xref: /netbsd-src/sbin/dump/traverse.c (revision 2a399c6883d870daece976daec6ffa7bb7f934ce)
1 /*	$NetBSD: traverse.c,v 1.19 1997/09/16 06:41:23 lukem Exp $	*/
2 
3 /*-
4  * Copyright (c) 1980, 1988, 1991, 1993
5  *	The Regents of the University of California.  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 the University of
18  *	California, Berkeley and its contributors.
19  * 4. Neither the name of the University nor the names of its contributors
20  *    may be used to endorse or promote products derived from this software
21  *    without specific prior written permission.
22  *
23  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
24  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
25  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
26  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
27  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
28  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
29  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
30  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
31  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
32  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33  * SUCH DAMAGE.
34  */
35 
36 #include <sys/cdefs.h>
37 #ifndef lint
38 #if 0
39 static char sccsid[] = "@(#)traverse.c	8.7 (Berkeley) 6/15/95";
40 #else
41 __RCSID("$NetBSD: traverse.c,v 1.19 1997/09/16 06:41:23 lukem Exp $");
42 #endif
43 #endif /* not lint */
44 
45 #include <sys/param.h>
46 #include <sys/time.h>
47 #include <sys/stat.h>
48 #ifdef sunos
49 #include <sys/vnode.h>
50 
51 #include <ufs/fs.h>
52 #include <ufs/fsdir.h>
53 #include <ufs/inode.h>
54 #else
55 #include <ufs/ufs/dir.h>
56 #include <ufs/ufs/dinode.h>
57 #include <ufs/ffs/fs.h>
58 #endif
59 
60 #include <protocols/dumprestore.h>
61 
62 #include <ctype.h>
63 #include <errno.h>
64 #include <fts.h>
65 #include <stdio.h>
66 #ifdef __STDC__
67 #include <string.h>
68 #include <unistd.h>
69 #endif
70 
71 #include "dump.h"
72 
73 #define	HASDUMPEDFILE	0x1
74 #define	HASSUBDIRS	0x2
75 
76 #ifdef	FS_44INODEFMT
77 typedef	quad_t fsizeT;
78 #else
79 typedef	int32_t fsizeT;
80 #endif
81 
82 static	int dirindir __P((ino_t ino, daddr_t blkno, int level, long *size));
83 static	void dmpindir __P((ino_t ino, daddr_t blk, int level, fsizeT *size));
84 static	int searchdir __P((ino_t ino, daddr_t blkno, long size, long filesize));
85 
86 /*
87  * This is an estimation of the number of TP_BSIZE blocks in the file.
88  * It estimates the number of blocks in files with holes by assuming
89  * that all of the blocks accounted for by di_blocks are data blocks
90  * (when some of the blocks are usually used for indirect pointers);
91  * hence the estimate may be high.
92  */
93 long
94 blockest(dp)
95 	struct dinode *dp;
96 {
97 	long blkest, sizeest;
98 
99 	/*
100 	 * dp->di_size is the size of the file in bytes.
101 	 * dp->di_blocks stores the number of sectors actually in the file.
102 	 * If there are more sectors than the size would indicate, this just
103 	 *	means that there are indirect blocks in the file or unused
104 	 *	sectors in the last file block; we can safely ignore these
105 	 *	(blkest = sizeest below).
106 	 * If the file is bigger than the number of sectors would indicate,
107 	 *	then the file has holes in it.	In this case we must use the
108 	 *	block count to estimate the number of data blocks used, but
109 	 *	we use the actual size for estimating the number of indirect
110 	 *	dump blocks (sizeest vs. blkest in the indirect block
111 	 *	calculation).
112 	 */
113 	blkest = howmany(dbtob(dp->di_blocks), TP_BSIZE);
114 	sizeest = howmany(dp->di_size, TP_BSIZE);
115 	if (blkest > sizeest)
116 		blkest = sizeest;
117 	if (dp->di_size > sblock->fs_bsize * NDADDR) {
118 		/* calculate the number of indirect blocks on the dump tape */
119 		blkest +=
120 			howmany(sizeest - NDADDR * sblock->fs_bsize / TP_BSIZE,
121 			TP_NINDIR);
122 	}
123 	return (blkest + 1);
124 }
125 
126 /* Auxiliary macro to pick up files changed since previous dump. */
127 #define	CHANGEDSINCE(dp, t) \
128 	((dp)->di_mtime >= (t) || (dp)->di_ctime >= (t))
129 
130 /* The WANTTODUMP macro decides whether a file should be dumped. */
131 #ifdef UF_NODUMP
132 #define	WANTTODUMP(dp) \
133 	(CHANGEDSINCE(dp, spcl.c_ddate) && \
134 	 (nonodump || ((dp)->di_flags & UF_NODUMP) != UF_NODUMP))
135 #else
136 #define	WANTTODUMP(dp) CHANGEDSINCE(dp, spcl.c_ddate)
137 #endif
138 
139 /*
140  * Determine if given inode should be dumped
141  */
142 void
143 mapfileino(ino, tapesize, dirskipped)
144 	ino_t ino;
145 	long *tapesize;
146 	int *dirskipped;
147 {
148 	int mode;
149 	struct dinode *dp;
150 
151 	dp = getino(ino);
152 	if ((mode = (dp->di_mode & IFMT)) == 0)
153 		return;
154 	SETINO(ino, usedinomap);
155 	if (mode == IFDIR)
156 		SETINO(ino, dumpdirmap);
157 	if (WANTTODUMP(dp)) {
158 		SETINO(ino, dumpinomap);
159 		if (mode != IFREG && mode != IFDIR && mode != IFLNK)
160 			*tapesize += 1;
161 		else
162 			*tapesize += blockest(dp);
163 		return;
164 	}
165 	if (mode == IFDIR)
166 		*dirskipped = 1;
167 }
168 
169 /*
170  * Dump pass 1.
171  *
172  * Walk the inode list for a filesystem to find all allocated inodes
173  * that have been modified since the previous dump time. Also, find all
174  * the directories in the filesystem.
175  */
176 int
177 mapfiles(maxino, tapesize, disk, dirv)
178 	ino_t maxino;
179 	long *tapesize;
180 	char *disk;
181 	char * const *dirv;
182 {
183 	int anydirskipped = 0;
184 
185 	if (dirv != NULL) {
186 		char	 curdir[MAXPATHLEN];
187 		FTS	*dirh;
188 		FTSENT	*entry;
189 		int	 d;
190 
191 		if (getcwd(curdir, sizeof(curdir)) == NULL) {
192 			msg("Can't determine cwd: %s\n", strerror(errno));
193 			dumpabort(0);
194 		}
195 		if ((dirh = fts_open(dirv, FTS_PHYSICAL|FTS_SEEDOT|FTS_XDEV,
196 		    		    NULL)) == NULL) {
197 			msg("fts_open failed: %s\n", strerror(errno));
198 			dumpabort(0);
199 		}
200 		while ((entry = fts_read(dirh)) != NULL) {
201 			switch (entry->fts_info) {
202 			case FTS_DNR:		/* an error */
203 			case FTS_ERR:
204 			case FTS_NS:
205 				msg("Can't fts_read %s: %s\n", entry->fts_path,
206 				    strerror(errno));
207 			case FTS_DP:		/* already seen dir */
208 				continue;
209 			}
210 			mapfileino(entry->fts_statp->st_ino, tapesize,
211 			    &anydirskipped);
212 		}
213 		(void)fts_close(dirh);
214 
215 		/*
216 		 * Add any parent directories
217 		 */
218 		for (d = 0 ; dirv[d] != NULL ; d++) {
219 			char path[MAXPATHLEN];
220 
221 			if (dirv[d][0] != '/')
222 				(void)snprintf(path, sizeof(path), "%s/%s",
223 				    curdir, dirv[d]);
224 			else
225 				(void)snprintf(path, sizeof(path), "%s",
226 				    dirv[d]);
227 			while (strcmp(path, disk) != 0) {
228 				char *p;
229 				struct stat sb;
230 
231 				if (*path == '\0')
232 					break;
233 				if ((p = strrchr(path, '/')) == NULL)
234 					break;
235 				if (p == path)
236 					break;
237 				*p = '\0';
238 				if (stat(path, &sb) == -1) {
239 					msg("Can't stat %s: %s\n", path,
240 					    strerror(errno));
241 					break;
242 				}
243 				mapfileino(sb.st_ino, tapesize, &anydirskipped);
244 			}
245 		}
246 
247 		/*
248 		 * Ensure that the root inode actually appears in the
249 		 * file list for a subdir
250 		 */
251 		mapfileino(ROOTINO, tapesize, &anydirskipped);
252 	} else {
253 		ino_t ino;
254 
255 		for (ino = ROOTINO; ino < maxino; ino++) {
256 			mapfileino(ino, tapesize, &anydirskipped);
257 		}
258 	}
259 	/*
260 	 * Restore gets very upset if the root is not dumped,
261 	 * so ensure that it always is dumped.
262 	 */
263 	SETINO(ROOTINO, dumpinomap);
264 	return (anydirskipped);
265 }
266 
267 /*
268  * Dump pass 2.
269  *
270  * Scan each directory on the filesystem to see if it has any modified
271  * files in it. If it does, and has not already been added to the dump
272  * list (because it was itself modified), then add it. If a directory
273  * has not been modified itself, contains no modified files and has no
274  * subdirectories, then it can be deleted from the dump list and from
275  * the list of directories. By deleting it from the list of directories,
276  * its parent may now qualify for the same treatment on this or a later
277  * pass using this algorithm.
278  */
279 int
280 mapdirs(maxino, tapesize)
281 	ino_t maxino;
282 	long *tapesize;
283 {
284 	struct	dinode *dp;
285 	int i, isdir;
286 	char *map;
287 	ino_t ino;
288 	long filesize;
289 	int ret, change = 0;
290 
291 	isdir = 0;		/* XXX just to get gcc to shut up */
292 	for (map = dumpdirmap, ino = 1; ino < maxino; ino++) {
293 		if (((ino - 1) % NBBY) == 0)	/* map is offset by 1 */
294 			isdir = *map++;
295 		else
296 			isdir >>= 1;
297 		if ((isdir & 1) == 0 || TSTINO(ino, dumpinomap))
298 			continue;
299 		dp = getino(ino);
300 		filesize = dp->di_size;
301 		for (ret = 0, i = 0; filesize > 0 && i < NDADDR; i++) {
302 			if (dp->di_db[i] != 0)
303 				ret |= searchdir(ino, dp->di_db[i],
304 					(long)dblksize(sblock, dp, i),
305 					filesize);
306 			if (ret & HASDUMPEDFILE)
307 				filesize = 0;
308 			else
309 				filesize -= sblock->fs_bsize;
310 		}
311 		for (i = 0; filesize > 0 && i < NIADDR; i++) {
312 			if (dp->di_ib[i] == 0)
313 				continue;
314 			ret |= dirindir(ino, dp->di_ib[i], i, &filesize);
315 		}
316 		if (ret & HASDUMPEDFILE) {
317 			SETINO(ino, dumpinomap);
318 			*tapesize += blockest(dp);
319 			change = 1;
320 			continue;
321 		}
322 		if ((ret & HASSUBDIRS) == 0) {
323 			if (!TSTINO(ino, dumpinomap)) {
324 				CLRINO(ino, dumpdirmap);
325 				change = 1;
326 			}
327 		}
328 	}
329 	return (change);
330 }
331 
332 /*
333  * Read indirect blocks, and pass the data blocks to be searched
334  * as directories. Quit as soon as any entry is found that will
335  * require the directory to be dumped.
336  */
337 static int
338 dirindir(ino, blkno, ind_level, filesize)
339 	ino_t ino;
340 	daddr_t blkno;
341 	int ind_level;
342 	long *filesize;
343 {
344 	int ret = 0;
345 	int i;
346 	daddr_t	idblk[MAXNINDIR];
347 
348 	bread(fsbtodb(sblock, blkno), (char *)idblk, (int)sblock->fs_bsize);
349 	if (ind_level <= 0) {
350 		for (i = 0; *filesize > 0 && i < NINDIR(sblock); i++) {
351 			blkno = idblk[i];
352 			if (blkno != 0)
353 				ret |= searchdir(ino, blkno, sblock->fs_bsize,
354 					*filesize);
355 			if (ret & HASDUMPEDFILE)
356 				*filesize = 0;
357 			else
358 				*filesize -= sblock->fs_bsize;
359 		}
360 		return (ret);
361 	}
362 	ind_level--;
363 	for (i = 0; *filesize > 0 && i < NINDIR(sblock); i++) {
364 		blkno = idblk[i];
365 		if (blkno != 0)
366 			ret |= dirindir(ino, blkno, ind_level, filesize);
367 	}
368 	return (ret);
369 }
370 
371 /*
372  * Scan a disk block containing directory information looking to see if
373  * any of the entries are on the dump list and to see if the directory
374  * contains any subdirectories.
375  */
376 static int
377 searchdir(ino, blkno, size, filesize)
378 	ino_t ino;
379 	daddr_t blkno;
380 	long size;
381 	long filesize;
382 {
383 	struct direct *dp;
384 	long loc, ret = 0;
385 	char dblk[MAXBSIZE];
386 
387 	bread(fsbtodb(sblock, blkno), dblk, (int)size);
388 	if (filesize < size)
389 		size = filesize;
390 	for (loc = 0; loc < size; ) {
391 		dp = (struct direct *)(dblk + loc);
392 		if (dp->d_reclen == 0) {
393 			msg("corrupted directory, inumber %d\n", ino);
394 			break;
395 		}
396 		loc += dp->d_reclen;
397 		if (dp->d_ino == 0)
398 			continue;
399 		if (dp->d_name[0] == '.') {
400 			if (dp->d_name[1] == '\0')
401 				continue;
402 			if (dp->d_name[1] == '.' && dp->d_name[2] == '\0')
403 				continue;
404 		}
405 		if (TSTINO(dp->d_ino, dumpinomap)) {
406 			ret |= HASDUMPEDFILE;
407 			if (ret & HASSUBDIRS)
408 				break;
409 		}
410 		if (TSTINO(dp->d_ino, dumpdirmap)) {
411 			ret |= HASSUBDIRS;
412 			if (ret & HASDUMPEDFILE)
413 				break;
414 		}
415 	}
416 	return (ret);
417 }
418 
419 /*
420  * Dump passes 3 and 4.
421  *
422  * Dump the contents of an inode to tape.
423  */
424 void
425 dumpino(dp, ino)
426 	struct dinode *dp;
427 	ino_t ino;
428 {
429 	int ind_level, cnt;
430 	fsizeT size;
431 	char buf[TP_BSIZE];
432 
433 	if (newtape) {
434 		newtape = 0;
435 		dumpmap(dumpinomap, TS_BITS, ino);
436 	}
437 	CLRINO(ino, dumpinomap);
438 	spcl.c_dinode = *dp;
439 	spcl.c_type = TS_INODE;
440 	spcl.c_count = 0;
441 	switch (dp->di_mode & IFMT) {
442 
443 	case 0:
444 		/*
445 		 * Freed inode.
446 		 */
447 		return;
448 
449 	case IFLNK:
450 		/*
451 		 * Check for short symbolic link.
452 		 */
453 		if (dp->di_size > 0 &&
454 #ifdef FS_44INODEFMT
455 		    (dp->di_size < sblock->fs_maxsymlinklen ||
456 		     (sblock->fs_maxsymlinklen == 0 && dp->di_blocks == 0))) {
457 #else
458 		    dp->di_blocks == 0) {
459 #endif
460 			spcl.c_addr[0] = 1;
461 			spcl.c_count = 1;
462 			writeheader(ino);
463 			memmove(buf, dp->di_shortlink, (u_long)dp->di_size);
464 			buf[dp->di_size] = '\0';
465 			writerec(buf, 0);
466 			return;
467 		}
468 		/* fall through */
469 
470 	case IFDIR:
471 	case IFREG:
472 		if (dp->di_size > 0)
473 			break;
474 		/* fall through */
475 
476 	case IFIFO:
477 	case IFSOCK:
478 	case IFCHR:
479 	case IFBLK:
480 		writeheader(ino);
481 		return;
482 
483 	default:
484 		msg("Warning: undefined file type 0%o\n", dp->di_mode & IFMT);
485 		return;
486 	}
487 	if (dp->di_size > NDADDR * sblock->fs_bsize)
488 		cnt = NDADDR * sblock->fs_frag;
489 	else
490 		cnt = howmany(dp->di_size, sblock->fs_fsize);
491 	blksout(&dp->di_db[0], cnt, ino);
492 	if ((size = dp->di_size - NDADDR * sblock->fs_bsize) <= 0)
493 		return;
494 	for (ind_level = 0; ind_level < NIADDR; ind_level++) {
495 		dmpindir(ino, dp->di_ib[ind_level], ind_level, &size);
496 		if (size <= 0)
497 			return;
498 	}
499 }
500 
501 /*
502  * Read indirect blocks, and pass the data blocks to be dumped.
503  */
504 static void
505 dmpindir(ino, blk, ind_level, size)
506 	ino_t ino;
507 	daddr_t blk;
508 	int ind_level;
509 	fsizeT *size;
510 {
511 	int i, cnt;
512 	daddr_t idblk[MAXNINDIR];
513 
514 	if (blk != 0)
515 		bread(fsbtodb(sblock, blk), (char *)idblk, (int) sblock->fs_bsize);
516 	else
517 		memset(idblk, 0, (int)sblock->fs_bsize);
518 	if (ind_level <= 0) {
519 		if (*size < NINDIR(sblock) * sblock->fs_bsize)
520 			cnt = howmany(*size, sblock->fs_fsize);
521 		else
522 			cnt = NINDIR(sblock) * sblock->fs_frag;
523 		*size -= NINDIR(sblock) * sblock->fs_bsize;
524 		blksout(&idblk[0], cnt, ino);
525 		return;
526 	}
527 	ind_level--;
528 	for (i = 0; i < NINDIR(sblock); i++) {
529 		dmpindir(ino, idblk[i], ind_level, size);
530 		if (*size <= 0)
531 			return;
532 	}
533 }
534 
535 /*
536  * Collect up the data into tape record sized buffers and output them.
537  */
538 void
539 blksout(blkp, frags, ino)
540 	daddr_t *blkp;
541 	int frags;
542 	ino_t ino;
543 {
544 	daddr_t *bp;
545 	int i, j, count, blks, tbperdb;
546 
547 	blks = howmany(frags * sblock->fs_fsize, TP_BSIZE);
548 	tbperdb = sblock->fs_bsize >> tp_bshift;
549 	for (i = 0; i < blks; i += TP_NINDIR) {
550 		if (i + TP_NINDIR > blks)
551 			count = blks;
552 		else
553 			count = i + TP_NINDIR;
554 		for (j = i; j < count; j++)
555 			if (blkp[j / tbperdb] != 0)
556 				spcl.c_addr[j - i] = 1;
557 			else
558 				spcl.c_addr[j - i] = 0;
559 		spcl.c_count = count - i;
560 		writeheader(ino);
561 		bp = &blkp[i / tbperdb];
562 		for (j = i; j < count; j += tbperdb, bp++)
563 			if (*bp != 0)
564 				if (j + tbperdb <= count)
565 					dumpblock(*bp, (int)sblock->fs_bsize);
566 				else
567 					dumpblock(*bp, (count - j) * TP_BSIZE);
568 		spcl.c_type = TS_ADDR;
569 	}
570 }
571 
572 /*
573  * Dump a map to the tape.
574  */
575 void
576 dumpmap(map, type, ino)
577 	char *map;
578 	int type;
579 	ino_t ino;
580 {
581 	int i;
582 	char *cp;
583 
584 	spcl.c_type = type;
585 	spcl.c_count = howmany(mapsize * sizeof(char), TP_BSIZE);
586 	writeheader(ino);
587 	for (i = 0, cp = map; i < spcl.c_count; i++, cp += TP_BSIZE)
588 		writerec(cp, 0);
589 }
590 
591 /*
592  * Write a header record to the dump tape.
593  */
594 void
595 writeheader(ino)
596 	ino_t ino;
597 {
598 	int32_t sum, cnt, *lp;
599 
600 	spcl.c_inumber = ino;
601 	spcl.c_magic = NFS_MAGIC;
602 	spcl.c_checksum = 0;
603 	lp = (int32_t *)&spcl;
604 	sum = 0;
605 	cnt = sizeof(union u_spcl) / (4 * sizeof(int32_t));
606 	while (--cnt >= 0) {
607 		sum += *lp++;
608 		sum += *lp++;
609 		sum += *lp++;
610 		sum += *lp++;
611 	}
612 	spcl.c_checksum = CHECKSUM - sum;
613 	writerec((char *)&spcl, 1);
614 }
615 
616 struct dinode *
617 getino(inum)
618 	ino_t inum;
619 {
620 	static daddr_t minino, maxino;
621 	static struct dinode inoblock[MAXINOPB];
622 
623 	curino = inum;
624 	if (inum >= minino && inum < maxino)
625 		return (&inoblock[inum - minino]);
626 	bread(fsbtodb(sblock, ino_to_fsba(sblock, inum)), (char *)inoblock,
627 	    (int)sblock->fs_bsize);
628 	minino = inum - (inum % INOPB(sblock));
629 	maxino = minino + INOPB(sblock);
630 	return (&inoblock[inum - minino]);
631 }
632 
633 /*
634  * Read a chunk of data from the disk.
635  * Try to recover from hard errors by reading in sector sized pieces.
636  * Error recovery is attempted at most BREADEMAX times before seeking
637  * consent from the operator to continue.
638  */
639 int	breaderrors = 0;
640 #define	BREADEMAX 32
641 
642 void
643 bread(blkno, buf, size)
644 	daddr_t blkno;
645 	char *buf;
646 	int size;
647 {
648 	int cnt, i;
649 	extern int errno;
650 
651 loop:
652 	if (lseek(diskfd, ((off_t)blkno << dev_bshift), 0) < 0)
653 		msg("bread: lseek fails\n");
654 	if ((cnt = read(diskfd, buf, size)) == size)
655 		return;
656 	if (blkno + (size / dev_bsize) > fsbtodb(sblock, sblock->fs_size)) {
657 		/*
658 		 * Trying to read the final fragment.
659 		 *
660 		 * NB - dump only works in TP_BSIZE blocks, hence
661 		 * rounds `dev_bsize' fragments up to TP_BSIZE pieces.
662 		 * It should be smarter about not actually trying to
663 		 * read more than it can get, but for the time being
664 		 * we punt and scale back the read only when it gets
665 		 * us into trouble. (mkm 9/25/83)
666 		 */
667 		size -= dev_bsize;
668 		goto loop;
669 	}
670 	if (cnt == -1)
671 		msg("read error from %s: %s: [block %d]: count=%d\n",
672 			disk, strerror(errno), blkno, size);
673 	else
674 		msg("short read error from %s: [block %d]: count=%d, got=%d\n",
675 			disk, blkno, size, cnt);
676 	if (++breaderrors > BREADEMAX) {
677 		msg("More than %d block read errors from %d\n",
678 			BREADEMAX, disk);
679 		broadcast("DUMP IS AILING!\n");
680 		msg("This is an unrecoverable error.\n");
681 		if (!query("Do you want to attempt to continue?")){
682 			dumpabort(0);
683 			/*NOTREACHED*/
684 		} else
685 			breaderrors = 0;
686 	}
687 	/*
688 	 * Zero buffer, then try to read each sector of buffer separately.
689 	 */
690 	memset(buf, 0, size);
691 	for (i = 0; i < size; i += dev_bsize, buf += dev_bsize, blkno++) {
692 		if (lseek(diskfd, ((off_t)blkno << dev_bshift), 0) < 0)
693 			msg("bread: lseek2 fails!\n");
694 		if ((cnt = read(diskfd, buf, (int)dev_bsize)) == dev_bsize)
695 			continue;
696 		if (cnt == -1) {
697 			msg("read error from %s: %s: [sector %d]: count=%d\n",
698 				disk, strerror(errno), blkno, dev_bsize);
699 			continue;
700 		}
701 		msg("short read error from %s: [sector %d]: count=%d, got=%d\n",
702 			disk, blkno, dev_bsize, cnt);
703 	}
704 }
705