// $Id: ex3b.c,v 1.3 2006/12/21 01:14:35 kaiya Exp kaiya $

/*
Spec
   Get dirent data in n'th block from standard input
Usage
   ./a.out block_number < filesystem_file
Output
	List of information of each file in the directory
Limit
   block_number: natural number and it should specify directory block. 
   0<=block_number<1440
   filesytem_file should be simple ext2 file system dump; 
   i.e. block size=1024B, number of blocks=1440.
Compile
   gcc thisfile.c using ext2_os2006.h
Platform
	gcc in PPC
 */

#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

// #include <linux/ext2_fs.h>
#include "ext2_os2006.h"

// 1024*1440 = 1474560
#define ALLBLOCKSIZE 1474560
#define BLOCKSIZE 1024
#define BLOCKNUMBER 1440

// data in all blocks are stored here.
unsigned char blocks[ALLBLOCKSIZE];

/*
 Get the beginning of n'th block.
 Argument:
   n ro: specify the number of block. (0, 1, 2, ...)
 Return:
   pointer to the beginning of the block. 
   NULL if fail.
 */
unsigned char* nth_block(int n){
	if(n<0 || BLOCKNUMBER<=n) return NULL; // out of range
	return blocks+(n*BLOCKSIZE);
}

/*
 Get dir_entry from byte array. 
 Arguments:
   *block ro: begin of byte array
   *de rw: begin address of gotten dir_entry. de->name is terminated.
   *resta rw: number of bytes still remained. 
 Return:
   pointer to the next dir entry.
   NULL if fail.
 */
unsigned char* get_dir_entry(
	struct ext2_dir_entry_2* de, unsigned char* block, int* resta
){
	if(*resta<=0) return NULL;
	memcpy(de, block, sizeof(*de));
	de->name[de->name_len]='\0';
	*resta -= (int)rev16(de->rec_len);
	return block+(int)rev16(de->rec_len);
}

main(int argc, char* argv[]){
int nb;
unsigned char* blockptr;
struct ext2_dir_entry_2 dirent2;
int rest=BLOCKSIZE;

	// check argument
	if(argc<2) exit(1);
	nb=atoi(argv[1]);
	if(nb<0 || nb>1440) exit(2);

	// load all blocks in the file system.
	if(read(0, blocks, ALLBLOCKSIZE)!=ALLBLOCKSIZE){
		fprintf(stderr, "Can not read all blocks!\n");
		exit(1);
	}
	// seek a block.
	if((blockptr=nth_block(nb))==NULL){
		fprintf(stderr, "Block number overrun!\n");
		exit(3);
	}

	// parse the block.
	while((blockptr=get_dir_entry(&dirent2, blockptr, &rest))!=NULL){
		printf("inode = %d, file type = %d, file name =(%s)\n",
			rev32(dirent2.inode), dirent2.file_type, dirent2.name
		);
	}
}