e4a86f88cc
qemu-img convert can assume "that sectors which are unallocated in the input image are present in both the output's and input's base images". However it is only doing this if the output image returns true for bdrv_has_zero_init(). Testing bdrv_has_zero_init() does not make much sense if the output image is copy-on-write, because a copy-on-write image is never initialized to zero (it is initialized to the content of the backing file). There is nothing here that makes has_zero_init images special. The input and output must be equal for the operation to make sense, and that's it. Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Read the documentation in qemu-doc.html or on http://wiki.qemu.org - QEMU team