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 filesystem\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}"; } }