plugins/partitioning/partition-mbr.c

   1 /* nbdkit
   2  * Copyright Red Hat
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions are
   6  * met:
   7  *
   8  * * Redistributions of source code must retain the above copyright
   9  * notice, this list of conditions and the following disclaimer.
  10  *
  11  * * Redistributions in binary form must reproduce the above copyright
  12  * notice, this list of conditions and the following disclaimer in the
  13  * documentation and/or other materials provided with the distribution.
  14  *
  15  * * Neither the name of Red Hat nor the names of its contributors may be
  16  * used to endorse or promote products derived from this software without
  17  * specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
  20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
  21  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
  22  * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
  23  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  24  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  25  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
  26  * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  27  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  28  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  29  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  */
  32
  33 #include <config.h>
  34
  35 #include <stdio.h>
  36 #include <stdlib.h>
  37 #include <stdbool.h>
  38 #include <string.h>
  39 #include <inttypes.h>
  40 #include <assert.h>
  41
  42 #include <nbdkit-plugin.h>
  43
  44 #include "byte-swapping.h"
  45
  46 #include "isaligned.h"
  47 #include "rounding.h"
  48
  49 #include "regions.h"
  50 #include "virtual-disk.h"
  51
  52 static const struct region *find_file_region (size_t i, size_t *j);
  53 static const struct region *find_ebr_region (size_t i, size_t *j);
  54
  55 /* Create the MBR and optionally EBRs. */
  56 void
  57 create_mbr_layout (void)
  58 {
  59   size_t i, j = 0;
  60
  61   /* Boot signature. */
  62   primary[0x1fe] = 0x55;
  63   primary[0x1ff] = 0xaa;
  64
  65   if (the_files.len <= 4) {
  66     /* Basic MBR with no extended partition. */
  67     for (i = 0; i < the_files.len; ++i) {
  68       const struct region *region = find_file_region (i, &j);
  69
  70       create_mbr_partition_table_entry (region, i == 0, the_files.ptr[i].mbr_id,
  71                                         &primary[0x1be + 16*i]);
  72     }
  73   }
  74   else {
  75     struct region region;
  76     const struct region *rptr, *eptr0, *eptr;
  77
  78     /* The first three primary partitions correspond to the first
  79      * three files.
  80      */
  81     for (i = 0; i < 3; ++i) {
  82       rptr = find_file_region (i, &j);
  83       create_mbr_partition_table_entry (rptr, i == 0, the_files.ptr[i].mbr_id,
  84                                         &primary[0x1be + 16*i]);
  85     }
  86
  87     /* The fourth partition is an extended PTE and does not correspond
  88      * to any file.  This partition starts with the first EBR, so find
  89      * it.  The partition extends to the end of the disk.
  90      */
  91     eptr0 = find_ebr_region (3, &j);
  92     region.start = eptr0->start;
  93     region.end = virtual_size (&the_regions) - 1; /* to end of disk */
  94     region.len = region.end - region.start + 1;
  95     create_mbr_partition_table_entry (&region, false, 0xf, &primary[0x1ee]);
  96
  97     /* The remaining files are mapped to logical partitions living in
  98      * the fourth extended partition.
  99      */
 100     for (i = 3; i < the_files.len; ++i) {
 101       if (i == 3)
 102         eptr = eptr0;
 103       else
 104         eptr = find_ebr_region (i, &j);
 105       rptr = find_file_region (i, &j);
 106
 107       /* Signature. */
 108       ebr[i-3][0x1fe] = 0x55;
 109       ebr[i-3][0x1ff] = 0xaa;
 110
 111       /* First entry in EBR contains:
 112        * offset from EBR sector to the first sector of the logical partition
 113        * total count of sectors in the logical partition
 114        */
 115       region.start = rptr->start - eptr->start;
 116       region.len = rptr->len;
 117       create_mbr_partition_table_entry (&region, false, the_files.ptr[i].mbr_id,
 118                                         &ebr[i-3][0x1be]);
 119
 120       if (i < the_files.len-1) {
 121         size_t j2 = j;
 122         const struct region *enext = find_ebr_region (i+1, &j2);
 123         const struct region *rnext = find_file_region (i+1, &j2);
 124
 125         /* Second entry in the EBR contains:
 126          * address of next EBR relative to extended partition
 127          * total count of sectors in the next logical partition including
 128          * next EBR
 129          */
 130         region.start = enext->start - eptr0->start;
 131         region.len = rnext->end - enext->start + 1;
 132         create_mbr_partition_table_entry (&region, false, 0xf,
 133                                           &ebr[i-3][0x1ce]);
 134       }
 135     }
 136   }
 137 }
 138
 139 /* Find the region corresponding to file[i].
 140  * j is a scratch register ensuring we only do a linear scan.
 141  */
 142 static const struct region *
 143 find_file_region (size_t i, size_t *j)
 144 {
 145   const struct region *region;
 146
 147   for (; *j < nr_regions (&the_regions); ++(*j)) {
 148     region = &the_regions.ptr[*j];
 149     if (region->type == region_file && region->u.i == i)
 150       return region;
 151   }
 152   abort ();
 153 }
 154
 155 /* Find the region corresponding to EBR of file[i] (i >= 3).
 156  * j is a scratch register ensuring we only do a linear scan.
 157  */
 158 static const struct region *
 159 find_ebr_region (size_t i, size_t *j)
 160 {
 161   const struct region *region;
 162
 163   assert (i >= 3);
 164
 165   for (; *j < nr_regions (&the_regions); ++(*j)) {
 166     region = &the_regions.ptr[*j];
 167     if (region->type == region_data && region->u.data == ebr[i-3])
 168       return region;
 169   }
 170   abort ();
 171 }
 172
 173 static void
 174 chs_too_large (unsigned char *out)
 175 {
 176   const int c = 1023, h = 254, s = 63;
 177
 178   out[0] = h;
 179   out[1] = (c & 0x300) >> 2 | s;
 180   out[2] = c & 0xff;
 181 }
 182
 183 void
 184 create_mbr_partition_table_entry (const struct region *region,
 185                                   bool bootable, int partition_id,
 186                                   unsigned char *out)
 187 {
 188   uint64_t start_sector, nr_sectors;
 189   uint32_t u32;
 190
 191   assert (IS_ALIGNED (region->start, SECTOR_SIZE));
 192
 193   start_sector = region->start / SECTOR_SIZE;
 194   nr_sectors = DIV_ROUND_UP (region->len, SECTOR_SIZE);
 195
 196   /* The total_size test in partitioning_config_complete should catch
 197    * this earlier.
 198    */
 199   assert (start_sector <= UINT32_MAX);
 200   assert (nr_sectors <= UINT32_MAX);
 201
 202   out[0] = bootable ? 0x80 : 0;
 203   chs_too_large (&out[1]);
 204   out[4] = partition_id;
 205   chs_too_large (&out[5]);
 206   u32 = htole32 (start_sector);
 207   memcpy (&out[8], &u32, 4);
 208   u32 = htole32 (nr_sectors);
 209   memcpy (&out[12], &u32, 4);
 210 }