com32/gpllib/disk/msdos.c

   1 /* ----------------------------------------------------------------------- *
   2  *
   3  *   Copyright 2009 Pierre-Alexandre Meyer
   4  *
   5  *   Some parts borrowed from chain.c32:
   6  *
   7  *   Copyright 2003-2009 H. Peter Anvin - All Rights Reserved
   8  *   Copyright 2009 Intel Corporation; author: H. Peter Anvin
   9  *
  10  *   This file is part of Syslinux, and is made available under
  11  *   the terms of the GNU General Public License version 2.
  12  *
  13  * ----------------------------------------------------------------------- */
  14
  15 #include <stdlib.h>
  16
  17 #include <disk/common.h>
  18 #include <disk/geom.h>
  19 #include <disk/msdos.h>
  20 #include <disk/partition.h>
  21 #include <disk/read.h>
  22
  23 static inline int is_extended_partition(struct part_entry *ptab)
  24 {
  25     return (ptab->ostype == 0x05 ||
  26             ptab->ostype == 0x0f || ptab->ostype == 0x85);
  27 }
  28
  29 static inline int msdos_magic_present(const char *ptab)
  30 {
  31     return (*(uint16_t *) (ptab + 0x1fe) == 0xaa55);
  32 }
  33
  34 /**
  35  * process_extended_partition - execute a callback for each partition contained listed in an ebr
  36  * @drive_info:         driveinfo struct describing the drive
  37  * @partition_offset:   Absolute start (lba) of the extended partition
  38  * @ebr_offset:         Relative start (lba) of the current ebr processed within
  39  *                      the extended partition
  40  * @callback:           Callback to execute
  41  * @error:              Buffer for I/O errors
  42  * @nb_part_seen:       Number of partitions found on the disk so far
  43  **/
  44 static int process_extended_partition(struct driveinfo *drive_info,
  45                                       const int partition_offset,
  46                                       const int ebr_offset,
  47                                       p_callback callback, int nb_part_seen)
  48 {
  49     int status = 0;
  50     /* The ebr is located at the first sector of the extended partition */
  51     char *ebr = malloc(SECTOR * sizeof(char));
  52
  53     if (read_sectors(drive_info, ebr, partition_offset + ebr_offset, 1) == -1)
  54         goto abort;
  55
  56     /* Check msdos magic signature */
  57     if (!msdos_magic_present(ebr))
  58         goto abort;
  59
  60     struct part_entry *ptab =
  61         (struct part_entry *)(ebr + PARTITION_TABLES_OFFSET);
  62
  63     for (int i = 0; i < 4; i++) {
  64         if (status == -1)
  65             goto abort;
  66
  67         if (!is_extended_partition(&ptab[i])) {
  68             /*
  69              * This EBR partition table entry points to the
  70              * logical partition associated to that EBR
  71              */
  72             int logical_partition_start = ebr_offset + ptab[i].start_lba;
  73
  74             /* Last EBR in the extended partition? */
  75             if (!logical_partition_start)
  76                 continue;
  77
  78             /*
  79              * Check for garbage:
  80              * 3rd and 4th entries in an EBR should be zero
  81              * Some (malformed) partitioning software still add some
  82              * data partitions there.
  83              */
  84             if (ptab[i].start_lba <= 0 || ptab[i].length <= 0)
  85                 continue;
  86
  87             nb_part_seen++;
  88             callback(drive_info,
  89                      &ptab[i],
  90                      partition_offset + logical_partition_start, nb_part_seen);
  91         } else
  92             status = process_extended_partition(drive_info,
  93                                                 partition_offset,
  94                                                 ptab[i].start_lba,
  95                                                 callback, nb_part_seen);
  96     }
  97
  98     free(ebr);
  99     return 0;
 100
 101 abort:
 102     free(ebr);
 103     return -1;
 104 }
 105
 106 /**
 107  * process_mbr - execute a callback for each partition contained in an {m,e}br
 108  * @drive_info: driveinfo struct describing the drive
 109  * @ptab:       Pointer to the partition table
 110  * @callback:   Callback to execute
 111  **/
 112 static int process_mbr(struct driveinfo *drive_info, struct part_entry *ptab,
 113                        p_callback callback)
 114 {
 115     int status = 0;
 116
 117     for (int i = 0; i < 4; i++) {
 118         if (status == -1)
 119             return -1;
 120
 121         if (ptab[i].start_sect > 0) {
 122             if (is_extended_partition(&ptab[i])) {
 123                 callback(drive_info, &ptab[i], ptab[i].start_lba, i + 1);
 124                 status =
 125                     process_extended_partition(drive_info, ptab[i].start_lba, 0,
 126                                                callback, 4);
 127             } else
 128                 callback(drive_info, &ptab[i], ptab[i].start_lba, i + 1);
 129         }
 130     }
 131
 132     return 0;
 133 }
 134
 135 /**
 136  * parse_partition_table - execute a callback for each partition entry
 137  * @d:          driveinfo struct describing the drive
 138  * @callback:   Callback to execute
 139  *
 140  * The signature of the callback should be the following:
 141  *
 142  * void callback(struct driveinfo *drive_info,
 143  *               struct part_entry *ptab,
 144  *               int offset_root,
 145  *               int nb_part_seen)
 146  **/
 147 int parse_partition_table(struct driveinfo *d, p_callback callback)
 148 {
 149     char *mbr = malloc(SECTOR * sizeof(char));
 150
 151     if (read_mbr(d->disk, mbr) == -1)
 152         return -1;
 153     else {
 154         /* Check msdos magic signature */
 155         if (!msdos_magic_present(mbr))
 156             return -1;
 157
 158         struct part_entry *ptab =
 159             (struct part_entry *)(mbr + PARTITION_TABLES_OFFSET);
 160         return process_mbr(d, ptab, callback);
 161     }
 162 }