ext2文件系统读取 索引节点信息代码：
void ext2_read_inode (struct inode * inode){ 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; struct ext2_group_desc * gdp; 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; } //块组号 block_group = (inode->i_ino - 1) / EXT2_INODES_PER_GROUP(inode->i_sb); 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; } //对于该块组描述符所在的逻辑块号 group_desc = block_group >> EXT2_DESC_PER_BLOCK_BITS(inode->i_sb); //该inode对应的块组描述符在该逻辑块中的偏移 desc = block_group & (EXT2_DESC_PER_BLOCK(inode->i_sb) - 1); 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; } gdp = (struct ext2_group_desc *) bh->b_data; /* * Figure out the offset within the block group inode table */ //该inode在该块组中，相对于inode节点起始地址的偏移 offset = ((inode->i_ino - 1) % EXT2_INODES_PER_GROUP(inode->i_sb)) * EXT2_INODE_SIZE(inode->i_sb); /*块组描述符.bg_inode_table: Block number of first inode table block,即inode节点表的起始逻辑块号，所以off需要除以块大小，1K */ 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; } /*由于sb_bread已经把inode所在的逻辑块block读入到bh中，所以offset应是相对于该块起始地址的偏移，即offset如下 */ offset &= (EXT2_BLOCK_SIZE(inode->i_sb) - 1); raw_inode = (struct ext2_inode *) (bh->b_data + offset); 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); 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]; 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); 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); return;}
inode到硬盘的过程：
