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Annotation of 42BSD/ucb/gprof/hertz.c, revision 1.1.1.1

1.1       root        1: #ifndef lint
                      2:     static     char *sccsid = "@(#)hertz.c     1.1 (Berkeley) 1/11/83";
                      3: #endif lint
                      4: 
                      5:     /*
                      6:      * discover the tick frequency of the machine
                      7:      */
                      8: #include <nlist.h>
                      9: #include <stdio.h>
                     10: 
                     11: struct nlist   nl[] =  {{"_hz"},       /* clock ticks per second */
                     12:                         {0}};
                     13: 
                     14: hertz()
                     15: {
                     16:     int                kmem;                   /* file descriptor for /dev/kmem */
                     17:     long       lseek();
                     18:     long       seeked;                 /* return value from lseek() */
                     19:     long       hz;                     /* buffer for reading from system */
                     20:     int                red;                    /* return value from read() */
                     21:     int                closed;                 /* return value from close() */
                     22: 
                     23: #   define     VMUNIX  "/vmunix"       /* location of the system namelist */
                     24:     nlist(VMUNIX, nl);
                     25:     if (nl[0].n_type == 0) {
                     26:        fprintf(stderr, "no %s namelist entry for _hz\n", VMUNIX);
                     27:        return 0;
                     28:     }
                     29: #   define     KMEM    "/dev/kmem"     /* location of the system data space */
                     30:     kmem = open(KMEM, 0);
                     31:     if (kmem == -1) {
                     32:        perror("hertz()");
                     33:        fprintf(stderr, "open(\"%s\", 0)", KMEM);
                     34:        return 0;
                     35:     }
                     36:     seeked = lseek(kmem, nl[0].n_value, 0);
                     37:     if (seeked == -1) {
                     38:        fprintf(stderr, "can't lseek(kmem, 0x%x, 0)\n", nl[0].n_value);
                     39:        return 0;
                     40:     }
                     41:     red = read(kmem, &hz, sizeof hz);
                     42:     if (red != sizeof hz) {
                     43:        fprintf(stderr, "read(kmem, 0x%x, %d) returned %d\n",
                     44:                &hz, sizeof hz, red);
                     45:        return 0;
                     46:     }
                     47:     closed = close(kmem);
                     48:     if (closed != 0) {
                     49:        perror("hertz()");
                     50:        fprintf(stderr, "close(\"%s\")", KMEM);
                     51:        return 0;
                     52:     }
                     53:     return hz;
                     54: }

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