text: /*	$OpenBSD: disksubr.c,v 1.39 2004/03/17 14:16:00 miod Exp $	*/
  /*	$NetBSD: disksubr.c,v 1.21 1996/05/03 19:42:03 christos Exp $	*/
  
  /*
   * Copyright (c) 1997 Niklas Hallqvist
   * Copyright (c) 1996 Theo de Raadt
   * Copyright (c) 1982, 1986, 1988 Regents of the University of California.
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. Neither the name of the University nor the names of its contributors
   *    may be used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   *
   *	@(#)ufs_disksubr.c	7.16 (Berkeley) 5/4/91
   */
  
  /*
   * This disksubr.c module started to take its present form on OpenBSD/alpha
   * but it was always thought it should be made completely MI and not need to
   * be in that alpha-specific tree at all.
   *
   * XXX The DOS partitioning code is not endian-independent, only native
   * endian DOS partition tables can be parsed yet.
   *
   * XXX Amiga RDB partitioning is not understood yet.
   */
  
  #include <sys/param.h>
  #include <sys/systm.h>
  #include <sys/buf.h>
  #include <sys/device.h>
  #include <sys/disklabel.h>
  #include <sys/syslog.h>
  #include <sys/disk.h>
  
  /* The native defaults... */
  #if defined(alpha) && !defined(DISKLABEL_ALPHA)
  #define DISKLABEL_ALPHA
  #elif (defined(i386) || defined(arc)) && !defined(DISKLABEL_I386)
  #define DISKLABEL_I386
  #elif defined(amiga) && !defined(DISKLABEL_AMIGA)
  #define DISKLABEL_AMIGA
  #endif
  
  #if defined(DISKLABEL_I386) || defined(DISKLABEL_ALPHA) || defined(DISKLABEL_AMIGA) || defined(DISKLABEL_ALL)
  void	swapdisklabel(struct disklabel *d);
  char   *readbsdlabel(struct buf *, void (*)(struct buf *), int, int,
      int, int, struct disklabel *, int);
  #endif
  #if defined(DISKLABEL_I386) || defined(DISKLABEL_ALL)
  char   *readdoslabel(struct buf *, void (*)(struct buf *),
      struct disklabel *, struct cpu_disklabel *, int *, int *, int);
  #endif
  #if defined(DISKLABEL_AMIGA) || defined(DISKLABEL_ALL)
  char   *readamigalabel(struct buf *, void (*)(struct buf *),
      struct disklabel *, struct cpu_disklabel *, int);
  #endif
  
  static enum disklabel_tag probe_order[] = { LABELPROBES, -1 };
  
  void
  dk_establish(dk, dev)
  	struct disk *dk;
  	struct device *dev;
  {
  }
  
  #if defined(DISKLABEL_I386) || defined(DISKLABEL_ALPHA) || defined(DISKLABEL_AMIGA) || defined(DISKLABEL_ALL)
  
  /*
   * Byteswap all the fields that might be swapped.
   */
  void
  swapdisklabel(dlp)
  	struct disklabel *dlp;
  {
  	int i;
  	struct partition *pp;
  
  	swap32(dlp->d_magic);
  	swap16(dlp->d_type);
  	swap16(dlp->d_subtype);
  	swap32(dlp->d_secsize);
  	swap32(dlp->d_nsectors);
  	swap32(dlp->d_ntracks);
  	swap32(dlp->d_ncylinders);
  	swap32(dlp->d_secpercyl);
  	swap32(dlp->d_secperunit);
  	swap16(dlp->d_sparespertrack);
  	swap16(dlp->d_sparespercyl);
  	swap32(dlp->d_acylinders);
  	swap16(dlp->d_rpm);
  	swap16(dlp->d_interleave);
  	swap16(dlp->d_trackskew);
  	swap16(dlp->d_cylskew);
  	swap32(dlp->d_headswitch);
  	swap32(dlp->d_trkseek);
  	swap32(dlp->d_flags);
  	for (i = 0; i < NDDATA; i++)
  		swap32(dlp->d_drivedata[i]);
  	for (i = 0; i < NSPARE; i++)
  		swap32(dlp->d_spare[i]);
  	swap32(dlp->d_magic2);
  	swap16(dlp->d_checksum);
  	swap16(dlp->d_npartitions);
  	swap32(dlp->d_bbsize);
  	swap32(dlp->d_sbsize);
  	for (i = 0; i < MAXPARTITIONS; i++) {
  		pp = &dlp->d_partitions[i];
  		swap32(pp->p_size);
  		swap32(pp->p_offset);
  		swap32(pp->p_fsize);
  		swap16(pp->p_cpg);
  	}
  }
  
  /*
   * Try to read a standard BSD disklabel at a certain sector.
   */
  char *
  readbsdlabel(bp, strat, cyl, sec, off, endian, lp, spoofonly)
  	struct buf *bp;
  	void (*strat)(struct buf *);
  	int cyl, sec, off, endian;
  	struct disklabel *lp;
  	int spoofonly;
  {
  	struct disklabel *dlp;
  	char *msg = NULL;
  	u_int16_t cksum;
  	u_int32_t magic;
  
  	if (endian != LITTLE_ENDIAN && endian != BIG_ENDIAN)
  		panic("readbsdlabel: unsupported byteorder %d", endian);
  
  	/* don't read the on-disk label if we are in spoofed-only mode */
  	if (spoofonly)
  		return (NULL);
  
  	bp->b_blkno = sec;
  	bp->b_cylinder = cyl;
  	bp->b_bcount = lp->d_secsize;
  	bp->b_flags = B_BUSY | B_READ;
  	(*strat)(bp);
  
  	/* if successful, locate disk label within block and validate */
  	if (biowait(bp)) {
  		/* XXX we return the faked label built so far */
  		msg = "disk label I/O error";
  		return (msg);
  	}
  
  	magic = endian == BIG_ENDIAN ? htobe32(DISKMAGIC) : htole32(DISKMAGIC);
  
  	/*
  	 * If off is negative, search until the end of the sector for
  	 * the label, otherwise, just look at the specific location
  	 * we're given.
  	 */
  	dlp = (struct disklabel *)(bp->b_data + (off >= 0 ? off : 0));
  	do {
  		if (dlp->d_magic != magic || dlp->d_magic2 != magic) {
  			if (msg == NULL)
  				msg = "no disk label";
  		} else {
  			cksum = dkcksum(dlp);
  			if (endian != BYTE_ORDER)
  				swapdisklabel(dlp);
  			if (dlp->d_npartitions > MAXPARTITIONS || cksum != 0) {
  				msg = "disk label corrupted";
  				/* swap back if necessary.  */
  				if (off < 0 && endian != BYTE_ORDER)
  					swapdisklabel(dlp);
  			} else {
  				*lp = *dlp;
  				/* Recalc magic on foreign labels */
  				if (endian != BYTE_ORDER) {
  					lp->d_checksum = 0;
  					lp->d_checksum = dkcksum(lp);
  				}
  				msg = NULL;
  				break;
  			}
  		}
  		if (off >= 0)
  			break;
  		dlp = (struct disklabel *)((char *)dlp + sizeof(int32_t));
  	} while (dlp <= (struct disklabel *)(bp->b_data + lp->d_secsize -
  	    sizeof(*dlp)));
  	return (msg);
  }
  #endif
  
  /*
   * Attempt to read a disk label from a device
   * using the indicated strategy routine.
   * The label must be partly set up before this:
   * secpercyl, secsize and anything required for a block i/o read
   * operation in the driver's strategy/start routines
   * must be filled in before calling us.
   *
   * Returns null on success and an error string on failure.
   */
  char *
  readdisklabel(dev, strat, lp, osdep, spoofonly)
  	dev_t dev;
  	void (*strat)(struct buf *);
  	struct disklabel *lp;
  	struct cpu_disklabel *osdep;
  	int spoofonly;
  {
  	struct buf *bp = NULL;
  	char *msg = "no disk label";
  	enum disklabel_tag *tp;
  	int i;
  	struct disklabel minilabel, fallbacklabel;
  
  	/* minimal requirements for archetypal disk label */
  	if (lp->d_secsize < DEV_BSIZE)
  		lp->d_secsize = DEV_BSIZE;
  	if (lp->d_secperunit == 0)
  		lp->d_secperunit = 0x1fffffff;
  	if (lp->d_secpercyl == 0) {
  		msg = "invalid geometry";
  		goto done;
  	}
  	lp->d_npartitions = RAW_PART + 1;
  	for (i = 0; i < RAW_PART; i++) {
  		lp->d_partitions[i].p_size = 0;
  		lp->d_partitions[i].p_offset = 0;
  	}
  	if (lp->d_partitions[i].p_size == 0)
  		lp->d_partitions[i].p_size = 0x1fffffff;
  	lp->d_partitions[i].p_offset = 0;
  	minilabel = fallbacklabel = *lp;
  
  	/* get a buffer and initialize it */
  	bp = geteblk((int)lp->d_secsize);
  	bp->b_dev = dev;
  
  	for (tp = probe_order; msg && *tp != -1; tp++) {
  		switch (*tp) {
  		case DLT_ALPHA:
  #if defined(DISKLABEL_ALPHA) || defined(DISKLABEL_ALL)
  			msg = readbsdlabel(bp, strat, 0, ALPHA_LABELSECTOR,
  			    ALPHA_LABELOFFSET, LITTLE_ENDIAN, lp, spoofonly);
  #endif
  			break;
  
  		case DLT_I386:
  #if defined(DISKLABEL_I386) || defined(DISKLABEL_ALL)
  			msg = readdoslabel(bp, strat, lp, osdep, 0, 0, spoofonly);
  			if (msg)
  				/* Fallback alternative */
  				fallbacklabel = *lp;
  #endif
  			break;
  
  		case DLT_AMIGA:
  #if defined(DISKLABEL_AMIGA) || defined(DISKLABEL_ALL)
  			msg = readamigalabel(bp, strat, lp, osdep, spoofonly);
  #endif
  			break;
  
  		default:
  			panic("unrecognized disklabel tag %d", *tp);
  		}
  		if (msg)
  			*lp = minilabel;
  	}
  
  	/* Record metainformation about the disklabel.  */
  	if (msg == NULL) {
  		osdep->labelsector = bp->b_blkno;
  		osdep->labeltag = *tp;
  	}
  
  #if defined(CD9660)
  	if (msg && iso_disklabelspoof(dev, strat, lp) == 0)
  		msg = NULL;
  #endif
  
  	/* If there was an error, still provide a decent fake one.  */
  	if (msg)
  		*lp = fallbacklabel;
  
  done:
  	if (bp) {
  		bp->b_flags |= B_INVAL;
  		brelse(bp);
  	}
  	return (msg);
  }
  
  #if defined(DISKLABEL_I386) || defined(DISKLABEL_ALL)
  /*
   * If dos partition table requested, attempt to load it and
   * find disklabel inside a DOS partition. Also, if bad block
   * table needed, attempt to extract it as well. Return buffer
   * for use in signalling errors if requested.
   *
   * We would like to check if each MBR has a valid BOOT_MAGIC, but
   * we cannot because it doesn't always exist. So.. we assume the
   * MBR is valid.
   */
  char *
  readdoslabel(bp, strat, lp, osdep, partoffp, cylp, spoofonly)
  	struct buf *bp;
  	void (*strat)(struct buf *);
  	struct disklabel *lp;
  	struct cpu_disklabel *osdep;
  	int *partoffp;
  	int *cylp;
  	int spoofonly;
  {
  	struct dos_partition *dp = osdep->u._i386.dosparts, *dp2;
  	struct dkbad *db, *bdp = &DKBAD(osdep);
  	char *msg = NULL, *cp;
  	int dospartoff, cyl, i, ourpart = -1;
  	dev_t dev;
  
  	if (lp->d_secpercyl == 0) {
  		msg = "invalid label, d_secpercyl == 0";
  		return (msg);
  	}
  	if (lp->d_secsize == 0) {
  		msg = "invalid label, d_secsize == 0";
  		return (msg);
  	}
  
  	/* do dos partitions in the process of getting disklabel? */
  	dospartoff = 0;
  	cyl = I386_LABELSECTOR / lp->d_secpercyl;
  	if (dp) {
  	        daddr_t part_blkno = DOSBBSECTOR;
  		unsigned long extoff = 0;
  		int wander = 1, n = 0, loop = 0;
  
  		/*
  		 * Read dos partition table, follow extended partitions.
  		 * Map the partitions to disklabel entries i-p
  		 */
  		while (wander && n < 8 && loop < 8) {
  		        loop++;
  			wander = 0;
  			if (part_blkno < extoff)
  				part_blkno = extoff;
  
  			/* read boot record */
  			bp->b_blkno = part_blkno;
  			bp->b_bcount = lp->d_secsize;
  			bp->b_flags = B_BUSY | B_READ;
  			bp->b_cylinder = part_blkno / lp->d_secpercyl;
  			(*strat)(bp);
  		     
  			/* if successful, wander through dos partition table */
  			if (biowait(bp)) {
  				msg = "dos partition I/O error";
  				if (partoffp)
  					*partoffp = -1;
  				return (msg);
  			}
  			bcopy(bp->b_data + DOSPARTOFF, dp,
  			    NDOSPART * sizeof(*dp));
  
  			if (ourpart == -1) {
  				/* Search for our MBR partition */
  				for (dp2=dp, i=0;
  				    i < NDOSPART && ourpart == -1; i++, dp2++)
  					if (dp2->dp_size &&
  					    dp2->dp_typ == DOSPTYP_OPENBSD)
  						ourpart = i;
  				for (dp2=dp, i=0;
  				    i < NDOSPART && ourpart == -1; i++, dp2++)
  					if (dp2->dp_size &&
  					    dp2->dp_typ == DOSPTYP_FREEBSD)
  						ourpart = i;
  				for (dp2=dp, i=0;
  				    i < NDOSPART && ourpart == -1; i++, dp2++)
  					if (dp2->dp_size &&
  					    dp2->dp_typ == DOSPTYP_NETBSD)
  						ourpart = i;
  				if (ourpart == -1)
  					goto donot;
  				/*
  				 * This is our MBR partition. need sector
  				 * address for SCSI/IDE, cylinder for
  				 * ESDI/ST506/RLL
  				 */
  				dp2 = &dp[ourpart];
  				dospartoff = dp2->dp_start + part_blkno;
  				cyl = DPCYL(dp2->dp_scyl, dp2->dp_ssect);
  
  				/* XXX build a temporary disklabel */
  				lp->d_partitions[0].p_size = dp2->dp_size;
  				lp->d_partitions[0].p_offset = dp2->dp_start +
  				    part_blkno;
  				if (lp->d_ntracks == 0)
  					lp->d_ntracks = dp2->dp_ehd + 1;
  				if (lp->d_nsectors == 0)
  					lp->d_nsectors = DPSECT(dp2->dp_esect);
  				if (lp->d_secpercyl == 0)
  					lp->d_secpercyl = lp->d_ntracks *
  					    lp->d_nsectors;
  			}
  donot:
  			/*
  			 * In case the disklabel read below fails, we want to
  			 * provide a fake label in i-p.
  			 */
  			for (dp2=dp, i=0; i < NDOSPART && n < 8; i++, dp2++) {
  				struct partition *pp = &lp->d_partitions[8+n];
  
  				if (dp2->dp_typ == DOSPTYP_OPENBSD)
  					continue;
  				if (dp2->dp_size)
  					pp->p_size = dp2->dp_size;
  				if (dp2->dp_start)
  					pp->p_offset =
  					    dp2->dp_start + part_blkno;
  
  				switch (dp2->dp_typ) {
  				case DOSPTYP_UNUSED:
  					for (cp = (char *)dp2;
  					    cp < (char *)(dp2 + 1); cp++)
  						if (*cp)
  							break;
  					/*
  					 * Was it all zeroes?  If so, it is
  					 * an unused entry that we don't
  					 * want to show.
  					 */
  					if (cp == (char *)(dp2 + 1))
  					    continue;
  					lp->d_partitions[8 + n++].p_fstype =
  					    FS_UNUSED;
  					break;
  
  				case DOSPTYP_LINUX:
  					pp->p_fstype = FS_EXT2FS;
  					n++;
  					break;
  
  				case DOSPTYP_FAT12:
  				case DOSPTYP_FAT16S:
  				case DOSPTYP_FAT16B:
  				case DOSPTYP_FAT32:
  				case DOSPTYP_FAT32L:
  				case DOSPTYP_FAT16L:
  					pp->p_fstype = FS_MSDOS;
  					n++;
  					break;
  				case DOSPTYP_EXTEND:
  				case DOSPTYP_EXTENDL:
  					part_blkno = dp2->dp_start + extoff;
  					if (!extoff)
  						extoff = dp2->dp_start;
  					wander = 1;
  					break;
  				default:
  					pp->p_fstype = FS_OTHER;
  					n++;
  					break;
  				}
  			}
  		}
  		lp->d_bbsize = 8192;
  		lp->d_sbsize = 64*1024;		/* XXX ? */
  		lp->d_npartitions = n > 0 ? n + 8 : 3;
  	}
  
  	/* record the OpenBSD partition's placement for the caller */
  	if (partoffp)
  		*partoffp = dospartoff;
  	if (cylp)
  		*cylp = cyl;
  
  	/* next, dig out disk label */
  	msg = readbsdlabel(bp, strat, cyl, dospartoff + I386_LABELSECTOR, -1,
  	    LITTLE_ENDIAN, lp, spoofonly);
  	if (msg)
  		return (msg);
  
  	/* obtain bad sector table if requested and present */
  	if (bdp && (lp->d_flags & D_BADSECT)) {
  		/*
  		 * get a new buffer and initialize it as callers trust the
  		 * buffer given to us, to point at the disklabel sector.
  		 */
  		dev = bp->b_dev;
  		bp = geteblk((int)lp->d_secsize);
  		bp->b_dev = dev;
  
  		i = 0;
  		do {
  			/* read a bad sector table */
  			bp->b_flags = B_BUSY | B_READ;
  			bp->b_blkno = lp->d_secperunit - lp->d_nsectors + i;
  			if (lp->d_secsize > DEV_BSIZE)
  				bp->b_blkno *= lp->d_secsize / DEV_BSIZE;
  			else
  				bp->b_blkno /= DEV_BSIZE / lp->d_secsize;
  			bp->b_bcount = lp->d_secsize;
  			bp->b_cylinder = lp->d_ncylinders - 1;
  			(*strat)(bp);
  
  			/* if successful, validate, otherwise try another */
  			if (biowait(bp))
  				msg = "bad sector table I/O error";
  			else {
  				db = (struct dkbad *)(bp->b_data);
  #define DKBAD_MAGIC 0x4321
  				if (db->bt_mbz == 0 &&
  				    db->bt_flag == DKBAD_MAGIC) {
  					msg = NULL;
  					*bdp = *db;
  					break;
  				} else
  					msg = "bad sector table corrupted";
  			}
  		} while ((bp->b_flags & B_ERROR) && (i += 2) < 10 &&
  		    i < lp->d_nsectors);
  
  		/* Give back the bad block buffer.  */
  		bp->b_flags |= B_INVAL;
  		brelse(bp);
  	}
  	return (msg);
  }
  #endif
  
  #if defined(DISKLABEL_AMIGA) || defined(DISKLABEL_ALL)
  /*
   * XXX RDB parsing is missing still.
   */
  char *
  readamigalabel(bp, strat, lp, osdep, spoofonly)
  	struct buf *bp;
  	void (*strat)(struct buf *);
  	struct disklabel *lp;
  	struct cpu_disklabel *osdep;
  	int spoofonly;
  {
  	char *msg;
  
  	msg = readbsdlabel(bp, strat, 0, AMIGA_LABELSECTOR, AMIGA_LABELOFFSET,
  	    BIG_ENDIAN, lp, spoofonly);
  	return (msg);
  }
  #endif
  
  /*
   * Check new disk label for sensibility
   * before setting it.
   */
  int
  setdisklabel(olp, nlp, openmask, osdep)
  	struct disklabel *olp, *nlp;
  	u_long openmask;
  	struct cpu_disklabel *osdep;
  {
  	int i;
  	struct partition *opp, *npp;
  
  	/* sanity clause */
  	if (nlp->d_secpercyl == 0 || nlp->d_secsize == 0 ||
  	    (nlp->d_secsize % DEV_BSIZE) != 0)
  		return(EINVAL);
  
  	/*
  	 * XXX Nice thought, but it doesn't work, if the intention was to
  	 * force a reread at the next *readdisklabel call.  That does not
  	 * happen.  There's still some use for it though as you can pseudo-
  	 * partition the disk.
  	 *
  	 * Special case to allow disklabel to be invalidated.
  	 */
  	if (nlp->d_magic == 0xffffffff) {
  		*olp = *nlp;
  		return (0);
  	}
  
  	if (nlp->d_magic != DISKMAGIC || nlp->d_magic2 != DISKMAGIC ||
  	    dkcksum(nlp) != 0)
  		return (EINVAL);
  
  	/* XXX missing check if other dos partitions will be overwritten */
  
  	while (openmask != 0) {
  		i = ffs((long)openmask) - 1;
  		openmask &= ~(1 << i);
  		if (nlp->d_npartitions <= i)
  			return (EBUSY);
  		opp = &olp->d_partitions[i];
  		npp = &nlp->d_partitions[i];
  		if (npp->p_offset != opp->p_offset ||
  		    npp->p_size < opp->p_size)
  			return (EBUSY);
  		/*
  		 * Copy internally-set partition information
  		 * if new label doesn't include it.		XXX
  		 */
  		if (npp->p_fstype == FS_UNUSED && opp->p_fstype != FS_UNUSED) {
  			npp->p_fstype = opp->p_fstype;
  			npp->p_fsize = opp->p_fsize;
  			npp->p_frag = opp->p_frag;
  			npp->p_cpg = opp->p_cpg;
  		}
  	}
  	nlp->d_checksum = 0;
  	nlp->d_checksum = dkcksum(nlp);
  	*olp = *nlp;
  	return (0);
  }
  
  
  /*
   * Write disk label back to device after modification.
   */
  int
  writedisklabel(dev, strat, lp, osdep)
  	dev_t dev;
  	void (*strat)(struct buf *);
  	struct disklabel *lp;
  	struct cpu_disklabel *osdep;
  {
  	enum disklabel_tag *tp;
  	char *msg = "no disk label";
  	struct buf *bp;
  	struct disklabel dl;
  #if defined(DISKLABEL_I386) || defined(DISKLABEL_ALL)
  	struct cpu_disklabel cdl;
  #endif
  	int labeloffset, error, i, endian, partoff = 0, cyl = 0;
  	u_int64_t csum, *p;
  
  	/* get a buffer and initialize it */
  	bp = geteblk((int)lp->d_secsize);
  	bp->b_dev = dev;
  
  	/*
  	 * I once played with the thought of using osdep->label{tag,sector}
  	 * as a cache for knowing where (and what) to write.  However, now I
  	 * think it might be useful to reprobe if someone has written
  	 * a newer disklabel of another type with disklabel(8) and -r.
  	 */
  	for (tp = probe_order; msg && *tp != -1; tp++) {
  		dl = *lp;
  		switch (*tp) {
  		case DLT_ALPHA:
  #if defined(DISKLABEL_ALPHA) || defined(DISKLABEL_ALL)
  			msg = readbsdlabel(bp, strat, 0, ALPHA_LABELSECTOR,
  			    ALPHA_LABELOFFSET, LITTLE_ENDIAN, &dl, 0);
  			labeloffset = ALPHA_LABELOFFSET;
  			endian = LITTLE_ENDIAN;
  #endif
  			break;
  
  		case DLT_I386:
  #if defined(DISKLABEL_I386) || defined(DISKLABEL_ALL)
  			msg = readdoslabel(bp, strat, &dl, &cdl, &partoff,
  			    &cyl, 0);
  			labeloffset = I386_LABELOFFSET;
  			endian = LITTLE_ENDIAN;
  #endif
  			break;
  
  		case DLT_AMIGA:
  #if defined(DISKLABEL_AMIGA) || defined(DISKLABEL_ALL)
  			msg = readamigalabel(bp, strat, &dl, &cdl, 0);
  			labeloffset = AMIGA_LABELOFFSET;
  			endian = BIG_ENDIAN;
  #endif
  			break;
  
  		default:
  			panic("unrecognized disklabel tag %d", *tp);
  		}
  	}
  
  	if (msg) {
  		if (partoff == -1)
  			return EIO;
  
  		/* Write it in the regular place with native byte order. */
  		labeloffset = LABELOFFSET;
  		endian = BYTE_ORDER;
  		bp->b_blkno = partoff + LABELSECTOR;
  		bp->b_cylinder = cyl;
  		bp->b_bcount = lp->d_secsize;
  	}
  
  	if (endian != BYTE_ORDER) {
  		swapdisklabel(lp);
  		/* recalc checksum */
  		lp->d_checksum = 0;
  		lp->d_checksum = dkcksum(lp);
  	}
  
  	*(struct disklabel *)(bp->b_data + labeloffset) = *lp;
  
  	/* Alpha bootblocks are checksummed.  */
  	if (*tp == DLT_ALPHA) {
  		for (csum = i = 0, p = (u_int64_t *)bp->b_data; i < 63; i++)
  			csum += *p++;
  		*p = csum;
  	}
  
  	bp->b_flags = B_BUSY | B_WRITE;
  	(*strat)(bp);
  	error = biowait(bp);
  
  	bp->b_flags |= B_INVAL;
  	brelse(bp);
  	return (error);
  }
  
  /*
   * Determine the size of the transfer, and make sure it is
   * within the boundaries of the partition. Adjust transfer
   * if needed, and signal errors or early completion.
   */
  int
  bounds_check_with_label(bp, lp, osdep, wlabel)
  	struct buf *bp;
  	struct disklabel *lp;
  	struct cpu_disklabel *osdep;
  	int wlabel;
  {
  #define blockpersec(count, lp) ((count) * (((lp)->d_secsize) / DEV_BSIZE))
  	struct partition *p = lp->d_partitions + DISKPART(bp->b_dev);
  	int labelsector = blockpersec(lp->d_partitions[RAW_PART].p_offset,
  	    lp) + osdep->labelsector;
  	int sz = howmany(bp->b_bcount, DEV_BSIZE);
  
  	/* avoid division by zero */
  	if (lp->d_secpercyl == 0) {
  		bp->b_error = EINVAL;
  		goto bad;
  	}
  
  	/* beyond partition? */
  	if (bp->b_blkno + sz > blockpersec(p->p_size, lp)) {
  		sz = blockpersec(p->p_size, lp) - bp->b_blkno;
  		if (sz == 0) {
  			/* If exactly at end of disk, return EOF. */
  			bp->b_resid = bp->b_bcount;
  			goto done;
  		}
  		if (sz < 0) {
  			/* If past end of disk, return EINVAL. */
  			bp->b_error = EINVAL;
  			goto bad;
  		}
  		/* Otherwise, truncate request. */
  		bp->b_bcount = sz << DEV_BSHIFT;
  	}
  
  	/* Overwriting disk label? */
  	if (bp->b_blkno + blockpersec(p->p_offset, lp) <= labelsector &&
  	    bp->b_blkno + blockpersec(p->p_offset, lp) + sz > labelsector &&
  	    (bp->b_flags & B_READ) == 0 && !wlabel) {
  		bp->b_error = EROFS;
  		goto bad;
  	}
  
  	/* calculate cylinder for disksort to order transfers with */
  	bp->b_cylinder = (bp->b_blkno + blockpersec(p->p_offset, lp)) /
  	    lp->d_secpercyl;
  	return (1);
  
  bad:
  	bp->b_flags |= B_ERROR;
  done:
  	return (0);
  }
  