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 | */ |
33 | unsigned 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, index: 0, NULL); |
40 | if (IS_ERR(ptr: folio)) |
41 | return NULL; |
42 | |
43 | res = kmemdup(p: folio_address(folio) + 0x1be, size: 66, GFP_KERNEL); |
44 | folio_put(folio); |
45 | return res; |
46 | } |
47 | EXPORT_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 | */ |
60 | bool 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(p: &largest->start_sect) |
107 | + get_unaligned_le32(p: &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 | |
135 | out_free_buf: |
136 | kfree(objp: buf); |
137 | return ret; |
138 | } |
139 | EXPORT_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 | |
175 | static 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 | */ |
218 | int 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(capacity: (unsigned long)capacity, cyls: (unsigned int *)ip + 2, |
233 | hds: (unsigned int *)ip + 0, secs: (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 | } |
257 | EXPORT_SYMBOL(scsicam_bios_param); |
258 | |