path: root/src/boot.c

/* boot.c - Read and analyze ia PC/MS-DOS boot sector

   Copyright (C) 1993 Werner Almesberger <werner.almesberger@lrc.di.epfl.ch>
   Copyright (C) 1998 Roman Hodek <Roman.Hodek@informatik.uni-erlangen.de>

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program. If not, see <http://www.gnu.org/licenses/>.

   On Debian systems, the complete text of the GNU General Public License
   can be found in /usr/share/common-licenses/GPL-3 file.
*/

/* 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 <stdlib.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 */

/* cut-over cluster counts for FAT12 and FAT16 */
#define FAT12_THRESHOLD  4085
#define FAT16_THRESHOLD 65525

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__ || defined __arm__
/* 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 *)&__v );	\
    })
#else
#define GET_UNALIGNED_W(f) CF_LE_W( *(unsigned short *)&f )
#endif


static char *get_media_descr( unsigned char media )
{
    unsigned 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",
	   (unsigned long long)fs->fat_start,
	   (unsigned long long)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",
	       (unsigned long long)fs->root_start,
	       (unsigned long long)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",
	   (unsigned long long)fs->data_start,
	   (unsigned long long)fs->data_start/lss);
    printf("%10lu data clusters (%llu bytes)\n",fs->clusters,
	   (unsigned long long)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((loff_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((loff_t)s*lss,sizeof(i),&i);
		b->info_sector = CT_LE_W(s);
		fs_write((loff_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",
		    (unsigned long long)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",
		    (unsigned long long)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",
		    (unsigned long long)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 = (loff_t)CF_LE_W(b.reserved)*logical_sector_size;
    fs->root_start = ((loff_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" );
	if (fs->clusters < FAT16_THRESHOLD)
		printf("Warning: Filesystem is FAT32 according to fat_length "
			"and fat32_length fields,\n"
			"  but has only %lu clusters, less than the required "
			"minimum of %d.\n"
			"  This may lead to problems on some systems.\n",
			fs->clusters, FAT16_THRESHOLD);

	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 >= FAT12_THRESHOLD) ? 16 : 12;
	if (fs->clusters >= FAT16_THRESHOLD)
		die("Too many clusters (%lu) for FAT16 filesystem.",
			fs->clusters);
    }
    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;

    fs->label = calloc(12, sizeof (__u8));
    if (fs->fat_bits == 12 || fs->fat_bits == 16) {
        struct boot_sector_16 *b16 = (struct boot_sector_16 *)&b;
        if (b16->extended_sig == 0x29)
            memmove(fs->label, b16->label, 11);
        else
            fs->label = NULL;
    } else if (fs->fat_bits == 32) {
        if (b.extended_sig == 0x29)
            memmove(fs->label, &b.label, 11);
        else
            fs->label = NULL;
    }

    if (fs->clusters > ((unsigned long long)fs->fat_size*8/fs->fat_bits)-2)
	die("File system has %d clusters but only space for %d FAT entries.",
	  fs->clusters,((unsigned long long)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);
#if 0 /* linux kernel doesn't check that either */
    /* ++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.");
#endif
    if (verbose) dump_boot(fs,&b,logical_sector_size);
}

void write_label(DOS_FS *fs, char *label)
{
    struct boot_sector b;
    struct boot_sector_16 *b16 = (struct boot_sector_16 *)&b;
    int l = strlen(label);

    while (l < 11)
        label[l++] = ' ';

    fs_read(0, sizeof(b), &b);
    if (fs->fat_bits == 12 || fs->fat_bits == 16) {
        if (b16->extended_sig != 0x29) {
            b16->extended_sig = 0x29;
            b16->serial = 0;
            memmove(b16->fs_type, fs->fat_bits == 12 ?"FAT12   ":"FAT16   ", 8);
        }
        memmove(b16->label, label, 11);
    } else if (fs->fat_bits == 32) {
        if (b.extended_sig != 0x29) {
            b.extended_sig = 0x29;
            b.serial = 0;
            memmove(b.fs_type, "FAT32   ", 8);
        }
        memmove(b.label, label, 11);
    }
    fs_write(0, sizeof(b), &b);
    if (fs->fat_bits == 32 && fs->backupboot_start)
        fs_write(fs->backupboot_start, sizeof(b), &b);
}

/* Local Variables: */
/* tab-width: 8     */
/* End:             */