On Thu, Oct 19, 2017 at 10:15:48PM -0200, Eduardo Habkost wrote:
> On Thu, Oct 19, 2017 at 09:42:18PM +1100, David Gibson wrote:
> > On Mon, Oct 16, 2017 at 02:59:16PM -0200, Eduardo Habkost wrote:
> > > On Mon, Oct 16, 2017 at 06:22:54PM +0200, Igor Mammedov wrote:
> > > > Signed-off-by: Igor Mammedov <imamm...@redhat.com>
> > > > ---
> > > > include/sysemu/sysemu.h | 1 +
> > > > qemu-options.hx | 15 ++++++++++++++
> > > > qmp.c | 5 +++++
> > > > vl.c | 54
> > > > ++++++++++++++++++++++++++++++++++++++++++++++++-
> > > > 4 files changed, 74 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
> > > > index b213696..3feb94f 100644
> > > > --- a/include/sysemu/sysemu.h
> > > > +++ b/include/sysemu/sysemu.h
> > > > @@ -66,6 +66,7 @@ typedef enum WakeupReason {
> > > > QEMU_WAKEUP_REASON_OTHER,
> > > > } WakeupReason;
> > > >
> > > > +void qemu_exit_preconfig_request(void);
> > > > void qemu_system_reset_request(ShutdownCause reason);
> > > > void qemu_system_suspend_request(void);
> > > > void qemu_register_suspend_notifier(Notifier *notifier);
> > > > diff --git a/qemu-options.hx b/qemu-options.hx
> > > > index 39225ae..bd44db8 100644
> > > > --- a/qemu-options.hx
> > > > +++ b/qemu-options.hx
> > > > @@ -3498,6 +3498,21 @@ STEXI
> > > > Run the emulation in single step mode.
> > > > ETEXI
> > > >
> > > > +DEF("paused", HAS_ARG, QEMU_OPTION_paused, \
> > > > + "-paused [state=]postconf|preconf\n"
> > > > + " postconf: pause QEMU after machine is
> > > > initialized\n"
> > > > + " preconf: pause QEMU before machine is
> > > > initialized\n",
> > > > + QEMU_ARCH_ALL)
> > >
> > > I would like to allow pausing before machine-type is selected, so
> > > management could run query-machines before choosing a
> > > machine-type. Would that need a third "-pause" mode, or will we
> > > be able to change "preconf" to pause before select_machine() is
> > > called?
> > >
> > > The same probably applies to other things initialized before
> > > machine_run_board_init() that could be configurable using QMP,
> > > including but not limited to:
> > > * Accelerator configuration
> > > * Registering global properties
> > > * RAM size
> > > * SMP/CPU configuration
> >
> > Yeah.. having a bunch of different possible pause stages to select
> > doesn't sound great.
>
> I agree. The number of externally visible pause states should be
> as small as possible.
>
>
> > Could we avoid this by instead changing -S to
> > pause at the earliest possible spot, but having any monitor commands
> > that require a later stage automatically "fast forwarding" to the
> > right phase?
>
> That would hide the internal details from the outside. Sounds
> nice, but adding new machine/device configuration QMP commands
> while hiding the QEMU state from the outside sounds impossible.
>
> For example, if we use -S today, this works:
>
> $ qemu-system-x86_64 -S -qmp stdio
> <- {"QMP": {"version": {"qemu": {"micro": 0, "minor": 10, "major": 2},
> "package": " (v2.10.0-83-g9375da7831)"}, "capabilities": []}}
> -> {"execute":"qmp_capabilities"}
> <- {"return": {}}
> -> {"execute":"query-cpus"}
> <- {"return": [{"arch": "x86", "current": true, "props": {"core-id": 0,
> "thread-id": 0, "socket-id": 0}, "CPU": 0, "qom_path":
> "/machine/unattached/device[0]", "pc": 4294967280, "halted": false,
> "thread_id": 4038}]}
>
> This means "query-cpus" needs to fast-forward to the CPU creation
> stage if we want to keep compatibility.
>
> Now, assume we add a set-numa-node command like the one in this
> series. e.g.:
>
> $ qemu-system-x86_64 -S -qmp stdio
> <- {"QMP": {"version": {"qemu": {"micro": 0, "minor": 10, "major": 2},
> "package": " (v2.10.0-83-g9375da7831)"}, "capabilities": []}}
> -> {"execute":"qmp_capabilities"}
> <- {"return": {}}
> -> {"execute":"set-numa-node" ... }
> <- {"return": ...}
>
> The command will work only if machine initialization didn't run
> yet.
>
> But now an innocent-looking query command would change QEMU state
> in an unexpected way:
>
> $ qemu-system-x86_64 -S -qmp stdio
> <- {"QMP": {"version": {"qemu": {"micro": 0, "minor": 10, "major": 2},
> "package": " (v2.10.0-83-g9375da7831)"}, "capabilities": []}}
> -> {"execute":"qmp_capabilities"}
> <- {"return": {}}
> -> {"execute":"query-cpus"} [will silently fast-forward QEMU state]
> <- {"return": [{"arch": "x86", "current": true, "props": {"core-id": 0,
> "thread-id": 0, "socket-id": 0}, "CPU": 0, "qom_path":
> "/machine/unattached/device[0]", "pc": 4294967280, "halted": false,
> "thread_id": 4038}]}
> -> {"execute":"set-numa-node" ... }
> <- {"error": ...} [the command will fail because the machine was already
> created]
>
> This means we do have a externally visible "too late to use
> set-numa-node" QEMU state, and query-cpus will have a externally
> visible side effect. Every QMP command would need to document
> how it affects QEMU state in a externally visible way.
>
> If QEMU pause state is still going to be externally visible this
> way, I would prefer to let the client to explicitly tell what's
> the state they want QEMU to be, instead of making QEMU change
> state silently as a side effect of QMP commands.
Yeah, good point. My proposal would just have changed explicitly
exposed ugly internal state to subtly exposed ugly internal state,
which is probably worse :(.
Ok.. next possibly bad idea..
What about a "re-exec" monitor command; it would take what's
essentially a new command line, and basically restart qemu from the
beginning, reparsing this new command line, but without actually
Pro:
* Mitigates Daniel Berrange's concern about lots of qemu
configuration being buried in the qmp session - if libvirt logged
its last "re-exec" that would have what is generally needed.
* Lets libvirt do assorted investigation of options, then rewind to
choose what it actually wants
Con:
* Would require a bunch of auditing of structures/state to make sure
they can be re-initialized cleanly
* Would it be fast enough for libvirt to use? Do we know if the
slowness which makes multiple qemu invocations by libvirt
unattractive is from the kernel/libc/ldso overhead, or from qemu's
internal start up processing?
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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