inode.c

linux的文件系统的部分代码的详细注释

	unsigned long block_group;
	unsigned long group_desc;
	unsigned long desc;
	unsigned long block;
	unsigned long offset;
	struct ext2_group_desc * gdp;

       /*节点号!=根节点&&节点号<第一个节点号||节点号>总节点计数时，
         *出错则输出错误信息
         */
	if ((inode->i_ino != EXT2_ROOT_INO && inode->i_ino != EXT2_ACL_IDX_INO &&
	     inode->i_ino != EXT2_ACL_DATA_INO &&
	     inode->i_ino < EXT2_FIRST_INO(inode->i_sb)) ||
	    inode->i_ino > le32_to_cpu(inode->i_sb->u.ext2_sb.s_es->s_inodes_count)) {
		ext2_error (inode->i_sb, "ext2_read_inode",
			    "bad inode number: %lu", inode->i_ino);
		goto bad_inode;
	}
	/*该索引节点所在的块组号=索引节点号/每组中所有节点数*/
	block_group = (inode->i_ino - 1) / EXT2_INODES_PER_GROUP(inode->i_sb);
	/*如果索引节点所在的块组号>=文件系统中总块号*/
	if (block_group >= inode->i_sb->u.ext2_sb.s_groups_count) {
		ext2_error (inode->i_sb, "ext2_read_inode",
			    "group >= groups count");
		goto bad_inode;
	}
	/*组描述符在组描述表中的块号=块组号/每块中组描述符数，
	 *每个组描述符是32字节大小，在一个1KB大小的块中可存储32个组描述符，
	 *每个块用一个组描述符表示，
	 *因为组描述符已读入buffer中形成组描述表s_group_desc[]数组，
	 *组描述表是以buffer为数组元素的，
	 *每个buffer大小为一个数据块，
	 *所以需要确定组描述符在组描述表的那一块
	 *以及是该块中的第几组描述符
	 */
	group_desc = block_group >> EXT2_DESC_PER_BLOCK_BITS(inode->i_sb);

	/*组描述符具体是该块中第几个描述符
	 * =组号对每块中组描述符作相与运算
	 */
	desc = block_group & (EXT2_DESC_PER_BLOCK(inode->i_sb) - 1);

	/*通过s_group_desc[]数组找到这个组描述符所在块在高速缓存中的缓冲区首部*/
	bh = inode->i_sb->u.ext2_sb.s_group_desc[group_desc];
	if (!bh) {
		ext2_error (inode->i_sb, "ext2_read_inode",
			    "Descriptor not loaded");
		goto bad_inode;
	}

       /*通过缓冲区首部找到数据区，找到组描述符后，
        *就可以通过组描述符结构中的bg_inode_table
        *找到索引节点表首块在高速缓存中的地址
        */
	gdp = (struct ext2_group_desc *) bh->b_data;
	/*
	 * Figure out the offset within the block group inode table
	 */
	 /*计算该索引节点在块中的偏移位置*/
	offset = ((inode->i_ino - 1) % EXT2_INODES_PER_GROUP(inode->i_sb)) *
		EXT2_INODE_SIZE(inode->i_sb);

	/*计算索引节点所在块的地址，
	 *有了block和offset就可以找到索引节点了
	 */
	block = le32_to_cpu(gdp[desc].bg_inode_table) +
		(offset >> EXT2_BLOCK_SIZE_BITS(inode->i_sb));
	if (!(bh = sb_bread(inode->i_sb, block))) {
		ext2_error (inode->i_sb, "ext2_read_inode",
			    "unable to read inode block - "
			    "inode=%lu, block=%lu", inode->i_ino, block);
		goto bad_inode;
	}
	/*计算该索引节点在块中的偏移位置*/
	offset &= (EXT2_BLOCK_SIZE(inode->i_sb) - 1);
	/*得到索引节点*/
	raw_inode = (struct ext2_inode *) (bh->b_data + offset);

       /*从该节点raw_inode中读出信息填充inode*/
	inode->i_mode = le16_to_cpu(raw_inode->i_mode);
	inode->i_uid = (uid_t)le16_to_cpu(raw_inode->i_uid_low);
	inode->i_gid = (gid_t)le16_to_cpu(raw_inode->i_gid_low);
	if(!(test_opt (inode->i_sb, NO_UID32))) {
		inode->i_uid |= le16_to_cpu(raw_inode->i_uid_high) << 16;
		inode->i_gid |= le16_to_cpu(raw_inode->i_gid_high) << 16;
	}
	inode->i_nlink = le16_to_cpu(raw_inode->i_links_count);
	inode->i_size = le32_to_cpu(raw_inode->i_size);
	inode->i_atime = le32_to_cpu(raw_inode->i_atime);
	inode->i_ctime = le32_to_cpu(raw_inode->i_ctime);
	inode->i_mtime = le32_to_cpu(raw_inode->i_mtime);
	inode->u.ext2_i.i_dtime = le32_to_cpu(raw_inode->i_dtime);
	/* We now have enough fields to check if the inode was active or not.
	 * This is needed because nfsd might try to access dead inodes
	 * the test is that same one that e2fsck uses
	 * NeilBrown 1999oct15
	 */
	if (inode->i_nlink == 0 && (inode->i_mode == 0 || inode->u.ext2_i.i_dtime)) {
		/* this inode is deleted */
		brelse (bh);/*释放块在高速缓存中的缓冲区首部*/
		goto bad_inode;
	}
	inode->i_blksize = PAGE_SIZE;	/* This is the optimal IO size (for stat), not the fs block size */
	inode->i_blocks = le32_to_cpu(raw_inode->i_blocks);
	inode->i_version = ++event;
	inode->u.ext2_i.i_flags = le32_to_cpu(raw_inode->i_flags);
	inode->u.ext2_i.i_faddr = le32_to_cpu(raw_inode->i_faddr);
	inode->u.ext2_i.i_frag_no = raw_inode->i_frag;
	inode->u.ext2_i.i_frag_size = raw_inode->i_fsize;
	inode->u.ext2_i.i_file_acl = le32_to_cpu(raw_inode->i_file_acl);
	if (S_ISREG(inode->i_mode))
		inode->i_size |= ((__u64)le32_to_cpu(raw_inode->i_size_high)) << 32;
	else
		inode->u.ext2_i.i_dir_acl = le32_to_cpu(raw_inode->i_dir_acl);
	inode->i_generation = le32_to_cpu(raw_inode->i_generation);
	inode->u.ext2_i.i_prealloc_count = 0;
	inode->u.ext2_i.i_block_group = block_group;

	/*
	 * NOTE! The in-memory inode i_data array is in little-endian order
	 * even on big-endian machines: we do NOT byteswap the block numbers!
	 */
	for (block = 0; block < EXT2_N_BLOCKS; block++)
		inode->u.ext2_i.i_data[block] = raw_inode->i_block[block];

      /*赋上操作函数集实例*/
	if (inode->i_ino == EXT2_ACL_IDX_INO ||
	    inode->i_ino == EXT2_ACL_DATA_INO)
		/* Nothing to do */ ;
	else if (S_ISREG(inode->i_mode)) {
		inode->i_op = &ext2_file_inode_operations;
		inode->i_fop = &ext2_file_operations;
		inode->i_mapping->a_ops = &ext2_aops;
	} else if (S_ISDIR(inode->i_mode)) {
		inode->i_op = &ext2_dir_inode_operations;
		inode->i_fop = &ext2_dir_operations;
		inode->i_mapping->a_ops = &ext2_aops;
	} else if (S_ISLNK(inode->i_mode)) {
		if (!inode->i_blocks)
			inode->i_op = &ext2_fast_symlink_inode_operations;
		else {
			inode->i_op = &page_symlink_inode_operations;
			inode->i_mapping->a_ops = &ext2_aops;
		}
	} else 
		init_special_inode(inode, inode->i_mode,
				   le32_to_cpu(raw_inode->i_block[0]));
	brelse (bh);/*释放块在高速缓存中的缓冲区首部*/
	
	/*节点属性设置*/
	inode->i_attr_flags = 0;
	if (inode->u.ext2_i.i_flags & EXT2_SYNC_FL) {
		inode->i_attr_flags |= ATTR_FLAG_SYNCRONOUS;
		inode->i_flags |= S_SYNC;
	}
	if (inode->u.ext2_i.i_flags & EXT2_APPEND_FL) {
		inode->i_attr_flags |= ATTR_FLAG_APPEND;
		inode->i_flags |= S_APPEND;
	}
	if (inode->u.ext2_i.i_flags & EXT2_IMMUTABLE_FL) {
		inode->i_attr_flags |= ATTR_FLAG_IMMUTABLE;
		inode->i_flags |= S_IMMUTABLE;
	}
	if (inode->u.ext2_i.i_flags & EXT2_NOATIME_FL) {
		inode->i_attr_flags |= ATTR_FLAG_NOATIME;
		inode->i_flags |= S_NOATIME;
	}
	return;
	
bad_inode:
	make_bad_inode(inode);/*由于I/O错误，标记inode已损坏*/
	/*make_bad_inode - mark an inode bad due to an I/O error*/
	return;
}

/*更新索引节点*/
static int ext2_update_inode(struct inode * inode, int do_sync)
{
	struct buffer_head * bh;
	struct ext2_inode * raw_inode;
	unsigned long block_group;
	unsigned long group_desc;
	unsigned long desc;
	unsigned long block;
	unsigned long offset;
	int err = 0;
	struct ext2_group_desc * gdp;

       /*inode合法性检查*/
	if ((inode->i_ino != EXT2_ROOT_INO &&
	     inode->i_ino < EXT2_FIRST_INO(inode->i_sb)) ||
	    inode->i_ino > le32_to_cpu(inode->i_sb->u.ext2_sb.s_es->s_inodes_count)) {
		ext2_error (inode->i_sb, "ext2_write_inode",
			    "bad inode number: %lu", inode->i_ino);
		return -EIO;
	}
	
	/*块组号=索引节点号/每块组节点数*/
	block_group = (inode->i_ino - 1) / EXT2_INODES_PER_GROUP(inode->i_sb);
	/*如果索引节点所在的块组号>=文件系统中总块号*/
	if (block_group >= inode->i_sb->u.ext2_sb.s_groups_count) {
		ext2_error (inode->i_sb, "ext2_write_inode",
			    "group >= groups count");
		return -EIO;
	}
	/*块组描述符对应的块号=块组号*每块的块组描述符数*/
	group_desc = block_group >> EXT2_DESC_PER_BLOCK_BITS(inode->i_sb);
	/*计算描述符在块内的偏移*/
	desc = block_group & (EXT2_DESC_PER_BLOCK(inode->i_sb) - 1);
	/*通过s_group_desc[]数组找到这个组描述符所在块在高速缓存中的缓冲区首部*/
	bh = inode->i_sb->u.ext2_sb.s_group_desc[group_desc];
	if (!bh) {
		ext2_error (inode->i_sb, "ext2_write_inode",
			    "Descriptor not loaded");
		return -EIO;
	}
	/*得到描述符所在的buffer*/
	gdp = (struct ext2_group_desc *) bh->b_data;
	/*
	 * Figure out the offset within the block group inode table
	 */
	 /*节点在每块组内的偏移地址=索引节点号%每块节点数*节点大小*/
	offset = ((inode->i_ino - 1) % EXT2_INODES_PER_GROUP(inode->i_sb)) *
		EXT2_INODE_SIZE(inode->i_sb);
	/*计算块号*/
	block = le32_to_cpu(gdp[desc].bg_inode_table) +
		(offset >> EXT2_BLOCK_SIZE_BITS(inode->i_sb));
	/*读出节点表块*/
	if (!(bh = sb_bread(inode->i_sb, block))) {
		ext2_error (inode->i_sb, "ext2_write_inode",
			    "unable to read inode block - "
			    "inode=%lu, block=%lu", inode->i_ino, block);
		return -EIO;
	}
	/*块内偏移*/
	offset &= EXT2_BLOCK_SIZE(inode->i_sb) - 1;
	/*得到索引节点*/
	raw_inode = (struct ext2_inode *) (bh->b_data + offset);

       /*用inode填写row_inode*/
	raw_inode->i_mode = cpu_to_le16(inode->i_mode);
	if(!(test_opt(inode->i_sb, NO_UID32))) {
		raw_inode->i_uid_low = cpu_to_le16(low_16_bits(inode->i_uid));
		raw_inode->i_gid_low = cpu_to_le16(low_16_bits(inode->i_gid));
/*
 * Fix up interoperability with old kernels. Otherwise, old inodes get
 * re-used with the upper 16 bits of the uid/gid intact
 */
		if(!inode->u.ext2_i.i_dtime) {
			raw_inode->i_uid_high = cpu_to_le16(high_16_bits(inode->i_uid));
			raw_inode->i_gid_high = cpu_to_le16(high_16_bits(inode->i_gid));
		} else {
			raw_inode->i_uid_high = 0;
			raw_inode->i_gid_high = 0;
		}
	} else {
		raw_inode->i_uid_low = cpu_to_le16(fs_high2lowuid(inode->i_uid));
		raw_inode->i_gid_low = cpu_to_le16(fs_high2lowgid(inode->i_gid));
		raw_inode->i_uid_high = 0;
		raw_inode->i_gid_high = 0;
	}
	raw_inode->i_links_count = cpu_to_le16(inode->i_nlink);
	raw_inode->i_size = cpu_to_le32(inode->i_size);
	raw_inode->i_atime = cpu_to_le32(inode->i_atime);
	raw_inode->i_ctime = cpu_to_le32(inode->i_ctime);
	raw_inode->i_mtime = cpu_to_le32(inode->i_mtime);
	raw_inode->i_blocks = cpu_to_le32(inode->i_blocks);
	raw_inode->i_dtime = cpu_to_le32(inode->u.ext2_i.i_dtime);
	raw_inode->i_flags = cpu_to_le32(inode->u.ext2_i.i_flags);
	raw_inode->i_faddr = cpu_to_le32(inode->u.ext2_i.i_faddr);
	raw_inode->i_frag = inode->u.ext2_i.i_frag_no;
	raw_inode->i_fsize = inode->u.ext2_i.i_frag_size;
	raw_inode->i_file_acl = cpu_to_le32(inode->u.ext2_i.i_file_acl);
	if (S_ISDIR(inode->i_mode))
		raw_inode->i_dir_acl = cpu_to_le32(inode->u.ext2_i.i_dir_acl);
	else {
		raw_inode->i_size_high = cpu_to_le32(inode->i_size >> 32);
		if (inode->i_size > 0x7fffffffULL) {
			struct super_block *sb = inode->i_sb;
			if (!EXT2_HAS_RO_COMPAT_FEATURE(sb,
					EXT2_FEATURE_RO_COMPAT_LARGE_FILE) ||
			    EXT2_SB(sb)->s_es->s_rev_level ==
					cpu_to_le32(EXT2_GOOD_OLD_REV)) {
			       /* If this is the first large file
				* created, add a flag to the superblock.
				*/
				lock_kernel();
				ext2_update_dynamic_rev(sb);
				EXT2_SET_RO_COMPAT_FEATURE(sb,
					EXT2_FEATURE_RO_COMPAT_LARGE_FILE);
				unlock_kernel();
				ext2_write_super(sb);
			}
		}
	}
	
	raw_inode->i_generation = cpu_to_le32(inode->i_generation);
	if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode))
		raw_inode->i_block[0] = cpu_to_le32(kdev_t_to_nr(inode->i_rdev));
	else for (block = 0; block < EXT2_N_BLOCKS; block++)
		raw_inode->i_block[block] = inode->u.ext2_i.i_data[block];
	mark_buffer_dirty(bh);
	if (do_sync) {
		/*发出设备写请求*/
		ll_rw_block (WRITE, 1, &bh);
		/*在等待队列上等待buffer写入设备*/
		wait_on_buffer (bh);
		/*将buffer设置成req和uptodate状态*/
		if (buffer_req(bh) && !buffer_uptodate(bh)) {
			printk ("IO error syncing ext2 inode ["
				"%s:%08lx]\n",
				bdevname(inode->i_dev), inode->i_ino);
			err = -EIO;
		}
	}
	brelse (bh);/*释放块在高速缓存中的缓冲区首部*/
	return err;
}

/*将inode结构中数据写入到硬盘*/
void ext2_write_inode (struct inode * inode, int wait)
{
	lock_kernel();/*给内核上锁*/
	ext2_update_inode (inode, wait);/*调用更新inode的函数*/
	unlock_kernel();/*给内核解锁*/
}

/*把节点缓存中数据写入设备*/
int ext2_sync_inode (struct inode *inode)
{
	return ext2_update_inode (inode, 1);/*调用更新inode的函数*/
}