Re: [Qemu-block] [PATCH v5 11/11] nbd-server: Allow node name for nbd-server-add

[Max Reitz]

On 03.08.2016 13:21, Kevin Wolf wrote:
> There is no reason why an NBD server couldn't be started for any node,
> even if it's not on the top level. This converts nbd-server-add to
> accept a node-name.
> 
> Note that there is a semantic difference between using a BlockBackend
> name and the node name of its root: In the former case, the NBD server
> is closed on eject; in the latter case, the NBD server doesn't drop its
> reference and keeps the image file open this way.
> 
> Signed-off-by: Kevin Wolf <address@hidden>
> ---
>  blockdev-nbd.c  | 21 +++++++++------------
>  qapi/block.json |  4 ++--
>  2 files changed, 11 insertions(+), 14 deletions(-)

Well, while I concede that it's possible to create R/W NBD servers on
basically any node even today, I share Eric's concern that we shouldn't
make it so simple.

On the other hand, given COLO, I can't think of any simple solution to
this. As far as I'm aware, COLO will make use of R/W NBD servers on
backing nodes, so we can't just disallow creation of R/W servers on
non-root nodes.

So I guess your take on this is that it was already possible to create
NBD servers wherever you so pleased and that we should just put this off
until we have better op blockers?

Max

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