[Qemu-devel] Re: [PATCH v2 2/2] rbd: allow configuration of rados from the rbd filename

[Yoshiaki Tamura <tamura.yoshiaki@gmail.com>]

2011/4/8 Yehuda Sadeh Weinraub <yehudasa@gmail.com>:
> On Thu, Apr 7, 2011 at 2:54 AM, Yoshiaki Tamura
> <tamura.yoshiaki@gmail.com> wrote:
>> 2011/4/7 Stefan Hajnoczi <stefanha@gmail.com>:
>>> On Thu, Apr 07, 2011 at 10:14:03AM +0900, Yoshiaki Tamura wrote:
>>>> 2011/3/29 Josh Durgin <josh.durgin@dreamhost.com>:
>>>> > The new format is rbd:pool/image[@snapshot][:option1=value1[:option2=value2...]]
>>>> > Each option is used to configure rados, and may be any Ceph option, or "conf".
>>>> > The "conf" option specifies a Ceph configuration file to read.
>>>> >
>>>> > This allows rbd volumes from more than one Ceph cluster to be used by
>>>> > specifying different monitor addresses, as well as having different
>>>> > logging levels or locations for different volumes.
>>>> >
>>>> > Signed-off-by: Josh Durgin <josh.durgin@dreamhost.com>
>>>> > ---
>>>> >  block/rbd.c |  119 ++++++++++++++++++++++++++++++++++++++++++++++++++--------
>>>> >  1 files changed, 102 insertions(+), 17 deletions(-)
>>>> >
>>>> > diff --git a/block/rbd.c b/block/rbd.c
>>>> > index cb76dd3..bc3323d 100644
>>>> > --- a/block/rbd.c
>>>> > +++ b/block/rbd.c
>>>> > @@ -22,13 +22,17 @@
>>>> >  /*
>>>> >  * When specifying the image filename use:
>>>> >  *
>>>> > - * rbd:poolname/devicename
>>>> > + * rbd:poolname/devicename[@snapshotname][:option1=value1[:option2=value2...]]
>>>>
>>>> I'm not sure IIUC, but currently this @snapshotname seems to be
>>>> meaningless; it doesn't allow you to boot from a snapshot because it's
>>>> read only.  Am I misunderstanding or tested incorrectly?
>>>
>>> Read-only block devices are supported by QEMU and can be useful.
>>
>> I agree.  My expectation was that @snapshotname is introduced to have
>> writable snapshot.
>>
> The RADOS backend doesn't support writable snapshots. However, down
> the rbd roadmap we plan to have layering which in a sense is writable
> snapshots. The whole shift to librbd was done so that introducing such
> new functionality will be transparent and will not require much or any
> changes in the qemu code.

Thanks.  It made things clear :)  I think it's a good move.

Yoshi

>
> Yehuda
>