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package resize_fat::boot_sector; # $Id: boot_sector.pm 210307 2004-12-13 15:56:00Z tvignaud $
use diagnostics;
use strict;
use common;
use resize_fat::io;
use resize_fat::any;
use resize_fat::directory;
#- Oops, this will be unresizable on big-endian machine. trapped by signature.
my $format = "a3 a8 S C S C S S C S S S I I I S S I S S a458 S";
my @fields = (
'boot_jump', #- boot strap short or near jump
'system_id', #- Name - can be used to special case partition manager volumes
'sector_size', #- bytes per logical sector
'cluster_size_in_sectors', #- sectors/cluster
'nb_reserved', #- reserved sectors
'nb_fats', #- number of FATs
'nb_root_dir_entries', #- number of root directory entries
'small_nb_sectors', #- number of sectors: big_nb_sectors supersedes
'media', #- media code
'fat16_fat_length', #- sectors/FAT for FAT12/16
'sectors_per_track',
'nb_heads',
'nb_hidden', #- (unused)
'big_nb_sectors', #- number of sectors (if small_nb_sectors == 0)
#- FAT32-only entries
'fat32_fat_length', #- size of FAT in sectors
'fat32_flags', #- bit8: fat mirroring,
#- low4: active fat
'fat32_version', #- minor * 256 + major
'fat32_root_dir_cluster',
'info_offset_in_sectors',
'fat32_backup_sector',
#- Common again...
'boot_code', #- Boot code (or message)
'boot_sign', #- 0xAA55
);
1;
#- trimfs_init_boot_sector() - reads in the boot sector - gets important info out
#- of boot sector, and puts in main structure - performs sanity checks - returns 1
#- on success, 0 on failureparameters: filesystem an empty structure to fill.
sub read($) {
my ($fs) = @_;
my $boot = eval { resize_fat::io::read($fs, 0, $SECTORSIZE) }; $@ and die "reading boot sector failed on device $fs->{fs_name}";
@$fs{@fields} = unpack $format, $boot;
$fs->{nb_sectors} = $fs->{small_nb_sectors} || $fs->{big_nb_sectors};
$fs->{cluster_size} = $fs->{cluster_size_in_sectors} * $fs->{sector_size};
$fs->{boot_sign} == 0xAA55 or die "Invalid signature for a MS-based filesystem.\n";
$fs->{nb_sectors} < 32 and die "Too few sectors for viable file system\n";
$fs->{nb_fats} == 2 or cdie "Weird number of FATs: $fs->{nb_fats}, not 2.\n";
$fs->{sector_size} == 512 or cdie "Strange sector_size != 512\n";
if ($fs->{fat16_fat_length}) {
#- asserting FAT16, will be verified later on
$resize_fat::isFAT32 = 0;
$fs->{fs_type} = 'FAT16';
$fs->{fs_type_size} = 16;
$fs->{fat_length} = $fs->{fat16_fat_length};
$resize_fat::bad_cluster_value = 0xfff7; #- 2**16 - 1
} else {
$resize_fat::isFAT32 = 1;
$fs->{fs_type} = 'FAT32';
$fs->{fs_type_size} = 32;
$fs->{fat_length} = $fs->{fat32_fat_length};
$fs->{nb_root_dir_entries} = 0;
$fs->{info_offset} = $fs->{info_offset_in_sectors} * $fs->{sector_size};
$resize_fat::bad_cluster_value = 0x0ffffff7;
}
$fs->{fat_offset} = $fs->{nb_reserved} * $fs->{sector_size};
$fs->{fat_size} = $fs->{fat_length} * $fs->{sector_size};
$fs->{root_dir_offset} = $fs->{fat_offset} + $fs->{fat_size} * $fs->{nb_fats};
$fs->{root_dir_size} = $fs->{nb_root_dir_entries} * resize_fat::directory::entry_size();
$fs->{cluster_offset} = $fs->{root_dir_offset} + $fs->{root_dir_size} - 2 * $fs->{cluster_size};
$fs->{nb_fat_entries} = divide($fs->{fat_size}, $fs->{fs_type_size} / 8);
#- - 2 because clusters 0 & 1 does not exist
$fs->{nb_clusters} = divide($fs->{nb_sectors} * $fs->{sector_size} - $fs->{cluster_offset}, $fs->{cluster_size}) - 2;
$fs->{dir_entries_per_cluster} = divide($fs->{cluster_size}, psizeof($format));
#- $fs->{nb_clusters} >= resize_fat::any::min_cluster_count($fs) or die "error: not enough sectors for a $fs->{fs_type}\n";
$fs->{nb_clusters} < resize_fat::any::max_cluster_count($fs) or die "error: too many sectors for a $fs->{fs_type}\n";
}
sub write($) {
my ($fs) = @_;
my $boot = pack($format, @$fs{@fields});
eval { resize_fat::io::write($fs, 0, $SECTORSIZE, $boot) }; $@ and die "writing the boot sector failed on device $fs->{fs_name}";
if ($resize_fat::isFAT32) {
#- write backup
eval { resize_fat::io::write($fs, $fs->{fat32_backup_sector} * $SECTORSIZE, $SECTORSIZE, $boot) };
$@ and die "writing the backup boot sector (#$fs->{fat32_backup_sector}) failed on device $fs->{fs_name}";
}
}
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