com32/gpllib/disk/read.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 <com32.h>
  16 #include <stdlib.h>
  17 #include <string.h>
  18
  19 #include <disk/errno_disk.h>
  20 #include <disk/geom.h>
  21 #include <disk/read.h>
  22 #include <disk/util.h>
  23 #include <disk/common.h>
  24
  25 /*
  26  * TODO: implement file descriptors to cache metadata (geometry, ...)
  27  */
  28
  29 /**
  30  * read_mbr - return a pointer to a malloced buffer containing the mbr
  31  * @drive:      Drive number
  32  * @buf:        Pre-allocated buffer for output
  33  *
  34  * Return the number of sectors read on success or -1 on failure.
  35  * errno_disk contains the error number.
  36  **/
  37 int read_mbr(int drive, void *buf)
  38 {
  39     struct driveinfo drive_info;
  40     drive_info.disk = drive;
  41
  42     /* MBR: lba = 0, 1 sector */
  43     return read_sectors(&drive_info, buf, 0, 1);
  44 }
  45
  46 /**
  47  * dev_read - read from a drive
  48  * @drive:      Drive number
  49  * @buf:        Pre-allocated buffer for output
  50  * @lba:        Position to start reading from
  51  * @sectors:    Number of sectors to read
  52  *
  53  * High-level routine to read from a hard drive.
  54  * Return the number of sectors read on success or -1 on failure.
  55  * errno_disk contains the error number.
  56  **/
  57 int dev_read(int drive, void *buf, unsigned int lba, int sectors)
  58 {
  59     struct driveinfo drive_info;
  60     drive_info.disk = drive;
  61
  62     return read_sectors(&drive_info, buf, lba, sectors);
  63 }
  64
  65 /**
  66  * read_sectors - read several sectors from disk
  67  * @drive_info:         driveinfo struct describing the disk
  68  * @data:               Pre-allocated buffer for output
  69  * @lba:                Position to read
  70  * @sectors:            Number of sectors to read
  71  *
  72  * Return the number of sectors read on success or -1 on failure.
  73  * errno_disk contains the error number.
  74  **/
  75 int read_sectors(struct driveinfo *drive_info, void *data,
  76                  const unsigned int lba, const int sectors)
  77 {
  78     com32sys_t inreg, outreg;
  79     struct ebios_dapa *dapa = __com32.cs_bounce;
  80     void *buf = (char *)__com32.cs_bounce + sectors * SECTOR;
  81     char *bufp = data;
  82
  83     if (get_drive_parameters(drive_info) == -1)
  84         return -1;
  85
  86     memset(&inreg, 0, sizeof inreg);
  87
  88     if (drive_info->ebios) {
  89         dapa->len = sizeof(*dapa);
  90         dapa->count = sectors;
  91         dapa->off = OFFS(buf);
  92         dapa->seg = SEG(buf);
  93         dapa->lba = lba;
  94
  95         inreg.esi.w[0] = OFFS(dapa);
  96         inreg.ds = SEG(dapa);
  97         inreg.edx.b[0] = drive_info->disk;
  98         inreg.eax.b[1] = 0x42;  /* Extended read */
  99     } else {
 100         unsigned int c, h, s;
 101
 102         if (!drive_info->cbios) {       // XXX errno
 103             /* We failed to get the geometry */
 104             if (lba)
 105                 return -1;      /* Can only read MBR */
 106
 107             s = 1;
 108             h = 0;
 109             c = 0;
 110         } else
 111             lba_to_chs(drive_info, lba, &s, &h, &c);
 112
 113         // XXX errno
 114         if (s > 63 || h > 256 || c > 1023)
 115             return -1;
 116
 117         inreg.eax.w[0] = 0x0201;        /* Read one sector */
 118         inreg.ecx.b[1] = c & 0xff;
 119         inreg.ecx.b[0] = s + (c >> 6);
 120         inreg.edx.b[1] = h;
 121         inreg.edx.b[0] = drive_info->disk;
 122         inreg.ebx.w[0] = OFFS(buf);
 123         inreg.es = SEG(buf);
 124     }
 125
 126     /* Perform the read */
 127     if (int13_retry(&inreg, &outreg)) {
 128         errno_disk = outreg.eax.b[1];
 129         return -1;              /* Give up */
 130     }
 131
 132     memcpy(bufp, buf, sectors * SECTOR);
 133
 134     return sectors;
 135 }