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fat16: Correct offset of FAT region and make getter for region offsets

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This commit is contained in:
pent0 2019-10-11 06:42:42 +07:00
parent eb17225960
commit fd12d20bb3
2 changed files with 23 additions and 10 deletions
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4
include/fat16/fat16.h
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@ -29,6 +29,10 @@ namespace Fat16 {
char file_sys_id[8];
std::uint8_t bootstrap_code[0x1C0];
std::uint16_t boot_block_sig;
std::uint32_t fat_region_start() const;
std::uint32_t root_directory_region_start() const;
std::uint32_t data_region_start() const;
};
#pragma pack(pop)

29
src/fat16.cpp
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@ -5,6 +5,20 @@
#include <algorithm>
namespace Fat16 {
// https://www.win.tue.nl/~aeb/linux/fs/fat/fat-1.html
// reserved blocks -> fat -> root directory -> data area
std::uint32_t BootBlock::fat_region_start() const {
return num_reserved_blocks * bytes_per_block;
}
std::uint32_t BootBlock::root_directory_region_start() const {
return fat_region_start() + (num_fat * num_blocks_per_fat) * bytes_per_block;
}
std::uint32_t BootBlock::data_region_start() const {
return root_directory_region_start() + (num_root_dirs * sizeof(FundamentalEntry));
}
std::string FundamentalEntry::get_filename() {
EntryType etype = get_entry_type_from_filename();
std::string fname(reinterpret_cast<char*>(filename));
@ -49,13 +63,13 @@ namespace Fat16 {
const std::uint32_t current = get_current_image_offset();
// Seek to beginning of the FAT
seek_func(userdata, boot_block.bytes_per_block, IMAGE_SEEK_MODE_BEG);
seek_func(userdata, boot_block.fat_region_start() + (target * 2), IMAGE_SEEK_MODE_BEG);
ClusterID next = 0;
if (read_func(userdata, &next, sizeof(ClusterID)) != sizeof(ClusterID)) {
return 0;
}
seek_func(userdata, current, IMAGE_SEEK_MODE_BEG);
return next;
}
@ -85,14 +99,9 @@ namespace Fat16 {
}
// Add the FAT with the boot block, then add the root directory entries size
offset_start_data_area = boot_block.bytes_per_block * (boot_block.num_blocks_per_fat * boot_block.num_fat + 1);
offset_start_data_area += ((sizeof(FundamentalEntry) * boot_block.num_root_dirs + boot_block.bytes_per_block - 1) / boot_block.bytes_per_block)
* boot_block.bytes_per_block;
offset_start_data_area = boot_block.data_region_start();
offset_start_data_area += offset_in_that_cluster;
// TODO: Maybe I miss something? Cause this is unatural, but it makes things work.
offset_start_data_area += boot_block.bytes_per_block;
// Let's seek to that place.
seek_func(userdata, offset_start_data_area, IMAGE_SEEK_MODE_BEG);
@ -125,7 +134,7 @@ namespace Fat16 {
std::uint32_t offset_root_dir = 0;
// Add the FAT with the boot block, then add the root directory entries size
offset_root_dir = boot_block.bytes_per_block * (boot_block.num_blocks_per_fat * boot_block.num_fat + 1);
offset_root_dir = boot_block.root_directory_region_start();
seek_func(userdata, offset_root_dir + entry.cursor_record, IMAGE_SEEK_MODE_BEG);
LongFileNameEntry extended_entry;