On 02/29/2016 07:59 AM, Eric Blake wrote: >> an L2 entry value of 4A C0 00 00 00 3D 97 50. > > So with default 64k clusters, x = 62 - (16 - 8) = 54. Bits 0-54 are the > host cluster offset, or 0x003d9750, but that is in terms of host > sectors. The comment in block/qcow2.c is telling, and perhaps we should > improve the qcow2 spec to make it obvious: > > - Size of compressed clusters is stored in sectors to reduce bit usage > in the cluster offsets. > > Thus, in your image, the guest compressed data starts at sector > 0x003d9750, or host file offset 0x7b2ea000. This value is NOT aligned > to a cluster, but IS aligned to a sector (since a sector is the smallest > unit we write to), and makes more sense than something ending in 0x50 > (which is not sector aligned).
Disclaimer - I did not test things, so I may be misreading the spec myself. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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