xref: /netbsd-src/sys/arch/atari/stand/installboot/installboot.c (revision 404fbe5fb94ca1e054339640cabb2801ce52dd30)
1 /*	$NetBSD: installboot.c,v 1.22 2009/01/06 13:35:30 tsutsui Exp $	*/
2 
3 /*
4  * Copyright (c) 1995 Waldi Ravens
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  * 3. All advertising materials mentioning features or use of this software
16  *    must display the following acknowledgement:
17  *        This product includes software developed by Waldi Ravens.
18  * 4. The name of the author may not be used to endorse or promote products
19  *    derived from this software without specific prior written permission
20  *
21  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
22  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
23  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
24  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
25  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
26  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
27  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
28  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
29  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
30  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
31  */
32 
33 #include <sys/types.h>
34 #include <sys/param.h>
35 #include <sys/sysctl.h>
36 #include <sys/ioctl.h>
37 #include <unistd.h>
38 #include <string.h>
39 #include <stdlib.h>
40 #include <stdio.h>
41 #include <paths.h>
42 #include <fcntl.h>
43 #include <errno.h>
44 #include <err.h>
45 #include <limits.h>
46 #include <nlist.h>
47 #include <kvm.h>
48 
49 #define	DKTYPENAMES
50 #define	FSTYPENAMES
51 #include <sys/disklabel.h>
52 #include <machine/ahdilabel.h>
53 
54 #include "installboot.h"
55 
56 static void	usage __P((void));
57 static void	oscheck __P((void));
58 static u_int	abcksum __P((void *));
59 static void	setNVpref __P((void));
60 static void	setIDEpar __P((u_int8_t *, size_t));
61 static void	mkahdiboot __P((struct ahdi_root *, char *,
62 						char *, u_int32_t));
63 static void	mkbootblock __P((struct bootblock *, char *,
64 				char *, struct disklabel *, u_int));
65 static void	install_fd __P((char *, struct disklabel *));
66 static void	install_sd __P((char *, struct disklabel *));
67 static void	install_wd __P((char *, struct disklabel *));
68 
69 static struct bootblock	bootarea;
70 static struct ahdi_root ahdiboot;
71 static const char	mdecpath[] = PATH_MDEC;
72 static const char	stdpath[] = PATH_STD;
73 static const char	milanpath[] = PATH_MILAN;
74 static int		nowrite = 0;
75 static int		verbose = 0;
76 static int		trackpercyl = 0;
77 static int		secpertrack = 0;
78 static int		milan = 0;
79 
80 static void
81 usage ()
82 {
83 	fprintf(stderr,
84 		"usage: installboot [options] device\n"
85 		"where options are:\n"
86 		"\t-N  do not actually write anything on the disk\n"
87 		"\t-m  use Milan boot blocks\n"
88 		"\t-t  number of tracks per cylinder (IDE disk)\n"
89 		"\t-u  number of sectors per track (IDE disk)\n"
90 		"\t-v  verbose mode\n");
91 	exit(EXIT_FAILURE);
92 }
93 
94 int
95 main (argc, argv)
96 	int	argc;
97 	char	*argv[];
98 {
99 	struct disklabel dl;
100 	char		 *dn;
101 	char		 *devchr;
102 	int		 fd, c;
103 
104 	/* check OS bootversion */
105 	oscheck();
106 
107 	/* parse options */
108 	while ((c = getopt(argc, argv, "Nmt:u:v")) != -1) {
109 		switch (c) {
110 		  case 'N':
111 			nowrite = 1;
112 			break;
113 		  case 'm':
114 			milan = 1;
115 			break;
116 		  case 't':
117 			trackpercyl = atoi(optarg);
118 			break;
119 		  case 'u':
120 			secpertrack = atoi(optarg);
121 			break;
122 		  case 'v':
123 			verbose = 1;
124 			break;
125 		  default:
126 			usage();
127 		}
128 	}
129 	argv += optind;
130 	argc -= optind;
131 	if (argc != 1)
132 		usage();
133 
134 	/* get disk label */
135 	dn = alloca(sizeof(_PATH_DEV) + strlen(argv[0]) + 8);
136 	if (!strchr(argv[0], '/')) {
137 		sprintf(dn, "%sr%s%c", _PATH_DEV, argv[0], RAW_PART + 'a');
138 		fd = open(dn, O_RDONLY);
139 		if (fd < 0 && errno == ENOENT) {
140 			sprintf(dn, "%sr%s", _PATH_DEV, argv[0]);
141 			fd = open(dn, O_RDONLY);
142 		}
143 	} else {
144 		sprintf(dn, "%s", argv[0]);
145 		fd = open(dn, O_RDONLY);
146 	}
147 	if (fd < 0)
148 		err(EXIT_FAILURE, "%s", dn);
149 	if (ioctl(fd, DIOCGDINFO, &dl))
150 		err(EXIT_FAILURE, "%s: DIOCGDINFO", dn);
151 	if (close(fd))
152 		err(EXIT_FAILURE, "%s", dn);
153 
154 	/* Eg: in /dev/fd0c, set devchr to point to the 'f' */
155 	devchr = strrchr(dn, '/') + 1;
156 	if (*devchr == 'r')
157 		++devchr;
158 
159 	switch (*devchr) {
160 		case 'f': /* fd */
161 			install_fd(dn, &dl);
162 			break;
163 		case 'w': /* wd */
164 			install_wd(dn, &dl);
165 			setNVpref();
166 			break;
167 		case 's': /* sd */
168 			install_sd(dn, &dl);
169 			setNVpref();
170 			break;
171 		default:
172 			errx(EXIT_FAILURE,
173 			     "%s: '%c': Device type not supported.",
174 			     dn, *devchr);
175 	}
176 
177 	return(EXIT_SUCCESS);
178 }
179 
180 static void
181 oscheck ()
182 {
183 	struct nlist	kbv[] = { { "_bootversion" },
184 				  { NULL } };
185 	kvm_t		*kd_kern;
186 	char		errbuf[_POSIX2_LINE_MAX];
187 	u_short		kvers;
188 	struct stat	sb;
189 
190 	if (stat(_PATH_UNIX, &sb) < 0) {
191 		warnx("Cannot stat %s, no bootversion check done", _PATH_UNIX);
192 		return;
193 	}
194 
195 	kd_kern = kvm_openfiles(NULL, NULL, NULL, O_RDONLY, errbuf);
196 	if (kd_kern == NULL)
197 		errx(EXIT_FAILURE, "kvm_openfiles: %s", errbuf);
198 	if (kvm_nlist(kd_kern, kbv) == -1)
199 		errx(EXIT_FAILURE, "kvm_nlist: %s", kvm_geterr(kd_kern));
200 	if (kbv[0].n_value == 0)
201 		errx(EXIT_FAILURE, "%s not in namelist", kbv[0].n_name);
202 	if (kvm_read(kd_kern, kbv[0].n_value, (char *)&kvers,
203 						sizeof(kvers)) == -1)
204 		errx(EXIT_FAILURE, "kvm_read: %s", kvm_geterr(kd_kern));
205 	kvm_close(kd_kern);
206 	if (kvers != BOOTVERSION)
207 		errx(EXIT_FAILURE, "Kern bootversion: %d, expected: %d",
208 					kvers, BOOTVERSION);
209 }
210 
211 static void
212 install_fd (devnm, label)
213 	char		 *devnm;
214 	struct disklabel *label;
215 {
216 	const char	 *machpath;
217 	char		 *xxboot, *bootxx;
218 	struct partition *rootpart;
219 
220 	if (label->d_secsize != 512)
221 		errx(EXIT_FAILURE,
222 		     "%s: %u: Block size not supported.", devnm,
223 							  label->d_secsize);
224 	if (label->d_ntracks != 2)
225 		errx(EXIT_FAILURE,
226 		     "%s: Single sided floppy not supported.", devnm);
227 
228 	if (milan)
229 		machpath = milanpath;
230 	else
231 		machpath = stdpath;
232 	xxboot = alloca(strlen(mdecpath) + strlen(machpath) + 8);
233 	sprintf(xxboot, "%s%sfdboot", mdecpath, machpath);
234 	bootxx = alloca(strlen(mdecpath) + strlen(machpath) + 8);
235 	sprintf(bootxx, "%s%sbootxx", mdecpath, machpath);
236 
237 	/* first used partition (a, b or c) */		/* XXX */
238 	for (rootpart = label->d_partitions; ; ++rootpart) {
239 		if (rootpart->p_size)
240 			break;
241 	}
242 	if (rootpart != label->d_partitions) {		/* XXX */
243 		*(label->d_partitions) = *rootpart;
244 		memset(rootpart, 0, sizeof(*rootpart));
245 	}
246 	label->d_partitions->p_fstype = FS_BSDFFS;	/* XXX */
247 	label->d_npartitions = 1;
248 	label->d_checksum = 0;
249 	label->d_checksum = dkcksum(label);
250 
251 	trackpercyl = secpertrack = 0;
252 	mkbootblock(&bootarea, xxboot, bootxx, label, 0);
253 
254 	if (!nowrite) {
255 		int	fd;
256 		if ((fd = open(devnm, O_WRONLY)) < 0)
257 			err(EXIT_FAILURE, "%s", devnm);
258 		if (write(fd, &bootarea, sizeof(bootarea)) != sizeof(bootarea))
259 			err(EXIT_FAILURE, "%s", devnm);
260 		if (close(fd))
261 			err(EXIT_FAILURE, "%s", devnm);
262 		if (verbose)
263 			printf("Boot block installed on %s\n", devnm);
264 	}
265 }
266 
267 static void
268 install_sd (devnm, label)
269 	char		 *devnm;
270 	struct disklabel *label;
271 {
272 	const char	 *machpath;
273 	char		 *xxb00t, *xxboot, *bootxx;
274 	struct disklabel rawlabel;
275 	u_int32_t	 bbsec;
276 	u_int		 magic;
277 
278 	if (label->d_partitions[0].p_size == 0)
279 		errx(EXIT_FAILURE, "%s: No root-filesystem.", devnm);
280 	if (label->d_partitions[0].p_fstype != FS_BSDFFS)
281 		errx(EXIT_FAILURE, "%s: %s: Illegal root-filesystem type.",
282 		     devnm, fstypenames[label->d_partitions[0].p_fstype]);
283 
284 	bbsec = readdisklabel(devnm, &rawlabel);
285 	if (bbsec == NO_BOOT_BLOCK)
286 		errx(EXIT_FAILURE, "%s: No NetBSD boot block.", devnm);
287 	if (memcmp(label, &rawlabel, sizeof(*label)))
288 		errx(EXIT_FAILURE, "%s: Invalid NetBSD boot block.", devnm);
289 
290 	if (milan)
291 		machpath = milanpath;
292 	else
293 		machpath = stdpath;
294 	if (bbsec) {
295 		xxb00t = alloca(strlen(mdecpath) + strlen(machpath) + 14);
296 		sprintf(xxb00t, "%s%ssdb00t.ahdi", mdecpath, machpath);
297 		xxboot = alloca(strlen(mdecpath) + strlen(machpath) + 14);
298 		sprintf(xxboot, "%s%sxxboot.ahdi", mdecpath, machpath);
299 		magic = AHDIMAGIC;
300 	} else {
301 		xxb00t = NULL;
302 		xxboot = alloca(strlen(mdecpath) + strlen(machpath) + 8);
303 		sprintf(xxboot, "%s%ssdboot", mdecpath, machpath);
304 		magic = NBDAMAGIC;
305 	}
306 	bootxx = alloca(strlen(mdecpath) + strlen(machpath) + 8);
307 	sprintf(bootxx, "%s%sbootxx", mdecpath, machpath);
308 
309 	trackpercyl = secpertrack = 0;
310 	if (xxb00t)
311 		mkahdiboot(&ahdiboot, xxb00t, devnm, bbsec);
312 	mkbootblock(&bootarea, xxboot, bootxx, label, magic);
313 
314 	if (!nowrite) {
315 		off_t	bbo = (off_t)bbsec * AHDI_BSIZE;
316 		int	fd;
317 
318 		if ((fd = open(devnm, O_WRONLY)) < 0)
319 			err(EXIT_FAILURE, "%s", devnm);
320 		if (lseek(fd, bbo, SEEK_SET) != bbo)
321 			err(EXIT_FAILURE, "%s", devnm);
322 		if (write(fd, &bootarea, sizeof(bootarea)) != sizeof(bootarea))
323 			err(EXIT_FAILURE, "%s", devnm);
324 		if (verbose)
325 			printf("Boot block installed on %s (sector %d)\n", devnm,
326 								    bbsec);
327 		if (xxb00t) {
328 			if (lseek(fd, (off_t)0, SEEK_SET) != 0)
329 				err(EXIT_FAILURE, "%s", devnm);
330 			if (write(fd, &ahdiboot, sizeof(ahdiboot)) != sizeof(ahdiboot))
331 				err(EXIT_FAILURE, "%s", devnm);
332 			if (verbose)
333 				printf("AHDI root  installed on %s (0)\n",
334 								devnm);
335 		}
336 		if (close(fd))
337 			err(EXIT_FAILURE, "%s", devnm);
338 	}
339 }
340 
341 static void
342 install_wd (devnm, label)
343 	char		 *devnm;
344 	struct disklabel *label;
345 {
346 	const char	 *machpath;
347 	char		 *xxb00t, *xxboot, *bootxx;
348 	struct disklabel rawlabel;
349 	u_int32_t	 bbsec;
350 	u_int		 magic;
351 
352 	if (label->d_partitions[0].p_size == 0)
353 		errx(EXIT_FAILURE, "%s: No root-filesystem.", devnm);
354 	if (label->d_partitions[0].p_fstype != FS_BSDFFS)
355 		errx(EXIT_FAILURE, "%s: %s: Illegal root-filesystem type.",
356 		     devnm, fstypenames[label->d_partitions[0].p_fstype]);
357 
358 	bbsec = readdisklabel(devnm, &rawlabel);
359 	if (bbsec == NO_BOOT_BLOCK)
360 		errx(EXIT_FAILURE, "%s: No NetBSD boot block.", devnm);
361 	if (memcmp(label, &rawlabel, sizeof(*label)))
362 		errx(EXIT_FAILURE, "%s: Invalid NetBSD boot block.", devnm);
363 
364 	if (milan)
365 		machpath = milanpath;
366 	else
367 		machpath = stdpath;
368 	if (bbsec) {
369 		xxb00t = alloca(strlen(mdecpath) + strlen(machpath) + 14);
370 		sprintf(xxb00t, "%s%swdb00t.ahdi", mdecpath, machpath);
371 		xxboot = alloca(strlen(mdecpath) + strlen(machpath) + 14);
372 		sprintf(xxboot, "%s%sxxboot.ahdi", mdecpath, machpath);
373 		magic = AHDIMAGIC;
374 	} else {
375 		xxb00t = NULL;
376 		xxboot = alloca(strlen(mdecpath) + strlen(machpath) + 8);
377 		sprintf(xxboot, "%s%swdboot", mdecpath, machpath);
378 		magic = NBDAMAGIC;
379 	}
380 	bootxx = alloca(strlen(mdecpath) + strlen(machpath) + 8);
381 	sprintf(bootxx, "%s%sbootxx", mdecpath, machpath);
382 
383 	if (xxb00t)
384 		mkahdiboot(&ahdiboot, xxb00t, devnm, bbsec);
385 	mkbootblock(&bootarea, xxboot, bootxx, label, magic);
386 
387 	if (!nowrite) {
388 		int	fd;
389 		off_t	bbo;
390 
391 		bbo = (off_t)bbsec * AHDI_BSIZE;
392 		if ((fd = open(devnm, O_WRONLY)) < 0)
393 			err(EXIT_FAILURE, "%s", devnm);
394 		if (lseek(fd, bbo, SEEK_SET) != bbo)
395 			err(EXIT_FAILURE, "%s", devnm);
396 		if (write(fd, &bootarea, sizeof(bootarea)) != sizeof(bootarea))
397 			err(EXIT_FAILURE, "%s", devnm);
398 		if (verbose)
399 			printf("Boot block installed on %s (sector %d)\n", devnm,
400 								    bbsec);
401 		if (xxb00t) {
402 			if (lseek(fd, (off_t)0, SEEK_SET) != 0)
403 				err(EXIT_FAILURE, "%s", devnm);
404 			if (write(fd, &ahdiboot, sizeof(ahdiboot))
405 							!= sizeof(ahdiboot))
406 				err(EXIT_FAILURE, "%s", devnm);
407 			if (verbose)
408 				printf("AHDI root  installed on %s (sector 0)\n",
409 									devnm);
410 		}
411 		if (close(fd))
412 			err(EXIT_FAILURE, "%s", devnm);
413 	}
414 }
415 
416 static void
417 mkahdiboot (newroot, xxb00t, devnm, bbsec)
418 	struct ahdi_root *newroot;
419 	char		 *xxb00t,
420 			 *devnm;
421 	u_int32_t	 bbsec;
422 {
423 	struct ahdi_root tmproot;
424 	struct ahdi_part *pd;
425 	int		 fd;
426 
427 	/* read prototype root-sector */
428 	if ((fd = open(xxb00t, O_RDONLY)) < 0)
429 		err(EXIT_FAILURE, "%s", xxb00t);
430 	if (read(fd, &tmproot, sizeof(tmproot)) != sizeof(tmproot))
431 		err(EXIT_FAILURE, "%s", xxb00t);
432 	if (close(fd))
433 		err(EXIT_FAILURE, "%s", xxb00t);
434 
435 	/* set tracks/cylinder and sectors/track */
436 	setIDEpar(tmproot.ar_fill, sizeof(tmproot.ar_fill));
437 
438 	/* read current root-sector */
439 	if ((fd = open(devnm, O_RDONLY)) < 0)
440 		err(EXIT_FAILURE, "%s", devnm);
441 	if (read(fd, newroot, sizeof(*newroot)) != sizeof(*newroot))
442 		err(EXIT_FAILURE, "%s", devnm);
443 	if (close(fd))
444 		err(EXIT_FAILURE, "%s", devnm);
445 
446 	/* set bootflags */
447 	for (pd = newroot->ar_parts; pd-newroot->ar_parts < AHDI_MAXRPD; ++pd) {
448 		if (pd->ap_st == bbsec) {
449 			pd->ap_flg = 0x21;	/* bootable, pref = NetBSD */
450 			goto gotit;
451 		}
452 	}
453 	errx(EXIT_FAILURE,
454 	     "%s: NetBSD boot block not on primary AHDI partition.", devnm);
455 
456 gotit:	/* copy code from prototype and set new checksum */
457 	memcpy(newroot->ar_fill, tmproot.ar_fill, sizeof(tmproot.ar_fill));
458 	newroot->ar_checksum = 0;
459 	newroot->ar_checksum = 0x1234 - abcksum(newroot);
460 
461 	if (verbose)
462 		printf("AHDI      boot loader: %s\n", xxb00t);
463 }
464 
465 static void
466 mkbootblock (bb, xxb, bxx, label, magic)
467 	struct bootblock *bb;
468 	char		 *xxb,
469 			 *bxx;
470 	u_int		 magic;
471 	struct disklabel *label;
472 {
473 	int		 fd;
474 
475 	memset(bb, 0, sizeof(*bb));
476 
477 	/* set boot block magic */
478 	bb->bb_magic = magic;
479 
480 	/* set disk pack label */
481 	BBSETLABEL(bb, label);
482 
483 	/* set second-stage boot loader */
484 	if ((fd = open(bxx, O_RDONLY)) < 0)
485 		err(EXIT_FAILURE, "%s", bxx);
486 	if (read(fd, bb->bb_bootxx, sizeof(bb->bb_bootxx))
487 					!= sizeof(bb->bb_bootxx))
488 		err(EXIT_FAILURE, "%s", bxx);
489 	if (close(fd))
490 		err(EXIT_FAILURE, "%s", bxx);
491 
492 	/* set first-stage bootloader */
493 	if ((fd = open(xxb, O_RDONLY)) < 0)
494 		err(EXIT_FAILURE, "%s", xxb);
495 	if (read(fd, bb->bb_xxboot, sizeof(bb->bb_xxboot))
496 					!= sizeof(bb->bb_xxboot))
497 		err(EXIT_FAILURE, "%s", xxb);
498 	if (close(fd))
499 		err(EXIT_FAILURE, "%s", xxb);
500 
501 	/* set tracks/cylinder and sectors/track */
502 	setIDEpar(bb->bb_xxboot, sizeof(bb->bb_xxboot));
503 
504 	/* set AHDI checksum */
505 	*((u_int16_t *)bb->bb_xxboot + 255) = 0;
506 	*((u_int16_t *)bb->bb_xxboot + 255) = 0x1234 - abcksum(bb->bb_xxboot);
507 
508 	if (verbose) {
509 		printf("Primary   boot loader: %s\n", xxb);
510 		printf("Secondary boot loader: %s\n", bxx);
511 	}
512 }
513 
514 static void
515 setIDEpar (start, size)
516 	u_int8_t	*start;
517 	size_t		size;
518 {
519 	static const u_int8_t	mark[] = { 'N', 'e', 't', 'B', 'S', 'D' };
520 
521 	if ((u_int)trackpercyl > 255)
522 		errx(EXIT_FAILURE,
523 		     "%d: Illegal tracks/cylinder value (1..255)", trackpercyl);
524 	if ((u_int)secpertrack > 255)
525 		errx(EXIT_FAILURE,
526 		     "%d: Illegal sectors/track value (1..255)", secpertrack);
527 
528 	if (trackpercyl || secpertrack) {
529 		u_int8_t *p;
530 
531 		if (!trackpercyl)
532 			errx(EXIT_FAILURE, "Need tracks/cylinder too.");
533 		if (!secpertrack)
534 			errx(EXIT_FAILURE, "Need sectors/track too.");
535 
536 		start += 2;
537 		size  -= sizeof(mark) + 2;
538 		for (p = start + size; p >= start; --p) {
539 			if (*p != *mark)
540 				continue;
541 			if (!memcmp(p, mark, sizeof(mark)))
542 				break;
543 		}
544 		if (p < start)
545 			errx(EXIT_FAILURE,
546 			     "Malformatted xxboot prototype.");
547 
548 		*--p = secpertrack;
549 		*--p = trackpercyl;
550 
551 		if (verbose) {
552 			printf("sectors/track  : %d\n", secpertrack);
553 			printf("tracks/cylinder: %d\n", trackpercyl);
554 		}
555 	}
556 }
557 
558 static void
559 setNVpref ()
560 {
561 	static const u_char	bootpref = BOOTPREF_NETBSD;
562 	static const char	nvrdev[] = PATH_NVRAM;
563 
564 	if (!nowrite) {
565 		int	fd;
566 
567 		if ((fd = open(nvrdev, O_RDWR)) < 0)
568 			err(EXIT_FAILURE, "%s", nvrdev);
569 		if (lseek(fd, (off_t)1, SEEK_SET) != 1)
570 			err(EXIT_FAILURE, "%s", nvrdev);
571 		if (write(fd, &bootpref, (size_t)1) != 1)
572 			err(EXIT_FAILURE, "%s", nvrdev);
573 		if (close(fd))
574 			err(EXIT_FAILURE, "%s", nvrdev);
575 		if (verbose)
576 			printf("Boot preference set to NetBSD.\n");
577 	}
578 }
579 
580 static u_int
581 abcksum (bs)
582 	void	*bs;
583 {
584 	u_int16_t sum  = 0,
585 		  *st  = (u_int16_t *)bs,
586 		  *end = (u_int16_t *)bs + 256;
587 
588 	while (st < end)
589 		sum += *st++;
590 	return(sum);
591 }
592