open image file

[horseriver]

hi:)

  I have a image file ,after I input this command:
  
  ******
  sh> losetup /dev/loop0 xx.img 
  sh>  mount -t tmpfs /dev/loop0 /mnt 

  ******


 I find no content under /mnt ,But this image file contains a bootloader.
 What is the reason ? How can I check out the file tree structure  of this image ?

thanks!