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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Thu, 24 Mar 2016 12:58:28 +0100
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Subject: Re: [Qemu-devel] [Nbd] [PATCH 2/2] NBD proto: add GET_LBA_STATUS
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To: Alex Bligh <alex@alex.org.uk>, Wouter Verhelst <w@uter.be>
Cc: "nbd-general@lists.sourceforge.net" <nbd-general@lists.sourceforge.net>, Kevin Wolf <kwolf@redhat.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, Pavel Borzenkov <pborzenkov@virtuozzo.com>, "Stefan stefanha@redhat. com" <stefanha@redhat.com>, "Denis V. Lunev" <den@openvz.org>



On 24/03/2016 11:32, Alex Bligh wrote:
>> > Now I'm not saying we
>> > need to fully define what it means for a part of the backend to be
>> > "dirty" or not.  It's okay to leave part of the meaning in the dark,
>> > leaving that implementation-defined.
> Well, the 3 possible states are:
>=20
> * unallocated
> * zero
> * non-zero
>=20
> So the possible replies are a bitfield of those, with a '1' if it 'migh=
t'
> be in that state, i.e.
>=20
> 111 =3D no idea
> 110 =3D might be zero or unallocated, but isn't zero
> 011 =3D I know it's allocated, but I don't know whether it is zero or n=
ot

How do you represent "definitely unallocated?"

Paolo

> And '000' is not permitted!