Thanks. I will give a new version in v3 of qcow2 shrink.
Jun Li
2014-9-3 上午1:12于 "Greg Kurz" <gk...@linux.vnet.ibm.com>写道：
> On Mon, 1 Sep 2014 18:52:48 +0800
> Jun Li <junm...@gmail.com> wrote:
>
> > When every item of refcount block is NULL, free refcount block and reset
> the
> > corresponding item of refcount table with NULL.
> >
> > Signed-off-by: Jun Li <address@hidden>
> > ---
> >
> > The v2 do following change to modify some potential issue.
> >
> > +------- Here should start from "0".
> > |
> > for (k = 0; k < refcount_block_entries; k++) {
> > if (refcount_block[k] != cpu_to_be16(0)) {
> > ... | |
> > } | |
> > } | +---- Using "0" is more
> safe.
> > |
> > +-------- This should be "k" not "++k".
> > ---
> > block/qcow2-refcount.c | 31 +++++++++++++++++++++++++++++++
> > 1 file changed, 31 insertions(+)
> >
> > diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
> > index 43665b8..63f36e6 100644
> > --- a/block/qcow2-refcount.c
> > +++ b/block/qcow2-refcount.c
> > @@ -586,6 +586,37 @@ static int QEMU_WARN_UNUSED_RESULT
> update_refcount(BlockDriverState *bs,
> > if (refcount == 0 && s->discard_passthrough[type]) {
> > update_refcount_discard(bs, cluster_offset,
> s->cluster_size);
> > }
> > +
> > + /* When refcount block is NULL, update refcount table */
> > + if (block_index == 0) {
> > + int k = block_index;
>
> Hi,
>
> k = 0 is also done in the for block below...
>
> > + int refcount_block_entries = s->cluster_size /
> sizeof(uint16_t);
>
> It's better for maintainance to count elements in an array this way:
>
> int refcount_block_entries = s->cluster_size / sizeof(refcount_block[0]);
>
> > + for (k = 0; k < refcount_block_entries; k++) {
> > + if (refcount_block[k] != cpu_to_be16(0)) {
> > + break;
> > + }
> > + }
> > +
> > + if (k == refcount_block_entries) {
> > + qemu_vfree(refcount_block);
> > + /* update refcount table */
> > + unsigned int refcount_table_index;
> > + uint64_t data64 = cpu_to_be64(0);
> > + refcount_table_index = cluster_index >>
> (s->cluster_bits -
> > + REFCOUNT_SHIFT);
> > + ret = bdrv_pwrite_sync(bs->file,
> > + s->refcount_table_offset +
> > + refcount_table_index *
> > + sizeof(uint64_t),
> > + &data64, sizeof(data64));
> > + if (ret < 0) {
> > + goto fail;
> > + }
> > +
> > + s->refcount_table[refcount_table_index] = data64;
> > +
> > + }
> > + }
> > }
> >
> > ret = 0;
>
> Cheers.
>
> --
> Gregory Kurz kurzg...@fr.ibm.com
> gk...@linux.vnet.ibm.com
> Software Engineer @ IBM/Meiosys http://www.ibm.com
> Tel +33 (0)562 165 496
>
> "Anarchy is about taking complete responsibility for yourself."
> Alan Moore.
>
>
