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      1 /*	$NetBSD: readhappy.c,v 1.1 2015/05/13 07:07:36 pgoyette Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2015 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * Redistribution and use in source and binary forms, with or without
      8  * modification, are permitted provided that the following conditions
      9  * are met:
     10  * 1. Redistributions of source code must retain the above copyright
     11  *    notice, this list of conditions and the following disclaimer.
     12  * 2. Redistributions in binary form must reproduce the above copyright
     13  *    notice, this list of conditions and the following disclaimer in the
     14  *    documentation and/or other materials provided with the distribution.
     15  *
     16  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     17  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     18  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     19  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     20  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     21  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     22  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     23  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     24  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     25  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     26  * POSSIBILITY OF SUCH DAMAGE.
     27  */
     28 
     29 #include <sys/cdefs.h>
     30 __KERNEL_RCSID(0, "$NetBSD: readhappy.c,v 1.1 2015/05/13 07:07:36 pgoyette Exp $");
     31 
     32 #include <sys/param.h>
     33 #include <sys/conf.h>
     34 #include <sys/device.h>
     35 #include <sys/kernel.h>
     36 #include <sys/module.h>
     37 
     38 /*
     39  * Create a device /dev/happy from which you can read sequential
     40  * happy numbers.
     41  *
     42  * To use this device you need to do:
     43  *     mknod /dev/happy c 210 0
     44  *
     45  * Commentary:
     46  * A happy number is a number defined by the following process: Starting with
     47  * any positive integer, replace the number by the sum of the squares of its
     48  * digits, and repeat the process until the number equals 1 (where it will
     49  * stay), or it loops endlessly in a cycle which does not include 1. Those
     50  * numbers for which this process ends in 1 are happy numbers, while those that
     51  * do not end in 1 are unhappy numbers (or sad numbers).
     52  *
     53  * For more information on happy numbers, and the algorithms, see
     54  *	http://en.wikipedia.org/wiki/Happy_number
     55  *
     56  * The happy number generator is here only to have something that the user
     57  * can read from our device.  Any other arbitrary data generator could
     58  * have been used.  The algorithm is not critical to the implementation
     59  * of the module.
     60  */
     61 
     62 
     63 #define	HAPPY_NUMBER	1
     64 
     65 /* If n is not happy then its sequence ends in the cycle:
     66  * 4, 16, 37, 58, 89, 145, 42, 20, 4, ... */
     67 #define	SAD_NUMBER	4
     68 
     69 /* Calculate the sum of the squares of the digits of n */
     70 static unsigned
     71 dsum(unsigned n)
     72 {
     73 	unsigned sum, x;
     74 	for (sum = 0; n; n /= 10) {
     75 		x = n % 10;
     76 		sum += x * x;
     77 	}
     78 	return sum;
     79 }
     80 
     81 static int
     82 check_happy(unsigned n)
     83 {
     84 	for (;;) {
     85 		unsigned total = dsum(n);
     86 
     87 		if (total == HAPPY_NUMBER)
     88 			return 1;
     89 		if (total == SAD_NUMBER)
     90 			return 0;
     91 
     92 		n = total;
     93 	}
     94 }
     95 
     96 dev_type_open(happy_open);
     97 dev_type_close(happy_close);
     98 dev_type_read(happy_read);
     99 
    100 static struct cdevsw happy_cdevsw = {
    101 	.d_open = happy_open,
    102 	.d_close = happy_close,
    103 	.d_read = happy_read,
    104 	.d_write = nowrite,
    105 	.d_ioctl = noioctl,
    106 	.d_stop = nostop,
    107 	.d_tty = notty,
    108 	.d_poll = nopoll,
    109 	.d_mmap = nommap,
    110 	.d_kqfilter = nokqfilter,
    111 	.d_discard = nodiscard,
    112 	.d_flag = D_OTHER
    113 };
    114 
    115 
    116 struct happy_softc {
    117 	int		refcnt;
    118 	unsigned	last;
    119 };
    120 
    121 static struct happy_softc sc;
    122 
    123 int
    124 happy_open(dev_t self __unused, int flag __unused, int mode __unused,
    125            struct lwp *l __unused)
    126 {
    127 	if (sc.refcnt > 0)
    128 		return EBUSY;
    129 
    130 	sc.last = 0;
    131 	++sc.refcnt;
    132 
    133 	return 0;
    134 }
    135 
    136 int
    137 happy_close(dev_t self __unused, int flag __unused, int mode __unused,
    138             struct lwp *l __unused)
    139 {
    140 	--sc.refcnt;
    141 
    142 	return 0;
    143 }
    144 
    145 int
    146 happy_read(dev_t self __unused, struct uio *uio, int flags __unused)
    147 {
    148 	char line[80];
    149 
    150 	/* Get next happy number */
    151 	while (check_happy(++sc.last) == 0)
    152 		continue;
    153 
    154 	/* Print it into line[] with trailing \n */
    155 	int len = snprintf(line, sizeof(line), "%u\n", sc.last);
    156 
    157 	/* Is there room? */
    158 	if (uio->uio_resid < len) {
    159 		--sc.last; /* Step back */
    160 		return EINVAL;
    161 	}
    162 
    163 	/* Send it to User-Space */
    164 	int e;
    165 	if ((e = uiomove(line, len, uio)))
    166 		return e;
    167 
    168 	return 0;
    169 }
    170 
    171 MODULE(MODULE_CLASS_MISC, happy, NULL);
    172 
    173 static int
    174 happy_modcmd(modcmd_t cmd, void *arg __unused)
    175 {
    176 	/* The major should be verified and changed if needed to avoid
    177 	 * conflicts with other devices. */
    178 	int cmajor = 210, bmajor = -1;
    179 
    180 	switch (cmd) {
    181 	case MODULE_CMD_INIT:
    182 		if (devsw_attach("happy", NULL, &bmajor, &happy_cdevsw,
    183 		                 &cmajor))
    184 			return ENXIO;
    185 		return 0;
    186 	case MODULE_CMD_FINI:
    187 		if (sc.refcnt > 0)
    188 			return EBUSY;
    189 
    190 		devsw_detach(NULL, &happy_cdevsw);
    191 		return 0;
    192 	default:
    193 		return ENOTTY;
    194 	}
    195 }
    196