/*
 * Ok, we do readpage, to be able to execute programs.  Unfortunately,
 * we can't use bmap, since we may have looser alignments.
 */

static int
romfs_readpage(struct file *file, struct page * page)
{
 struct inode *inode = page->mapping->host;
 unsigned long offset, avail, readlen;
 void *buf;
 int result = -EIO;

 page_cache_get(page);
 lock_kernel();
 buf = kmap(page);
 if (!buf)
  goto err_out;

 /* 32 bit warning -- but not for us :) */
 offset = page->index << PAGE_CACHE_SHIFT;

 //inode->i_size只有普通文件＆符号链接文件
 if (offset < inode->i_size) {
  //avail表明剩余的字节数
  avail = inode->i_size-offset;
  //读取一页还是avail
  readlen = min_t(unsigned long, avail, PAGE_SIZE);
 
  if (romfs_copyfrom(inode, buf, inode->u.romfs_i.i_dataoffset+offset, readlen) == readlen) {
   //页面尾部填充零
   if (readlen < PAGE_SIZE) {
    memset(buf + readlen,0,PAGE_SIZE-readlen);
   }
   SetPageUptodate(page);
   result = 0;
  }
 }
 //错误处理
 if (result) {
  memset(buf, 0, PAGE_SIZE);
  SetPageError(page);
 }
 flush_dcache_page(page);

 UnlockPage(page);

 kunmap(page);
err_out:
 page_cache_release(page);
 unlock_kernel();

 return result;
}

/* Mapping from our types to the kernel */

static struct address_space_operations romfs_aops = {
 readpage: romfs_readpage
};

static struct file_operations romfs_dir_operations = {
 read:  generic_read_dir,
 readdir: romfs_readdir,
};

static struct inode_operations romfs_dir_inode_operations = {
 lookup:  romfs_lookup,
};

//权限映射表
static mode_t romfs_modemap[] =
{
 0, S_IFDIR+0644, S_IFREG+0644, S_IFLNK+0777,
 S_IFBLK+0600, S_IFCHR+0600, S_IFSOCK+0644, S_IFIFO+0644
};

static void
romfs_read_inode(struct inode *i)
{
 int nextfh, ino;
 struct romfs_inode ri;

 ino = i->i_ino & ROMFH_MASK;
 i->i_mode = 0;

 /* Loop for finding the real hard link */
 for(;;) {
  //根据ino作为offset获取16字节的文件头
  if (romfs_copyfrom(i, &ri, ino, ROMFH_SIZE) <= 0) {
   printk("romfs: read error for inode 0x%x\n", ino);
   return;
  }
  /* XXX: do romfs_checksum here too (with name) */

  nextfh = ntohl(ri.next);
  //当前文件节点是否是硬链接
  if ((nextfh & ROMFH_TYPE) != ROMFH_HRD)
   break;
  //如果是硬链接，spec.info保存对应的地址
  //由于ino和offset一致，所以重新读取节点
  ino = ntohl(ri.spec) & ROMFH_MASK;
 }

 //到此只是得到了文件头信息
 i->i_nlink = 1;  /* Hard to decide.. */
 i->i_size = ntohl(ri.size);
 i->i_mtime = i->i_atime = i->i_ctime = 0;
 i->i_uid = i->i_gid = 0;