Re: [Qemu-devel] [PATCH 25/25] hmp: add NBD server commands

[Paolo Bonzini]

Il 19/10/2012 14:44, Markus Armbruster ha scritto:
> Apropos hotplug.  The only way to unexport a block device is to stop the
> NBD server outright.  Once the device backend has been exported,
> unplugging the device gets rid of the frontend, but the backend stays
> until you stop the NBD server, or you kill the backend with the big
> drive_del hammer.

Right.  (Though for removable devices you can just eject it, which calls
the close notifier).

> Makes me wonder whether we need QMP command nbd-server-del.

Perhaps yes, but it can be added later.

> I agree that we can the human monitor is again for human users only,
> thus we don't have to encumber it with the need of tools.  I might also
> buy your argument that extra exports don't really hurt.  But device plug
> / -unplug is just as relevant there as in QMP.  If it's a show-stopper
> for QMP, then I don't think it can be a "minor loss" for HMP.

The question is, who do we expect to use HMP at this time?

> 2. What if we ever change our minds regarding fine-grained NBD export
> control in the human monitor?  Add a second command to start the server
> without exporting everything?  Add a "don't auto-export" argument to the
> existing command?

The latter.

But indeed one alternative, possibly better, is to remove the auto-add
and add a "nbd_server_add -a" (for "all") flag to HMP.  I think I'll
drop the last patch and send a pull request for the others (with your
suggested changes), while we discuss this.

Paolo