Re: [PATCH v2 3/5] a standone-alone tool to directly share disk image file via vhost-user protocol

[Coiby Xu <coiby.xu@gmail.com>]

> > > Yes, I think at least for the moment it should work fine this way.
> > > Eventually, I'd like to integrate it with --export (and associated QMP
> > > commands, which are still to be created), too. Maybe at that point we
> > > want to make the QOM object not user creatable any more.
> >
> > Does it mean TYPE_USER_CREATABLE interface in QOM will become
> > deprecated in the future? I'm curious what are the reasons for making
> > QOM object no user creatable? Because we may still need to start
> > vhost-user block device backend through HMP or QMP instead of stating
> > it as a standalone-alone daemon.

> Not in general, but if we have something like a block-export-add QMP
> command, the QOM interface would be redundant. We could still leave it
> there and have both a low-level and a high-level interface, but whether
> we would want to is something we still have to decide.

I see. So QOM interface will still be used as a low-level interface.
In the draft version, vhost-user-blk-server is started using specific
command vhost_user_server_start/vhost_user_server_stop which proivide
interfaces easier for implementing block-export-add QMP command. But
in later versions, only object_add/object_del syntax is supported to
start/stop vhost-user-blk-server. I'll keep an eye on how the storage
daemon develops and adapt my code accordingly.


On Sun, Feb 2, 2020 at 5:33 PM Kevin Wolf <kwolf@redhat.com> wrote:
>
> Am 31.01.2020 um 17:42 hat Coiby Xu geschrieben:
> > > Yes, I think at least for the moment it should work fine this way.
> > > Eventually, I'd like to integrate it with --export (and associated QMP
> > > commands, which are still to be created), too. Maybe at that point we
> > > want to make the QOM object not user creatable any more.
> >
> > Does it mean TYPE_USER_CREATABLE interface in QOM will become
> > deprecated in the future? I'm curious what are the reasons for making
> > QOM object no user creatable? Because we may still need to start
> > vhost-user block device backend through HMP or QMP instead of stating
> > it as a standalone-alone daemon.
>
> Not in general, but if we have something like a block-export-add QMP
> command, the QOM interface would be redundant. We could still leave it
> there and have both a low-level and a high-level interface, but whether
> we would want to is something we still have to decide.
>
> > > As for test cases, do you think it would be hard to just modify the
> > > tests to send an explicit 'quit' command to the daemon?
> >
> > Accroding to https://patchew.org/QEMU/20191017130204.16131-1-kwolf@redhat.com/20191017130204.16131-10-kwolf@redhat.com/,
> >
> > > +static bool exit_requested = false;
> > > +
> > > +void qemu_system_killed(int signal, pid_t pid)
> > > +{
> > > +    exit_requested = true;
> > > +}
> >
> > if exit_requested = true, qemu-storage-daemon will exit the main loop
> > and then quit. So is calling qemu_system_killed by what you means "to
> > send an explicit 'quit' command to the daemon"?
>
> qemu_system_killed() is call in the signal handlers for, amongst others,
> SIGTERM and SIGINT. This is one way to stop the storage daemon (for
> manual use, sending SIGINT with Ctrl-C is probably the easiest way).
>
> What I actually meant is the 'quit' QMP command which will cause
> qmp_quit() to be run, which contains the same code. But if sending a
> signal is more convenient, that's just as good.
>
> Kevin
>
> > On Fri, Jan 17, 2020 at 6:12 PM Kevin Wolf <kwolf@redhat.com> wrote:
> > >
> > > Am 17.01.2020 um 09:12 hat Coiby Xu geschrieben:
> > > > Excellent! I will add an option (or object property) for
> > > > vhost-user-blk server oject which will tell the daemon process to exit
> > > > when the client disconnects, thus "make check-qtest" will not get held
> > > > by this daemon process. After that since Kevin's qemu-storage-daemon
> > > > support "-object" option
> > > > (https://patchew.org/QEMU/20191017130204.16131-1-kwolf@redhat.com/20191017130204.16131-3-kwolf@redhat.com/)
> > > > and vhost-user-server is a user-creatable QOM object, it will work out
> > > > of the box.
> > >
> > > Yes, I think at least for the moment it should work fine this way.
> > > Eventually, I'd like to integrate it with --export (and associated QMP
> > > commands, which are still to be created), too. Maybe at that point we
> > > want to make the QOM object not user creatable any more.
> > >
> > > Would it make sense to prefix the object type name with "x-" so we can
> > > later retire it from the external user interface without a deprecation
> > > period?
> > >
> > > As for test cases, do you think it would be hard to just modify the
> > > tests to send an explicit 'quit' command to the daemon?
> > >
> > > > I'm curious when will be formal version of qemu-storage-daemon
> > > > finished so I can take advantage of it? Or should I apply the RFC
> > > > PATCHes to my working branch directly and submit them together with
> > > > the patches on vhost-user-blk server feature when posting v3?
> > >
> > > It's the next thing I'm planning to work on after completing the
> > > coroutine-base QMP handlers (which I hope to get finished very soon).
> > >
> > > For the time being I would suggest that you put any patches that depend
> > > on qemu-storage-daemon (if you do need it) at the end of your series so
> > > that we could apply the first part even if the storage daemon isn't in
> > > yet.
> > >
> > > The latest version of my patches is at:
> > >
> > >     git://repo.or.cz/qemu/kevin.git storage-daemon
> > >
> > > But if you just need something for testing your code, I think it would
> > > even make sense if you kept your standalone tool around (even though
> > > we'll never merge it) and we'll deal with integration in the storage
> > > daemon once both parts are ready.
> > >
> > > Kevin
> > >
> >
> >
> > --
> > Best regards,
> > Coiby
> >
>


--
Best regards,
Coiby