mkfs.fat: Add support for autodetecting FAT type based on file size

Userland/Utilities/mkfs.fat.cpp

@@ -570,29 +570,69 @@ static ErrorOr<void> format_fat32(Core::File& file, u64 file_size, u32 volume_id
  return {};
 }
 
+static ErrorOr<int> detect_fat_type_from_file_size(u64 file_size)
+{
+ u32 sector_count = file_size / 512;
+
+ auto check_table_for_support = [sector_count](auto const& table, bool fat12 = false) {
+ for (auto const& potential_entry : table) {
+ if (fat12 && sector_count == potential_entry.disk_size)
+ return true;
+ else if (!fat12 && sector_count <= potential_entry.disk_size)
+ return potential_entry.sectors_per_cluster != 0;
+ }
+ return false;
+ };
+
+ if (check_table_for_support(s_disk_table_fat12, true))
+ return 12;
+
+ if (file_size < 512 * MiB && check_table_for_support(s_disk_table_fat16))
+ return 16;
+
+ if (check_table_for_support(s_disk_table_fat32))
+ return 32;
+
+ return Error::from_string_literal("Unable to autodetect a compatible FAT variant");
+}
+
+static bool is_valid_fat_type(int fat_type)
+{
+ return fat_type == 12 || fat_type == 16 || fat_type == 32;
+}
+
 ErrorOr<int> serenity_main(Main::Arguments arguments)
 {
  StringView file_path;
- int fat_type = 0;
+ Optional<int> fat_type_or_empty;
 
  struct timeval time;
  gettimeofday(&time, NULL);
  u32 volume_id = static_cast<u32>(time.tv_sec) | static_cast<u32>(time.tv_usec);
 
  Core::ArgsParser args_parser;
- args_parser.add_option(fat_type, "FAT type to use, valid types are 12, 16, and 32", "FAT-type", 'F', "FAT type");
+ args_parser.add_option(fat_type_or_empty, "FAT type to use, valid types are 12, 16, and 32", "FAT-type", 'F', "FAT type");
  args_parser.add_positional_argument(file_path, "File to format", "file", Core::ArgsParser::Required::Yes);
  args_parser.parse(arguments);
 
  auto file = TRY(Core::File::open(file_path, Core::File::OpenMode::ReadWrite | Core::File::OpenMode::DontCreate));
 
  u64 file_size = 0;
-
  if (FileSystem::is_device(file->fd()))
  file_size = TRY(FileSystem::block_device_size_from_ioctl(file->fd()));
  else
  file_size = TRY(FileSystem::size_from_fstat(file->fd()));
 
+ int fat_type = 0;
+ if (fat_type_or_empty.has_value()) {
+ fat_type = fat_type_or_empty.release_value();
+
+ if (!is_valid_fat_type(fat_type))
+ return Error::from_string_literal("Invalid FAT type specified, valid types are 12, 16, and 32");
+ } else {
+ fat_type = TRY(detect_fat_type_from_file_size(file_size));
+ }
+
  switch (fat_type) {
  case 12:
  TRY(format_fat_16_bit(*file, FATType::FAT12, file_size, volume_id));
@@ -604,7 +644,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
  TRY(format_fat32(*file, file_size, volume_id));
  break;
  default:
- return Error::from_string_literal("Invalid or no FAT type specified, valid types are 12, 16, and 32");
+ VERIFY_NOT_REACHED();
  }
 
  sync();