This is xnu-8019. See this file in:
/*
 * Copyright (c) 2000-2002 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/*
 * HISTORY:
 * 16-Mar-88  John Seamons (jks) at NeXT
 *	Cleaned up to support standard disk label definitions.
 *
 * 24-Feb-88  Mike DeMoney (mike) at NeXT
 *	Added d_boot0_blkno to indicate logical block number
 *	of "block 0" boot.  This blkno is in d_secsize sectors.
 *	Added d_bootfile to indicate the default operating system
 *	image to be booted by the blk 0 boot.
 *	Changed d_name and d_type to be char arrays rather than ptrs
 *	so they are part of label.  This limits length of info in
 *	/etc/disktab, sorry.
 */

#ifndef _SYS_DISKTAB_
#define _SYS_DISKTAB_

#include <sys/appleapiopts.h>

#ifdef  __APPLE_API_OBSOLETE

/*
 * Disk description table, see disktab(5)
 */
#ifndef KERNEL
#define DISKTAB         "/etc/disktab"
#endif  /* !KERNEL */

#define MAXDNMLEN       24      // drive name length
#define MAXMPTLEN       16      // mount point length
#define MAXFSTLEN       8       // file system type length
#define MAXTYPLEN       24      // drive type length
#define NBOOTS          2       // # of boot blocks
#define MAXBFLEN        24      // bootfile name length
#define MAXHNLEN        32      // host name length
#define NPART           8       // # of partitions

typedef struct partition {
	int     p_base;         /* base sector# of partition */
	int     p_size;         /* #sectors in partition */
	short   p_bsize;        /* block size in bytes */
	short   p_fsize;        /* frag size in bytes */
	char    p_opt;          /* 's'pace/'t'ime optimization pref */
	short   p_cpg;          /* cylinders per group */
	short   p_density;      /* bytes per inode density */
	char    p_minfree;      /* minfree (%) */
	char    p_newfs;        /* run newfs during init */
	char    p_mountpt[MAXMPTLEN];/* mount point */
	char    p_automnt;      /* auto-mount when inserted */
	char    p_type[MAXFSTLEN];/* file system type */
} partition_t;

typedef struct disktab {
	char    d_name[MAXDNMLEN];      /* drive name */
	char    d_type[MAXTYPLEN];      /* drive type */
	int     d_secsize;              /* sector size in bytes */
	int     d_ntracks;              /* # tracks/cylinder */
	int     d_nsectors;             /* # sectors/track */
	int     d_ncylinders;           /* # cylinders */
	int     d_rpm;                  /* revolutions/minute */
	short   d_front;                /* size of front porch (sectors) */
	short   d_back;                 /* size of back porch (sectors) */
	short   d_ngroups;              /* number of alt groups */
	short   d_ag_size;              /* alt group size (sectors) */
	short   d_ag_alts;              /* alternate sectors / alt group */
	short   d_ag_off;               /* sector offset to first alternate */
	int     d_boot0_blkno[NBOOTS];  /* "blk 0" boot locations */
	char    d_bootfile[MAXBFLEN];   /* default bootfile */
	char    d_hostname[MAXHNLEN];   /* host name */
	char    d_rootpartition;        /* root partition e.g. 'a' */
	char    d_rwpartition;          /* r/w partition e.g. 'b' */
	partition_t d_partitions[NPART];
} disktab_t;

#ifndef KERNEL
struct  disktab *getdiskbyname(), *getdiskbydev();
#endif  /* !KERNEL */

#endif  /* __APPLE_API_OBSOLETE */

#endif  /* _SYS_DISKTAB_ */