Hi, I'm learning the kernel of 0.12, and the function in inode.c: #################################################################### static int _bmap(struct m_inode * inode,int block,int create) { struct buffer_head * bh; int i; if (block<0) panic("_bmap: block<0"); if (block >= 7+512+512*512) panic("_bmap: block>big"); if (block<7) { if (create && !inode->i_zone[block]) if (inode->i_zone[block]=new_block(inode->i_dev)) { inode->i_ctime=CURRENT_TIME; inode->i_dirt=1; } return inode->i_zone[block]; } block -= 7; if (block<512) { if (create && !inode->i_zone[7]) if (inode->i_zone[7]=new_block(inode->i_dev)) { inode->i_dirt=1; inode->i_ctime=CURRENT_TIME; } if (!inode->i_zone[7]) return 0; if (!(bh = bread(inode->i_dev,inode->i_zone[7]))) return 0; i = ((unsigned short *) (bh->b_data))[block]; if (create && !i) if (i=new_block(inode->i_dev)) { ((unsigned short *) (bh->b_data))[block]=i; bh->b_dirt=1; } brelse(bh); return i; } block -= 512; if (create && !inode->i_zone[8]) if (inode->i_zone[8]=new_block(inode->i_dev)) { inode->i_dirt=1; inode->i_ctime=CURRENT_TIME; } if (!inode->i_zone[8]) return 0; if (!(bh=bread(inode->i_dev,inode->i_zone[8]))) return 0; i = ((unsigned short *)bh->b_data)[block>>9]; if (create && !i) if (i=new_block(inode->i_dev)) { ((unsigned short *) (bh->b_data))[block>>9]=i; bh->b_dirt=1; } brelse(bh); if (!i) return 0; if (!(bh=bread(inode->i_dev,i))) return 0; i = ((unsigned short *)bh->b_data)[block&511]; if (create && !i) if (i=new_block(inode->i_dev)) { ((unsigned short *) (bh->b_data))[block&511]=i; bh->b_dirt=1; } brelse(bh); return i; } ######################################################################## "if (block >= 7+512+512*512)" because the i_zone[9]. But the question is why the i_zone[7] can repesent 512 , and i_zone[8] can repesent 512*512 ? Thank you.