Re: [Qemu-devel] [PATCH 21/22] specs/qcow2: fix bitmap granularity qemu-specific note

[Vladimir Sementsov-Ogievskiy]

07.10.2016 23:18, Eric Blake wrote:
> On 09/30/2016 05:53 AM, Vladimir Sementsov-Ogievskiy wrote:
> > Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> > ---
> >   docs/specs/qcow2.txt | 3 +--
> >   1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/docs/specs/qcow2.txt b/docs/specs/qcow2.txt
> > index 80cdfd0..d3e292f 100644
> > --- a/docs/specs/qcow2.txt
> > +++ b/docs/specs/qcow2.txt
> > @@ -472,8 +472,7 @@ Structure of a bitmap directory entry:
> >                17:    granularity_bits
> >                       Granularity bits. Valid values: 0 - 63.
> Can we really theoretically go as low as 0, or are we constrained by the
> fact that cluster_bits must be at least 9?

Bitmaps in qcow2 are abstract, they are not necessary related to 
BdrvDirtyBitmaps.. We do not know how the will be used in future, so 
there no reasons for hard restriction. However values near zero seems 
not very useful. I do not think we should change this. Note about Qemu 
is enough.


> >   
> > -                    Note: Qemu currently doesn't support granularity_bits
> > -                    greater than 31.
> > +                    Note: Qemu currently support only values 9 - 31.
> s/support/supports/
>
> >   
> >                       Granularity is calculated as
> >                           granularity = 1 << granularity_bits


--
Best regards,
Vladimir