Re: [Qemu-devel] [PATCH v2 3/5] qcow2: Make copy_sectors() byte based

[Kevin Wolf <kwolf@redhat.com>]

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Am 07.06.2016 um 05:47 hat Eric Blake geschrieben:
> On 06/06/2016 08:59 AM, Kevin Wolf wrote:
> > This will allow copy on write operations where the overwritten part of
> > the cluster is not aligned to sector boundaries.
> > 
> > Also rename the function because it has nothing to do with sectors any
> > more.
> > 
> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> > ---
> >  block/qcow2-cluster.c | 54 +++++++++++++++++++++++++--------------------------
> >  1 file changed, 26 insertions(+), 28 deletions(-)
> > 
> 
> >  
> >      if (bs->encrypted) {
> >          Error *err = NULL;
> > +        int sector = (cluster_offset + offset_in_cluster) >> BDRV_SECTOR_BITS;
> 
> Potentially the wrong type...

Yes, thanks for catching that.

> >          assert(s->cipher);
> > -        if (qcow2_encrypt_sectors(s, start_sect + n_start,
> > -                                  iov.iov_base, iov.iov_base, n,
> > -                                  true, &err) < 0) {
> > +        assert((offset_in_cluster & BDRV_SECTOR_MASK) == 0);
> 
> Why is this one true? If I have a cluster of 4 sectors, why must
> offset_in_cluster fall within only the first of those sectors?  Are you
> missing a ~, to instead be asserting that offset_in_cluster is
> sector-aligned?

You mean I should actually test encrypted images? *cough* (I know I did
test something with encryption, but maybe that was only after converting
reads.)

Anyway, missing ~ indeed.

> > +        assert((bytes & ~BDRV_SECTOR_MASK) == 0);
> 
> This one looks correct, stating that the number of bytes to copy is a
> sector multiple.
> 
> > +        if (qcow2_encrypt_sectors(s, sector, iov.iov_base, iov.iov_base,
> > +                                  bytes >> BDRV_SECTOR_BITS, true, &err) < 0) {
> 
> ...since encryption allows a 64-bit sector number for the case where the
> image is larger than 2T.

Kevin

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