Re: [Qemu-devel] [PATCH 2/2] qapi: Allow blockdev-add for NBD

[Kevin Wolf]

Am 03.02.2016 um 18:06 hat Daniel P. Berrange geschrieben:
> 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

That's patch 1 of a series that has a few more dependencies. Can the
patch be applied without the rest of the series (and without the
dependencies) so that we don't have to wait for a very long time with
Max's patches?

> > - 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.

Agreed. Anything in SocketAddress that isn't supported is either a bug
or a missing feature.

Kevin