hw/block/hd-geometry.c

   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 "qemu/bswap.h"
  36 #include "hw/block/block.h"
  37 #include "trace.h"
  38
  39 struct partition {
  40         uint8_t boot_ind;           /* 0x80 - active */
  41         uint8_t head;               /* starting head */
  42         uint8_t sector;             /* starting sector */
  43         uint8_t cyl;                /* starting cylinder */
  44         uint8_t sys_ind;            /* What partition type */
  45         uint8_t end_head;           /* end head */
  46         uint8_t end_sector;         /* end sector */
  47         uint8_t end_cyl;            /* end cylinder */
  48         uint32_t start_sect;        /* starting sector counting from 0 */
  49         uint32_t nr_sects;          /* nr of sectors in partition */
  50 } QEMU_PACKED;
  51
  52 /* try to guess the disk logical geometry from the MSDOS partition table.
  53    Return 0 if OK, -1 if could not guess */
  54 static int guess_disk_lchs(BlockBackend *blk,
  55                            int *pcylinders, int *pheads, int *psectors)
  56 {
  57     uint8_t buf[BDRV_SECTOR_SIZE];
  58     int i, heads, sectors, cylinders;
  59     struct partition *p;
  60     uint32_t nr_sects;
  61     uint64_t nb_sectors;
  62
  63     blk_get_geometry(blk, &nb_sectors);
  64
  65     /**
  66      * The function will be invoked during startup not only in sync I/O mode,
  67      * but also in async I/O mode. So the I/O throttling function has to
  68      * be disabled temporarily here, not permanently.
  69      */
  70     if (blk_pread_unthrottled(blk, 0, buf, BDRV_SECTOR_SIZE) < 0) {
  71         return -1;
  72     }
  73     /* test msdos magic */
  74     if (buf[510] != 0x55 || buf[511] != 0xaa) {
  75         return -1;
  76     }
  77     for (i = 0; i < 4; i++) {
  78         p = ((struct partition *)(buf + 0x1be)) + i;
  79         nr_sects = le32_to_cpu(p->nr_sects);
  80         if (nr_sects && p->end_head) {
  81             /* We make the assumption that the partition terminates on
  82                a cylinder boundary */
  83             heads = p->end_head + 1;
  84             sectors = p->end_sector & 63;
  85             if (sectors == 0) {
  86                 continue;
  87             }
  88             cylinders = nb_sectors / (heads * sectors);
  89             if (cylinders < 1 || cylinders > 16383) {
  90                 continue;
  91             }
  92             *pheads = heads;
  93             *psectors = sectors;
  94             *pcylinders = cylinders;
  95             trace_hd_geometry_lchs_guess(blk, cylinders, heads, sectors);
  96             return 0;
  97         }
  98     }
  99     return -1;
 100 }
 101
 102 static void guess_chs_for_size(BlockBackend *blk,
 103                 uint32_t *pcyls, uint32_t *pheads, uint32_t *psecs)
 104 {
 105     uint64_t nb_sectors;
 106     int cylinders;
 107
 108     blk_get_geometry(blk, &nb_sectors);
 109
 110     cylinders = nb_sectors / (16 * 63);
 111     if (cylinders > 16383) {
 112         cylinders = 16383;
 113     } else if (cylinders < 2) {
 114         cylinders = 2;
 115     }
 116     *pcyls = cylinders;
 117     *pheads = 16;
 118     *psecs = 63;
 119 }
 120
 121 void hd_geometry_guess(BlockBackend *blk,
 122                        uint32_t *pcyls, uint32_t *pheads, uint32_t *psecs,
 123                        int *ptrans)
 124 {
 125     int cylinders, heads, secs, translation;
 126     HDGeometry geo;
 127
 128     /* Try to probe the backing device geometry, otherwise fallback
 129        to the old logic. (as of 12/2014 probing only succeeds on DASDs) */
 130     if (blk_probe_geometry(blk, &geo) == 0) {
 131         *pcyls = geo.cylinders;
 132         *psecs = geo.sectors;
 133         *pheads = geo.heads;
 134         translation = BIOS_ATA_TRANSLATION_NONE;
 135     } else if (guess_disk_lchs(blk, &cylinders, &heads, &secs) < 0) {
 136         /* no LCHS guess: use a standard physical disk geometry  */
 137         guess_chs_for_size(blk, pcyls, pheads, psecs);
 138         translation = hd_bios_chs_auto_trans(*pcyls, *pheads, *psecs);
 139     } else if (heads > 16) {
 140         /* LCHS guess with heads > 16 means that a BIOS LBA
 141            translation was active, so a standard physical disk
 142            geometry is OK */
 143         guess_chs_for_size(blk, pcyls, pheads, psecs);
 144         translation = *pcyls * *pheads <= 131072
 145             ? BIOS_ATA_TRANSLATION_LARGE
 146             : BIOS_ATA_TRANSLATION_LBA;
 147     } else {
 148         /* LCHS guess with heads <= 16: use as physical geometry */
 149         *pcyls = cylinders;
 150         *pheads = heads;
 151         *psecs = secs;
 152         /* disable any translation to be in sync with
 153            the logical geometry */
 154         translation = BIOS_ATA_TRANSLATION_NONE;
 155     }
 156     if (ptrans) {
 157         *ptrans = translation;
 158     }
 159     trace_hd_geometry_guess(blk, *pcyls, *pheads, *psecs, translation);
 160 }
 161
 162 int hd_bios_chs_auto_trans(uint32_t cyls, uint32_t heads, uint32_t secs)
 163 {
 164     return cyls <= 1024 && heads <= 16 && secs <= 63
 165         ? BIOS_ATA_TRANSLATION_NONE
 166         : BIOS_ATA_TRANSLATION_LBA;
 167 }