Re: [Qemu-stable] [Qemu-devel] [PATCH 1/3] block/qcow2: refactoring of threaded encryption code

[Maxim Levitsky]

On Fri, 2019-09-06 at 14:00 -0500, Eric Blake wrote:
> On 9/6/19 1:55 PM, Maxim Levitsky wrote:
> 
> > > > +/*
> > > > + * qcow2_co_encrypt()
> > > > + *
> > > > + * Encrypts a sector size aligned contiguous area
> > > > + *
> > > > + * @host_cluster_offset - on disk offset of the cluster in which
> > > > + *                        the buffer resides
> > > > + *
> > > > + * @guest_offset - guest (virtual) offset of the buffer
> > > > + * @buf - buffer with the data to encrypt
> > > > + * @len - length of the buffer
> > > > + *
> > > > + * Note that the area is not cluster aligned and might cross a cluster
> > > > + * boundary
> > > 
> > > Umm, how is it possible for a sector to cross a cluster boundary?  All
> > > clusters are sector-aligned, and encryption only works on aligned
> > > sectors.  Oh, I see - if @len is a multiple larger than sector size,
> > > then we have multiple sectors, and then indeed we may cross clusters.
> > > But then the docs about being 'a sector size aligned contiguous area' is
> > > not quite right.
> > 
> > Why? the written area is always both aligned on _sector_ boundary
> > and multiple of the sector size. At least that what I see from
> > the existing asserts.
> 
> I'm thinking it should read something like:
> 
> Encrypts one or more contiguous aligned sectors
> 
> to make it obvious that because there can be multiple sectors, there may
> indeed be a cluster boundary mid-length.  My complaint was that the
> original text made it sound like there was exactly one sector (at which
> point @len is redundant, unless sectors are variably-sized)
> 
I agree with you completely, I will change that.

Best regards,
        Maxim Levitsky