Re: [RFC PATCH 06/18] qemu-storage-daemon: Add --nbd-server option

[Kevin Wolf]

Am 06.11.2019 um 20:25 hat Eric Blake geschrieben:
> On 11/6/19 6:51 AM, Max Reitz wrote:
> > On 17.10.19 15:01, Kevin Wolf wrote:
> > > Add a --nbd-server option to qemu-storage-daemon to start the built-in
> > > NBD server right away. It maps the arguments for nbd-server-start to the
> > > command line.
> > 
> > Well, it doesn’t quite, because nbd-server-start takes a
> > SocketAddressLegacy, and this takes a SocketAddress.
> > 
> > On one hand I can understand why you would do it differently (especially
> > for command-line options), but on the other I find it a bit problematic
> > to have --nbd-server be slightly different from nbd-server-start when
> > both are intended to be the same.
> > 
> > My biggest problem though lies in the duplication in the QAPI schema.
> > If NbdServerOptions.addr were a SocketAddressLegacy, we could let
> > nbd-server-start’s options just be of type NbdServerOptions and thus get
> > rid of the duplication.
> 
> I would love to somehow deprecate the use of SocketAddressLegacy and get QMP
> nbd-server-start to accept SocketAddress instead.  Maybe it could be done by
> adding a new nbd-server-begin command in 5.0 with a saner wire layout, and
> deprecating nbd-server-start at that time; by the 5.2 release, we could then
> drop nbd-server-start.  But we're too late for 4.2.

As a replacement nbd-server-add, I envisioned adding something like a
block-export-add, which would work the way that --export already does.
It would also come with query-block-exports and block-export-del, and it
wouldn't contain only NBD devices, but also vhost-user, FUSE, etc.
exports.

Now I'm wondering if the same would make sense for nbd-server-start.
Maybe an API change would even allow us to start multiple NBD servers
(e.g. listening on different IP addresses or using different tls-creds).

Kevin