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Re: [Qemu-devel] [PATCH 2/2] qapi: Allow blockdev-add for NBD
From: |
Daniel P. Berrange |
Subject: |
Re: [Qemu-devel] [PATCH 2/2] qapi: Allow blockdev-add for NBD |
Date: |
Wed, 3 Feb 2016 17:06:09 +0000 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
On Wed, Feb 03, 2016 at 05:33:16PM +0100, Max Reitz wrote:
> We have to introduce a new object (BlockdevOptionsNbd) for several
> reasons:
> - Neither of InetSocketAddress nor UnixSocketAddress alone is
> sufficient, because both are supported
> - We cannot use SocketAddress because NBD does not support an fd,
> and because it is not a flat union which BlockdevOptionsNbd is
With my patch series that converts NBD to use QIOChannel, all the
entry points for client & server *do* take a SocketAddress struct
to provide address info. So internally the code does in fact allow
use of an FD, if there were a way to specify it a the QAPI level...
eg see
https://lists.gnu.org/archive/html/qemu-devel/2016-01/msg04159.html
> - We cannot use a flat union of InetSocketAddress and
> UnixSocketAddress because we would need some kind of discriminator
> which we do not have; we could inline the UnixSocketAddress as a
> string and then make it an 'alternate' type instead of a union, but
> this will not work either, because:
> - InetSocketAddress itself is not suitable for NBD because the port is
> not optional (which it is for NBD) and because it offers more options
> (like choosing between ipv4 and ipv6) which NBD does not support.
The *should* support ipv4 and ipv6 options for NBD. We should also make
the port optional in the SocketAddress struct - I tried to do that previously
but my patch was flawed, but we should revisit this.
So IMHO all the things you list above are reasons *for* using SocketAddress
and not re-inventing it poorly with explicit host + port fields.
Regards,
Daniel
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