machine
    */
#include <nlist.h>
#include <stdio.h>

struct nlist    nl[] =  {{"_hz"},       /* clock ticks per second */
                        {0}};

hertz()
{
   int         kmem;                   /* file descriptor for /dev/kmem */
   long        lseek();
   long        seeked;                 /* return value from lseek() */
   long        hz;                     /* buffer for reading from system */
   int         red;                    /* return value from read() */
   int         closed;                 /* return value from close() */

#   define      VMUNIX  "/vmunix"       /* location of the system namelist */
   nlist(VMUNIX, nl);
   if (nl[0].n_type == 0) {
       fprintf(stderr, "no %s namelist entry for _hz\n", VMUNIX);
       return 0;
   }
#   define      KMEM    "/dev/kmem"     /* location of the system data space */
   kmem = open(KMEM, 0);
   if (kmem == -1) {
       perror("hertz()");
       fprintf(stderr, "open(\"%s\", 0)", KMEM);
       return 0;
   }
   seeked = lseek(kmem, nl[0].n_value, 0);
   if (seeked == -1) {
       fprintf(stderr, "can't lseek(kmem, 0x%x, 0)\n", nl[0].n_value);
       return 0;
   }
   red = read(kmem, &hz, sizeof hz);
   if (red != sizeof hz) {
       fprintf(stderr, "read(kmem, 0x%x, %d) returned %d\n",
               &hz, sizeof hz, red);
       return 0;
   }
   closed = close(kmem);
   if (closed != 0) {
       perror("hertz()");
       fprintf(stderr, "close(\"%s\")", KMEM);
       return 0;
   }
   return hz;
}