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