On Mon, Aug 25, 2014 at 12:38:06AM +0800, Jun Li wrote: > Why bdrv_discard does not yet pass the discard on to the underlying file > system driver? And this exist a potential issue: host cluster leak for > qcow2. As qcow2 image can be created on RAW disk, > so this is not just "does not yet pass the discard on to the underlying file > system driver". Could you give some explanation why do not realize this > function? Thx. > > As I am trying to realize qcow2 shrinking, but hit bdrv_discard can not > release the free cluster on host.
qcow2 is capable of passing discards down to the image file. See qcow2_process_discards(). It is important that s->discard_passthrough[QCOW2_DISCARD_REQUEST] is true! Make sure to use the pass-discard-request=on or discard=unmap options. Stefan
pgpTFEuH0KVho.pgp
Description: PGP signature
