xref: /openbmc/qemu/hw/block/hd-geometry.c (revision 2e1cacfb)
1 /*
2  * Hard disk geometry utilities
3  *
4  * Copyright (C) 2012 Red Hat, Inc.
5  *
6  * This work is licensed under the terms of the GNU GPL, version 2 or later.
7  * See the COPYING file in the top-level directory.
8  *
9  * This file incorporates work covered by the following copyright and
10  * permission notice:
11  *
12  * Copyright (c) 2003 Fabrice Bellard
13  *
14  * Permission is hereby granted, free of charge, to any person obtaining a copy
15  * of this software and associated documentation files (the "Software"), to deal
16  * in the Software without restriction, including without limitation the rights
17  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
18  * copies of the Software, and to permit persons to whom the Software is
19  * furnished to do so, subject to the following conditions:
20  *
21  * The above copyright notice and this permission notice shall be included in
22  * all copies or substantial portions of the Software.
23  *
24  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
25  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
26  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
27  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
28  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
29  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
30  * THE SOFTWARE.
31  */
32 
33 #include "qemu/osdep.h"
34 #include "sysemu/block-backend.h"
35 #include "qapi/qapi-types-block.h"
36 #include "qemu/bswap.h"
37 #include "hw/block/block.h"
38 #include "trace.h"
39 
40 struct partition {
41         uint8_t boot_ind;           /* 0x80 - active */
42         uint8_t head;               /* starting head */
43         uint8_t sector;             /* starting sector */
44         uint8_t cyl;                /* starting cylinder */
45         uint8_t sys_ind;            /* What partition type */
46         uint8_t end_head;           /* end head */
47         uint8_t end_sector;         /* end sector */
48         uint8_t end_cyl;            /* end cylinder */
49         uint32_t start_sect;        /* starting sector counting from 0 */
50         uint32_t nr_sects;          /* nr of sectors in partition */
51 } QEMU_PACKED;
52 
53 /* try to guess the disk logical geometry from the MS-DOS partition table.
54    Return 0 if OK, -1 if could not guess */
55 static int guess_disk_lchs(BlockBackend *blk,
56                            int *pcylinders, int *pheads, int *psectors)
57 {
58     uint8_t buf[BDRV_SECTOR_SIZE];
59     int i, heads, sectors, cylinders;
60     struct partition *p;
61     uint32_t nr_sects;
62     uint64_t nb_sectors;
63 
64     blk_get_geometry(blk, &nb_sectors);
65 
66     if (blk_pread(blk, 0, BDRV_SECTOR_SIZE, buf, 0) < 0) {
67         return -1;
68     }
69     /* test MS-DOS magic */
70     if (buf[510] != 0x55 || buf[511] != 0xaa) {
71         return -1;
72     }
73     for (i = 0; i < 4; i++) {
74         p = ((struct partition *)(buf + 0x1be)) + i;
75         nr_sects = le32_to_cpu(p->nr_sects);
76         if (nr_sects && p->end_head) {
77             /* We make the assumption that the partition terminates on
78                a cylinder boundary */
79             heads = p->end_head + 1;
80             sectors = p->end_sector & 63;
81             if (sectors == 0) {
82                 continue;
83             }
84             cylinders = nb_sectors / (heads * sectors);
85             if (cylinders < 1 || cylinders > 16383) {
86                 continue;
87             }
88             *pheads = heads;
89             *psectors = sectors;
90             *pcylinders = cylinders;
91             trace_hd_geometry_lchs_guess(blk, cylinders, heads, sectors);
92             return 0;
93         }
94     }
95     return -1;
96 }
97 
98 static void guess_chs_for_size(BlockBackend *blk,
99                 uint32_t *pcyls, uint32_t *pheads, uint32_t *psecs)
100 {
101     uint64_t nb_sectors;
102     int cylinders;
103 
104     blk_get_geometry(blk, &nb_sectors);
105 
106     cylinders = nb_sectors / (16 * 63);
107     if (cylinders > 16383) {
108         cylinders = 16383;
109     } else if (cylinders < 2) {
110         cylinders = 2;
111     }
112     *pcyls = cylinders;
113     *pheads = 16;
114     *psecs = 63;
115 }
116 
117 void hd_geometry_guess(BlockBackend *blk,
118                        uint32_t *pcyls, uint32_t *pheads, uint32_t *psecs,
119                        int *ptrans)
120 {
121     int cylinders, heads, secs, translation;
122     HDGeometry geo;
123 
124     /* Try to probe the backing device geometry, otherwise fallback
125        to the old logic. (as of 12/2014 probing only succeeds on DASDs) */
126     if (blk_probe_geometry(blk, &geo) == 0) {
127         *pcyls = geo.cylinders;
128         *psecs = geo.sectors;
129         *pheads = geo.heads;
130         translation = BIOS_ATA_TRANSLATION_NONE;
131     } else if (guess_disk_lchs(blk, &cylinders, &heads, &secs) < 0) {
132         /* no LCHS guess: use a standard physical disk geometry  */
133         guess_chs_for_size(blk, pcyls, pheads, psecs);
134         translation = hd_bios_chs_auto_trans(*pcyls, *pheads, *psecs);
135     } else if (heads > 16) {
136         /* LCHS guess with heads > 16 means that a BIOS LBA
137            translation was active, so a standard physical disk
138            geometry is OK */
139         guess_chs_for_size(blk, pcyls, pheads, psecs);
140         translation = *pcyls * *pheads <= 131072
141             ? BIOS_ATA_TRANSLATION_LARGE
142             : BIOS_ATA_TRANSLATION_LBA;
143     } else {
144         /* LCHS guess with heads <= 16: use as physical geometry */
145         *pcyls = cylinders;
146         *pheads = heads;
147         *psecs = secs;
148         /* disable any translation to be in sync with
149            the logical geometry */
150         translation = BIOS_ATA_TRANSLATION_NONE;
151     }
152     if (ptrans) {
153         if (*ptrans == BIOS_ATA_TRANSLATION_AUTO) {
154             *ptrans = translation;
155         } else {
156             /* Defer to the translation specified by the user.  */
157             translation = *ptrans;
158         }
159     }
160     trace_hd_geometry_guess(blk, *pcyls, *pheads, *psecs, translation);
161 }
162 
163 int hd_bios_chs_auto_trans(uint32_t cyls, uint32_t heads, uint32_t secs)
164 {
165     return cyls <= 1024 && heads <= 16 && secs <= 63
166         ? BIOS_ATA_TRANSLATION_NONE
167         : BIOS_ATA_TRANSLATION_LBA;
168 }
169