title: Reading contents of a qcow2 image using `bdrv_pread(..)` or alternatives
body: <p>I wanted to read contents off a <code>.qcow2</code> image using <code>bdrv_pread(...)</code> functions in QEMU.
  Say, the full path of my image is <code>/path/to/myimage.qcow2</code>, I want to be able to read 'n' bytes of data off of this image at a particular offset. Now the <code>bdrv_pread</code> functions takes these arguments '<code>BlockDriverState *bs, int64_t offset, void *buf, int count1</code>', how exactly do I initialize the <code>BlockDriverState</code> (device?) from the path of the image. All other parameters other than <code>BlockDriverState</code> are clear to me.</p>
  
  <p>Thanks.</p>