Re: [Qemu-devel] [PATCH v2 1/1] parallels: add format spec

[Vladimir Sementsov-Ogievskiy]

On 26.11.2015 11:17, Stefan Hajnoczi wrote:
> On Mon, Nov 23, 2015 at 04:32:37PM +0300, Denis V. Lunev wrote:
> > From: Vladimir Sementsov-Ogievskiy <address@hidden>
> >
> > This specifies Parallels image format as implemented in Parallels Cloud
> > Server 6.10
> >
> > Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> > Signed-off-by: Denis V. Lunev <address@hidden>
> > CC: Eric Blake <address@hidden>
> > CC: John Snow <address@hidden>
> > CC: Stefan Hajnoczi <address@hidden>
> > ---
> > v2: add license info
> >      switch to offsets from types in field descriptions
> Cool!  Thanks for publishing a specification.  This will help everyone
> understand the code.
>
> > +=== Dirty bitmaps feature ===
> > +
> > +This feature provides a way of storing dirty bitmaps in the image. The fields
> > +of its data area are:
> > +
> > +   0 -  7:    size
> > +              The bitmap size, should be equal to disk size in sectors.
> > +
> > +   8 - 23:    id
> > +              An identifier for backup consistency checking.
> > +
> > +  24 - 27:    granularity
> > +              Bitmap granularity, in sectors. I.e., the number of sectors
> > +              corresponding to one bit of the bitmap.
> Does this need to be a power of 2?

Good point

> > +  28 - 31:    l1_size
> > +              The number of entries in the L1 table of the bitmap.
> > +
> > +  variable:   l1 (64 * l1_size bytes)
> > +              L1 offset table (in bytes)
> > +
> > +A dirty bitmap is stored using a one-level structure for the mapping to host
> > +clusters - an L1 table.
> > +
> > +Given an offset into the bitmap, the offset in bytes into the image file can be
> What are the units of the offset into the bitmap?  Is it a bit number
> (i.e. sector number / granularity)?

No, here bitmap is considered as raw data, stored using L1, so offset is 
in bytes. Bytes of the bitmap itself, as raw binary data.

--
Best regards,
Vladimir
* now, @virtuozzo.com instead of @parallels.com. Sorry for this inconvenience.