📄 boot.c
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/* boot.c - Read and analyze ia PC/MS-DOS boot sector */
/* Written 1993 by Werner Almesberger */
/* FAT32, VFAT, Atari format support, and various fixes additions May 1998
* by Roman Hodek <Roman.Hodek@informatik.uni-erlangen.de> */
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include "common.h"
#include "dosfsck.h"
#include "io.h"
#include "boot.h"
#define ROUND_TO_MULTIPLE(n,m) ((n) && (m) ? (n)+(m)-1-((n)-1)%(m) : 0)
/* don't divide by zero */
static struct {
__u8 media;
char *descr;
} mediabytes[] = {
{ 0xf0, "5.25\" or 3.5\" HD floppy" },
{ 0xf8, "hard disk" },
{ 0xf9, "3,5\" 720k floppy 2s/80tr/9sec or "
"5.25\" 1.2M floppy 2s/80tr/15sec" },
{ 0xfa, "5.25\" 320k floppy 1s/80tr/8sec" },
{ 0xfb, "3.5\" 640k floppy 2s/80tr/8sec" },
{ 0xfc, "5.25\" 180k floppy 1s/40tr/9sec" },
{ 0xfd, "5.25\" 360k floppy 2s/40tr/9sec" },
{ 0xfe, "5.25\" 160k floppy 1s/40tr/8sec" },
{ 0xff, "5.25\" 320k floppy 2s/40tr/8sec" },
};
#if defined __alpha || defined __ia64__ || defined __s390x__ || defined __x86_64__ || defined __ppc64__
/* Unaligned fields must first be copied byte-wise */
#define GET_UNALIGNED_W(f) \
({ \
unsigned short __v; \
memcpy( &__v, &f, sizeof(__v) ); \
CF_LE_W( *(unsigned short *)&f ); \
})
#else
#define GET_UNALIGNED_W(f) CF_LE_W( *(unsigned short *)&f )
#endif
static char *get_media_descr( unsigned char media )
{
int i;
for( i = 0; i < sizeof(mediabytes)/sizeof(*mediabytes); ++i ) {
if (mediabytes[i].media == media)
return( mediabytes[i].descr );
}
return( "undefined" );
}
static void dump_boot(DOS_FS *fs,struct boot_sector *b,unsigned lss)
{
unsigned short sectors;
printf("Boot sector contents:\n");
if (!atari_format) {
char id[9];
strncpy(id,b->system_id,8);
id[8] = 0;
printf("System ID \"%s\"\n",id);
}
else {
/* On Atari, a 24 bit serial number is stored at offset 8 of the boot
* sector */
printf("Serial number 0x%x\n",
b->system_id[5] | (b->system_id[6]<<8) | (b->system_id[7]<<16));
}
printf("Media byte 0x%02x (%s)\n",b->media,get_media_descr(b->media));
printf("%10d bytes per logical sector\n",GET_UNALIGNED_W(b->sector_size));
printf("%10d bytes per cluster\n",fs->cluster_size);
printf("%10d reserved sector%s\n",CF_LE_W(b->reserved),
CF_LE_W(b->reserved) == 1 ? "" : "s");
printf("First FAT starts at byte %llu (sector %llu)\n",
(__u64)fs->fat_start,
(__u64)fs->fat_start/lss);
printf("%10d FATs, %d bit entries\n",b->fats,fs->fat_bits);
printf("%10d bytes per FAT (= %u sectors)\n",fs->fat_size,
fs->fat_size/lss);
if (!fs->root_cluster) {
printf("Root directory starts at byte %llu (sector %llu)\n",
(__u64)fs->root_start,
(__u64)fs->root_start/lss);
printf("%10d root directory entries\n",fs->root_entries);
}
else {
printf( "Root directory start at cluster %lu (arbitrary size)\n",
fs->root_cluster);
}
printf("Data area starts at byte %llu (sector %llu)\n",
(__u64)fs->data_start,
(__u64)fs->data_start/lss);
printf("%10lu data clusters (%llu bytes)\n",fs->clusters,
(__u64)fs->clusters*fs->cluster_size);
printf("%u sectors/track, %u heads\n",CF_LE_W(b->secs_track),
CF_LE_W(b->heads));
printf("%10u hidden sectors\n",
atari_format ?
/* On Atari, the hidden field is only 16 bit wide and unused */
(((unsigned char *)&b->hidden)[0] |
((unsigned char *)&b->hidden)[1] << 8) :
CF_LE_L(b->hidden));
sectors = GET_UNALIGNED_W( b->sectors );
printf("%10u sectors total\n", sectors ? sectors : CF_LE_L(b->total_sect));
}
static void check_backup_boot(DOS_FS *fs, struct boot_sector *b, int lss)
{
struct boot_sector b2;
if (!fs->backupboot_start) {
printf( "There is no backup boot sector.\n" );
if (CF_LE_W(b->reserved) < 3) {
printf( "And there is no space for creating one!\n" );
return;
}
if (interactive)
printf( "1) Create one\n2) Do without a backup\n" );
else printf( " Auto-creating backup boot block.\n" );
if (!interactive || get_key("12","?") == '1') {
int bbs;
/* The usual place for the backup boot sector is sector 6. Choose
* that or the last reserved sector. */
if (CF_LE_W(b->reserved) >= 7 && CF_LE_W(b->info_sector) != 6)
bbs = 6;
else {
bbs = CF_LE_W(b->reserved) - 1;
if (bbs == CF_LE_W(b->info_sector))
--bbs; /* this is never 0, as we checked reserved >= 3! */
}
fs->backupboot_start = bbs*lss;
b->backup_boot = CT_LE_W(bbs);
fs_write(fs->backupboot_start,sizeof(*b),b);
fs_write((off_t)offsetof(struct boot_sector,backup_boot),
sizeof(b->backup_boot),&b->backup_boot);
printf( "Created backup of boot sector in sector %d\n", bbs );
return;
}
else return;
}
fs_read(fs->backupboot_start,sizeof(b2),&b2);
if (memcmp(b,&b2,sizeof(b2)) != 0) {
/* there are any differences */
__u8 *p, *q;
int i, pos, first = 1;
char buf[20];
printf( "There are differences between boot sector and its backup.\n" );
printf( "Differences: (offset:original/backup)\n " );
pos = 2;
for( p = (__u8 *)b, q = (__u8 *)&b2, i = 0; i < sizeof(b2);
++p, ++q, ++i ) {
if (*p != *q) {
sprintf( buf, "%s%u:%02x/%02x", first ? "" : ", ",
(unsigned)(p-(__u8 *)b), *p, *q );
if (pos + strlen(buf) > 78) printf( "\n " ), pos = 2;
printf( "%s", buf );
pos += strlen(buf);
first = 0;
}
}
printf( "\n" );
if (interactive)
printf( "1) Copy original to backup\n"
"2) Copy backup to original\n"
"3) No action\n" );
else printf( " Not automatically fixing this.\n" );
switch (interactive ? get_key("123","?") : '3') {
case '1':
fs_write(fs->backupboot_start,sizeof(*b),b);
break;
case '2':
fs_write(0,sizeof(b2),&b2);
break;
default:
break;
}
}
}
static void init_fsinfo(struct info_sector *i)
{
i->magic = CT_LE_L(0x41615252);
i->signature = CT_LE_L(0x61417272);
i->free_clusters = CT_LE_L(-1);
i->next_cluster = CT_LE_L(2);
i->boot_sign = CT_LE_W(0xaa55);
}
static void read_fsinfo(DOS_FS *fs, struct boot_sector *b,int lss)
{
struct info_sector i;
if (!b->info_sector) {
printf( "No FSINFO sector\n" );
if (interactive)
printf( "1) Create one\n2) Do without FSINFO\n" );
else printf( " Not automatically creating it.\n" );
if (interactive && get_key("12","?") == '1') {
/* search for a free reserved sector (not boot sector and not
* backup boot sector) */
__u32 s;
for( s = 1; s < CF_LE_W(b->reserved); ++s )
if (s != CF_LE_W(b->backup_boot)) break;
if (s > 0 && s < CF_LE_W(b->reserved)) {
init_fsinfo(&i);
fs_write((off_t)s*lss,sizeof(i),&i);
b->info_sector = CT_LE_W(s);
fs_write((off_t)offsetof(struct boot_sector,info_sector),
sizeof(b->info_sector),&b->info_sector);
if (fs->backupboot_start)
fs_write(fs->backupboot_start+
offsetof(struct boot_sector,info_sector),
sizeof(b->info_sector),&b->info_sector);
}
else {
printf( "No free reserved sector found -- "
"no space for FSINFO sector!\n" );
return;
}
}
else return;
}
fs->fsinfo_start = CF_LE_W(b->info_sector)*lss;
fs_read(fs->fsinfo_start,sizeof(i),&i);
if (i.magic != CT_LE_L(0x41615252) ||
i.signature != CT_LE_L(0x61417272) ||
i.boot_sign != CT_LE_W(0xaa55)) {
printf( "FSINFO sector has bad magic number(s):\n" );
if (i.magic != CT_LE_L(0x41615252))
printf( " Offset %llu: 0x%08x != expected 0x%08x\n",
(__u64)offsetof(struct info_sector,magic),
CF_LE_L(i.magic),0x41615252);
if (i.signature != CT_LE_L(0x61417272))
printf( " Offset %llu: 0x%08x != expected 0x%08x\n",
(__u64)offsetof(struct info_sector,signature),
CF_LE_L(i.signature),0x61417272);
if (i.boot_sign != CT_LE_W(0xaa55))
printf( " Offset %llu: 0x%04x != expected 0x%04x\n",
(__u64)offsetof(struct info_sector,boot_sign),
CF_LE_W(i.boot_sign),0xaa55);
if (interactive)
printf( "1) Correct\n2) Don't correct (FSINFO invalid then)\n" );
else printf( " Auto-correcting it.\n" );
if (!interactive || get_key("12","?") == '1') {
init_fsinfo(&i);
fs_write(fs->fsinfo_start,sizeof(i),&i);
}
else fs->fsinfo_start = 0;
}
if (fs->fsinfo_start)
fs->free_clusters = CF_LE_L(i.free_clusters);
}
void read_boot(DOS_FS *fs)
{
struct boot_sector b;
unsigned total_sectors;
unsigned short logical_sector_size, sectors;
unsigned fat_length;
loff_t data_size;
fs_read(0,sizeof(b),&b);
logical_sector_size = GET_UNALIGNED_W(b.sector_size);
if (!logical_sector_size) die("Logical sector size is zero.");
fs->cluster_size = b.cluster_size*logical_sector_size;
if (!fs->cluster_size) die("Cluster size is zero.");
if (b.fats != 2 && b.fats != 1)
die("Currently, only 1 or 2 FATs are supported, not %d.\n",b.fats);
fs->nfats = b.fats;
sectors = GET_UNALIGNED_W(b.sectors);
total_sectors = sectors ? sectors : CF_LE_L(b.total_sect);
if (verbose) printf("Checking we can access the last sector of the filesystem\n");
/* Can't access last odd sector anyway, so round down */
fs_test((loff_t)((total_sectors & ~1)-1)*(loff_t)logical_sector_size,
logical_sector_size);
fat_length = CF_LE_W(b.fat_length) ?
CF_LE_W(b.fat_length) : CF_LE_L(b.fat32_length);
fs->fat_start = (off_t)CF_LE_W(b.reserved)*logical_sector_size;
fs->root_start = ((off_t)CF_LE_W(b.reserved)+b.fats*fat_length)*
logical_sector_size;
fs->root_entries = GET_UNALIGNED_W(b.dir_entries);
fs->data_start = fs->root_start+ROUND_TO_MULTIPLE(fs->root_entries <<
MSDOS_DIR_BITS,logical_sector_size);
data_size = (loff_t)total_sectors*logical_sector_size-fs->data_start;
fs->clusters = data_size/fs->cluster_size;
fs->root_cluster = 0; /* indicates standard, pre-FAT32 root dir */
fs->fsinfo_start = 0; /* no FSINFO structure */
fs->free_clusters = -1; /* unknown */
if (!b.fat_length && b.fat32_length) {
fs->fat_bits = 32;
fs->root_cluster = CF_LE_L(b.root_cluster);
if (!fs->root_cluster && fs->root_entries)
/* M$ hasn't specified this, but it looks reasonable: If
* root_cluster is 0 but there is a separate root dir
* (root_entries != 0), we handle the root dir the old way. Give a
* warning, but convertig to a root dir in a cluster chain seems
* to complex for now... */
printf( "Warning: FAT32 root dir not in cluster chain! "
"Compability mode...\n" );
else if (!fs->root_cluster && !fs->root_entries)
die("No root directory!");
else if (fs->root_cluster && fs->root_entries)
printf( "Warning: FAT32 root dir is in a cluster chain, but "
"a separate root dir\n"
" area is defined. Cannot fix this easily.\n" );
fs->backupboot_start = CF_LE_W(b.backup_boot)*logical_sector_size;
check_backup_boot(fs,&b,logical_sector_size);
read_fsinfo(fs,&b,logical_sector_size);
}
else if (!atari_format) {
/* On real MS-DOS, a 16 bit FAT is used whenever there would be too
* much clusers otherwise. */
fs->fat_bits = (fs->clusters > MSDOS_FAT12) ? 16 : 12;
}
else {
/* On Atari, things are more difficult: GEMDOS always uses 12bit FATs
* on floppies, and always 16 bit on harddisks. */
fs->fat_bits = 16; /* assume 16 bit FAT for now */
/* If more clusters than fat entries in 16-bit fat, we assume
* it's a real MSDOS FS with 12-bit fat. */
if (fs->clusters+2 > fat_length*logical_sector_size*8/16 ||
/* if it's a floppy disk --> 12bit fat */
device_no == 2 ||
/* if it's a ramdisk or loopback device and has one of the usual
* floppy sizes -> 12bit FAT */
((device_no == 1 || device_no == 7) &&
(total_sectors == 720 || total_sectors == 1440 ||
total_sectors == 2880)))
fs->fat_bits = 12;
}
/* On FAT32, the high 4 bits of a FAT entry are reserved */
fs->eff_fat_bits = (fs->fat_bits == 32) ? 28 : fs->fat_bits;
fs->fat_size = fat_length*logical_sector_size;
if (fs->clusters > ((__u64)fs->fat_size*8/fs->fat_bits)-2)
die("File system has %d clusters but only space for %d FAT entries.",
fs->clusters,((__u64)fs->fat_size*8/fs->fat_bits)-2);
if (!fs->root_entries && !fs->root_cluster)
die("Root directory has zero size.");
if (fs->root_entries & (MSDOS_DPS-1))
die("Root directory (%d entries) doesn't span an integral number of "
"sectors.",fs->root_entries);
if (logical_sector_size & (SECTOR_SIZE-1))
die("Logical sector size (%d bytes) is not a multiple of the physical "
"sector size.",logical_sector_size);
/* ++roman: On Atari, these two fields are often left uninitialized */
if (!atari_format && (!b.secs_track || !b.heads))
die("Invalid disk format in boot sector.");
if (verbose) dump_boot(fs,&b,logical_sector_size);
}
/* Local Variables: */
/* tab-width: 8 */
/* End: */
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