scsicam.c (7748B)
1// SPDX-License-Identifier: GPL-2.0 2/* 3 * scsicam.c - SCSI CAM support functions, use for HDIO_GETGEO, etc. 4 * 5 * Copyright 1993, 1994 Drew Eckhardt 6 * Visionary Computing 7 * (Unix and Linux consulting and custom programming) 8 * drew@Colorado.EDU 9 * +1 (303) 786-7975 10 * 11 * For more information, please consult the SCSI-CAM draft. 12 */ 13 14#include <linux/module.h> 15#include <linux/slab.h> 16#include <linux/fs.h> 17#include <linux/kernel.h> 18#include <linux/blkdev.h> 19#include <linux/pagemap.h> 20#include <linux/msdos_partition.h> 21#include <asm/unaligned.h> 22 23#include <scsi/scsicam.h> 24 25/** 26 * scsi_bios_ptable - Read PC partition table out of first sector of device. 27 * @dev: from this device 28 * 29 * Description: Reads the first sector from the device and returns %0x42 bytes 30 * starting at offset %0x1be. 31 * Returns: partition table in kmalloc(GFP_KERNEL) memory, or NULL on error. 32 */ 33unsigned char *scsi_bios_ptable(struct block_device *dev) 34{ 35 struct address_space *mapping = bdev_whole(dev)->bd_inode->i_mapping; 36 unsigned char *res = NULL; 37 struct folio *folio; 38 39 folio = read_mapping_folio(mapping, 0, NULL); 40 if (IS_ERR(folio)) 41 return NULL; 42 43 res = kmemdup(folio_address(folio) + 0x1be, 66, GFP_KERNEL); 44 folio_put(folio); 45 return res; 46} 47EXPORT_SYMBOL(scsi_bios_ptable); 48 49/** 50 * scsi_partsize - Parse cylinders/heads/sectors from PC partition table 51 * @bdev: block device to parse 52 * @capacity: size of the disk in sectors 53 * @geom: output in form of [hds, cylinders, sectors] 54 * 55 * Determine the BIOS mapping/geometry used to create the partition 56 * table, storing the results in @geom. 57 * 58 * Returns: %false on failure, %true on success. 59 */ 60bool scsi_partsize(struct block_device *bdev, sector_t capacity, int geom[3]) 61{ 62 int cyl, ext_cyl, end_head, end_cyl, end_sector; 63 unsigned int logical_end, physical_end, ext_physical_end; 64 struct msdos_partition *p, *largest = NULL; 65 void *buf; 66 int ret = false; 67 68 buf = scsi_bios_ptable(bdev); 69 if (!buf) 70 return false; 71 72 if (*(unsigned short *) (buf + 64) == 0xAA55) { 73 int largest_cyl = -1, i; 74 75 for (i = 0, p = buf; i < 4; i++, p++) { 76 if (!p->sys_ind) 77 continue; 78#ifdef DEBUG 79 printk("scsicam_bios_param : partition %d has system \n", 80 i); 81#endif 82 cyl = p->cyl + ((p->sector & 0xc0) << 2); 83 if (cyl > largest_cyl) { 84 largest_cyl = cyl; 85 largest = p; 86 } 87 } 88 } 89 if (largest) { 90 end_cyl = largest->end_cyl + ((largest->end_sector & 0xc0) << 2); 91 end_head = largest->end_head; 92 end_sector = largest->end_sector & 0x3f; 93 94 if (end_head + 1 == 0 || end_sector == 0) 95 goto out_free_buf; 96 97#ifdef DEBUG 98 printk("scsicam_bios_param : end at h = %d, c = %d, s = %d\n", 99 end_head, end_cyl, end_sector); 100#endif 101 102 physical_end = end_cyl * (end_head + 1) * end_sector + 103 end_head * end_sector + end_sector; 104 105 /* This is the actual _sector_ number at the end */ 106 logical_end = get_unaligned_le32(&largest->start_sect) 107 + get_unaligned_le32(&largest->nr_sects); 108 109 /* This is for >1023 cylinders */ 110 ext_cyl = (logical_end - (end_head * end_sector + end_sector)) 111 / (end_head + 1) / end_sector; 112 ext_physical_end = ext_cyl * (end_head + 1) * end_sector + 113 end_head * end_sector + end_sector; 114 115#ifdef DEBUG 116 printk("scsicam_bios_param : logical_end=%d physical_end=%d ext_physical_end=%d ext_cyl=%d\n" 117 ,logical_end, physical_end, ext_physical_end, ext_cyl); 118#endif 119 120 if (logical_end == physical_end || 121 (end_cyl == 1023 && ext_physical_end == logical_end)) { 122 geom[0] = end_head + 1; 123 geom[1] = end_sector; 124 geom[2] = (unsigned long)capacity / 125 ((end_head + 1) * end_sector); 126 ret = true; 127 goto out_free_buf; 128 } 129#ifdef DEBUG 130 printk("scsicam_bios_param : logical (%u) != physical (%u)\n", 131 logical_end, physical_end); 132#endif 133 } 134 135out_free_buf: 136 kfree(buf); 137 return ret; 138} 139EXPORT_SYMBOL(scsi_partsize); 140 141/* 142 * Function : static int setsize(unsigned long capacity,unsigned int *cyls, 143 * unsigned int *hds, unsigned int *secs); 144 * 145 * Purpose : to determine a near-optimal int 0x13 mapping for a 146 * SCSI disk in terms of lost space of size capacity, storing 147 * the results in *cyls, *hds, and *secs. 148 * 149 * Returns : -1 on failure, 0 on success. 150 * 151 * Extracted from 152 * 153 * WORKING X3T9.2 154 * DRAFT 792D 155 * see http://www.t10.org/ftp/t10/drafts/cam/cam-r12b.pdf 156 * 157 * Revision 6 158 * 10-MAR-94 159 * Information technology - 160 * SCSI-2 Common access method 161 * transport and SCSI interface module 162 * 163 * ANNEX A : 164 * 165 * setsize() converts a read capacity value to int 13h 166 * head-cylinder-sector requirements. It minimizes the value for 167 * number of heads and maximizes the number of cylinders. This 168 * will support rather large disks before the number of heads 169 * will not fit in 4 bits (or 6 bits). This algorithm also 170 * minimizes the number of sectors that will be unused at the end 171 * of the disk while allowing for very large disks to be 172 * accommodated. This algorithm does not use physical geometry. 173 */ 174 175static int setsize(unsigned long capacity, unsigned int *cyls, unsigned int *hds, 176 unsigned int *secs) 177{ 178 unsigned int rv = 0; 179 unsigned long heads, sectors, cylinders, temp; 180 181 cylinders = 1024L; /* Set number of cylinders to max */ 182 sectors = 62L; /* Maximize sectors per track */ 183 184 temp = cylinders * sectors; /* Compute divisor for heads */ 185 heads = capacity / temp; /* Compute value for number of heads */ 186 if (capacity % temp) { /* If no remainder, done! */ 187 heads++; /* Else, increment number of heads */ 188 temp = cylinders * heads; /* Compute divisor for sectors */ 189 sectors = capacity / temp; /* Compute value for sectors per 190 track */ 191 if (capacity % temp) { /* If no remainder, done! */ 192 sectors++; /* Else, increment number of sectors */ 193 temp = heads * sectors; /* Compute divisor for cylinders */ 194 cylinders = capacity / temp; /* Compute number of cylinders */ 195 } 196 } 197 if (cylinders == 0) 198 rv = (unsigned) -1; /* Give error if 0 cylinders */ 199 200 *cyls = (unsigned int) cylinders; /* Stuff return values */ 201 *secs = (unsigned int) sectors; 202 *hds = (unsigned int) heads; 203 return (rv); 204} 205 206/** 207 * scsicam_bios_param - Determine geometry of a disk in cylinders/heads/sectors. 208 * @bdev: which device 209 * @capacity: size of the disk in sectors 210 * @ip: return value: ip[0]=heads, ip[1]=sectors, ip[2]=cylinders 211 * 212 * Description : determine the BIOS mapping/geometry used for a drive in a 213 * SCSI-CAM system, storing the results in ip as required 214 * by the HDIO_GETGEO ioctl(). 215 * 216 * Returns : -1 on failure, 0 on success. 217 */ 218int scsicam_bios_param(struct block_device *bdev, sector_t capacity, int *ip) 219{ 220 u64 capacity64 = capacity; /* Suppress gcc warning */ 221 int ret = 0; 222 223 /* try to infer mapping from partition table */ 224 if (scsi_partsize(bdev, capacity, ip)) 225 return 0; 226 227 if (capacity64 < (1ULL << 32)) { 228 /* 229 * Pick some standard mapping with at most 1024 cylinders, and 230 * at most 62 sectors per track - this works up to 7905 MB. 231 */ 232 ret = setsize((unsigned long)capacity, (unsigned int *)ip + 2, 233 (unsigned int *)ip + 0, (unsigned int *)ip + 1); 234 } 235 236 /* 237 * If something went wrong, then apparently we have to return a geometry 238 * with more than 1024 cylinders. 239 */ 240 if (ret || ip[0] > 255 || ip[1] > 63) { 241 if ((capacity >> 11) > 65534) { 242 ip[0] = 255; 243 ip[1] = 63; 244 } else { 245 ip[0] = 64; 246 ip[1] = 32; 247 } 248 249 if (capacity > 65535*63*255) 250 ip[2] = 65535; 251 else 252 ip[2] = (unsigned long)capacity / (ip[0] * ip[1]); 253 } 254 255 return 0; 256} 257EXPORT_SYMBOL(scsicam_bios_param);