初始化文件系统并装载 文件系统根据启动时的根目录和文件结构进行初始化操作。 typedef struct { int magic; /* id to tell the type of filesystem */ int fileAllocationOffset; /* where is the file allocation table */ int fileAllocationLength; /* length of allocation table */ int rootDirectoryOffset; /* offset in sectors of root directory */ int rootDirectoryCount; /* number of items in the directory */ short setupStart; /* first sector of secondary loader */ short setupSize; /* size in sectors of secondary loader */ short kernelStart; /* first sector of kernel to run */ short kernelSize; /* size in sectors of kernel to run */ } bootSector; typedef struct { char fileName[8+4]; /* at