linux/drivers/scsi/scsicam.c

// SPDX-License-Identifier: GPL-2.0
/*
 * scsicam.c - SCSI CAM support functions, use for HDIO_GETGEO, etc.
 *
 * Copyright 1993, 1994 Drew Eckhardt
 *      Visionary Computing 
 *      (Unix and Linux consulting and custom programming)
 *      [email protected]
 *      +1 (303) 786-7975
 *
 * For more information, please consult the SCSI-CAM draft.
 */

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/blkdev.h>
#include <linux/pagemap.h>
#include <linux/msdos_partition.h>
#include <linux/unaligned.h>

#include <scsi/scsicam.h>

/**
 * scsi_bios_ptable - Read PC partition table out of first sector of device.
 * @dev: from this device
 *
 * Description: Reads the first sector from the device and returns %0x42 bytes
 *              starting at offset %0x1be.
 * Returns: partition table in kmalloc(GFP_KERNEL) memory, or NULL on error.
 */
unsigned char *scsi_bios_ptable(struct block_device *dev)
{ … }
EXPORT_SYMBOL(…);

/**
 * scsi_partsize - Parse cylinders/heads/sectors from PC partition table
 * @bdev: block device to parse
 * @capacity: size of the disk in sectors
 * @geom: output in form of [hds, cylinders, sectors]
 *
 * Determine the BIOS mapping/geometry used to create the partition
 * table, storing the results in @geom.
 *
 * Returns: %false on failure, %true on success.
 */
bool scsi_partsize(struct block_device *bdev, sector_t capacity, int geom[3])
{ … }
EXPORT_SYMBOL(…);

/*
 * Function : static int setsize(unsigned long capacity,unsigned int *cyls,
 *      unsigned int *hds, unsigned int *secs);
 *
 * Purpose : to determine a near-optimal int 0x13 mapping for a
 *      SCSI disk in terms of lost space of size capacity, storing
 *      the results in *cyls, *hds, and *secs.
 *
 * Returns : -1 on failure, 0 on success.
 *
 * Extracted from
 *
 * WORKING                                                    X3T9.2
 * DRAFT                                                        792D
 * see http://www.t10.org/ftp/t10/drafts/cam/cam-r12b.pdf
 *
 *                                                        Revision 6
 *                                                         10-MAR-94
 * Information technology -
 * SCSI-2 Common access method
 * transport and SCSI interface module
 * 
 * ANNEX A :
 *
 * setsize() converts a read capacity value to int 13h
 * head-cylinder-sector requirements. It minimizes the value for
 * number of heads and maximizes the number of cylinders. This
 * will support rather large disks before the number of heads
 * will not fit in 4 bits (or 6 bits). This algorithm also
 * minimizes the number of sectors that will be unused at the end
 * of the disk while allowing for very large disks to be
 * accommodated. This algorithm does not use physical geometry. 
 */

static int setsize(unsigned long capacity, unsigned int *cyls, unsigned int *hds,
		   unsigned int *secs)
{ … }

/**
 * scsicam_bios_param - Determine geometry of a disk in cylinders/heads/sectors.
 * @bdev: which device
 * @capacity: size of the disk in sectors
 * @ip: return value: ip[0]=heads, ip[1]=sectors, ip[2]=cylinders
 *
 * Description : determine the BIOS mapping/geometry used for a drive in a
 *      SCSI-CAM system, storing the results in ip as required
 *      by the HDIO_GETGEO ioctl().
 *
 * Returns : -1 on failure, 0 on success.
 */
int scsicam_bios_param(struct block_device *bdev, sector_t capacity, int *ip)
{ … }
EXPORT_SYMBOL(…);