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// 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)
* drew@Colorado.EDU
* +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 <asm/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)
{
struct address_space *mapping = bdev_whole(dev)->bd_inode->i_mapping;
unsigned char *res = NULL;
struct folio *folio;
folio = read_mapping_folio(mapping, 0, NULL);
if (IS_ERR(folio))
return NULL;
res = kmemdup(folio_address(folio) + 0x1be, 66, GFP_KERNEL);
folio_put(folio);
return res;
}
EXPORT_SYMBOL(scsi_bios_ptable);
/**
* 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])
{
int cyl, ext_cyl, end_head, end_cyl, end_sector;
unsigned int logical_end, physical_end, ext_physical_end;
struct msdos_partition *p, *largest = NULL;
void *buf;
int ret = false;
buf = scsi_bios_ptable(bdev);
if (!buf)
return false;
if (*(unsigned short *) (buf + 64) == 0xAA55) {
int largest_cyl = -1, i;
for (i = 0, p = buf; i < 4; i++, p++) {
if (!p->sys_ind)
continue;
#ifdef DEBUG
printk("scsicam_bios_param : partition %d has system \n",
i);
#endif
cyl = p->cyl + ((p->sector & 0xc0) << 2);
if (cyl > largest_cyl) {
largest_cyl = cyl;
largest = p;
}
}
}
if (largest) {
end_cyl = largest->end_cyl + ((largest->end_sector & 0xc0) << 2);
end_head = largest->end_head;
end_sector = largest->end_sector & 0x3f;
if (end_head + 1 == 0 || end_sector == 0)
goto out_free_buf;
#ifdef DEBUG
printk("scsicam_bios_param : end at h = %d, c = %d, s = %d\n",
end_head, end_cyl, end_sector);
#endif
physical_end = end_cyl * (end_head + 1) * end_sector +
end_head * end_sector + end_sector;
/* This is the actual _sector_ number at the end */
logical_end = get_unaligned_le32(&largest->start_sect)
+ get_unaligned_le32(&largest->nr_sects);
/* This is for >1023 cylinders */
ext_cyl = (logical_end - (end_head * end_sector + end_sector))
/ (end_head + 1) / end_sector;
ext_physical_end = ext_cyl * (end_head + 1) * end_sector +
end_head * end_sector + end_sector;
#ifdef DEBUG
printk("scsicam_bios_param : logical_end=%d physical_end=%d ext_physical_end=%d ext_cyl=%d\n"
,logical_end, physical_end, ext_physical_end, ext_cyl);
#endif
if (logical_end == physical_end ||
(end_cyl == 1023 && ext_physical_end == logical_end)) {
geom[0] = end_head + 1;
geom[1] = end_sector;
geom[2] = (unsigned long)capacity /
((end_head + 1) * end_sector);
ret = true;
goto out_free_buf;
}
#ifdef DEBUG
printk("scsicam_bios_param : logical (%u) != physical (%u)\n",
logical_end, physical_end);
#endif
}
out_free_buf:
kfree(buf);
return ret;
}
EXPORT_SYMBOL(scsi_partsize);
/*
* 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)
{
unsigned int rv = 0;
unsigned long heads, sectors, cylinders, temp;
cylinders = 1024L; /* Set number of cylinders to max */
sectors = 62L; /* Maximize sectors per track */
temp = cylinders * sectors; /* Compute divisor for heads */
heads = capacity / temp; /* Compute value for number of heads */
if (capacity % temp) { /* If no remainder, done! */
heads++; /* Else, increment number of heads */
temp = cylinders * heads; /* Compute divisor for sectors */
sectors = capacity / temp; /* Compute value for sectors per
track */
if (capacity % temp) { /* If no remainder, done! */
sectors++; /* Else, increment number of sectors */
temp = heads * sectors; /* Compute divisor for cylinders */
cylinders = capacity / temp; /* Compute number of cylinders */
}
}
if (cylinders == 0)
rv = (unsigned) -1; /* Give error if 0 cylinders */
*cyls = (unsigned int) cylinders; /* Stuff return values */
*secs = (unsigned int) sectors;
*hds = (unsigned int) heads;
return (rv);
}
/**
* 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)
{
u64 capacity64 = capacity; /* Suppress gcc warning */
int ret = 0;
/* try to infer mapping from partition table */
if (scsi_partsize(bdev, capacity, ip))
return 0;
if (capacity64 < (1ULL << 32)) {
/*
* Pick some standard mapping with at most 1024 cylinders, and
* at most 62 sectors per track - this works up to 7905 MB.
*/
ret = setsize((unsigned long)capacity, (unsigned int *)ip + 2,
(unsigned int *)ip + 0, (unsigned int *)ip + 1);
}
/*
* If something went wrong, then apparently we have to return a geometry
* with more than 1024 cylinders.
*/
if (ret || ip[0] > 255 || ip[1] > 63) {
if ((capacity >> 11) > 65534) {
ip[0] = 255;
ip[1] = 63;
} else {
ip[0] = 64;
ip[1] = 32;
}
if (capacity > 65535*63*255)
ip[2] = 65535;
else
ip[2] = (unsigned long)capacity / (ip[0] * ip[1]);
}
return 0;
}
EXPORT_SYMBOL(scsicam_bios_param);
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