After setting a balloon target value, applications have to
continually poll 'query-balloon' to determine whether the
guest has reacted to this request. The virtio-balloon backend
knows exactly when the guest has reacted though, and thus it
is possible to emit a JSON event to tell the mgmt application
whenever the guest balloon changes.
This introduces a new 'qemu_balloon_changed()' API which is
to be called by balloon driver backends, whenever they have
a change in balloon value. This takes the 'actual' balloon
value, as would be found in the BalloonInfo struct.
The qemu_balloon_change API emits a JSON monitor event which
looks like:
{"timestamp": {"seconds": 1337162462, "microseconds": 814521},
"event": "BALLOON_CHANGE", "data": {"actual": 944766976}}
* balloon.c, balloon.h: Introduce qemu_balloon_changed() for
emitting balloon change events on the monitor
* hw/virtio-balloon.c: Invoke qemu_balloon_changed() whenever
the guest changes the balloon actual value
* monitor.c, monitor.h: Define QEVENT_BALLOON_CHANGE
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Acked-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Note that the command being dropped uses the deprecated MONITOR_CMD_ASYNC
API, but the new command is a regular synchronous command. There shouldn't
be visible differences though, as MONITOR_CMD_ASYNC is internal only.
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Please, note that some of the code supporting memory statistics is
still around (eg. virtio_balloon_receive_stats() and reset_stats()).
Also, the qmp_query_balloon() function is synchronous and thus doesn't
make any use of the (not fully working) monitor's asynchronous command
support (the old non-qapi implementation did).
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
When a balloon device gets unplugged, allow the balloon handlers to be
freed.
Reported-by: Shaolong Hu <shu@redhat.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Multiple balloon devices don't make sense; disallow more than one
registration attempt to register handlers.
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Passing on '0' as ballooning target to indicate retrieval of stats is
bad API. It also makes 'balloon 0' in the monitor cause a segfault.
Have two different functions handle the different functionality instead.
Detailed explanation from Markus's review:
1. do_info_balloon() is an info_async() method. It receives a callback
with argument, to be called exactly once (callback frees the
argument). It passes the callback via qemu_balloon_status() and
indirectly through qemu_balloon_event to virtio_balloon_to_target().
virtio_balloon_to_target() executes its balloon stats half. It
stores the callback in the device state.
If it can't send a stats request, it resets stats and calls the
callback right away.
Else, it sends a stats request. The device model runs the callback
when it receives the answer.
Works.
2. do_balloon() is a cmd_async() method. It receives a callback with
argument, to be called when the command completes. do_balloon()
calls it right before it succeeds. Odd, but should work.
Nevertheless, it passes the callback on via qemu_ballon() and
indirectly through qemu_balloon_event to virtio_balloon_to_target().
a. If the argument is non-zero, virtio_balloon_to_target() executes
its balloon half, which doesn't use the callback in any way.
Odd, but works.
b. If the argument is zero, virtio_balloon_to_target() executes its
balloon stats half, just like in 1. It either calls the callback
right away, or arranges for it to be called later.
Thus, the callback runs twice: use after free and double free.
Test case: start with -S -device virtio-balloon, execute "balloon 0" in
human monitor. Runs the callback first from virtio_balloon_to_target(),
then again from do_balloon().
Reported-by: Mike Cao <bcao@redhat.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
balloon.h had function declarations for a couple of functions that are
local to balloon.c. Make them static.
Drop the 'qemu_' prefix for balloon.c-local variables, and make them
static.
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
When using ballooning to manage overcommitted memory on a host, a system for
guests to communicate their memory usage to the host can provide information
that will minimize the impact of ballooning on the guests. The current method
employs a daemon running in each guest that communicates memory statistics to a
host daemon at a specified time interval. The host daemon aggregates this
information and inflates and/or deflates balloons according to the level of
host memory pressure. This approach is effective but overly complex since a
daemon must be installed inside each guest and coordinated to communicate with
the host. A simpler approach is to collect memory statistics in the virtio
balloon driver and communicate them directly to the hypervisor.
Signed-off-by: Adam Litke <agl@us.ibm.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
In the very least, a change like this requires discussion on the list.
The naming convention is goofy and it causes a massive merge problem. Something
like this _must_ be presented on the list first so people can provide input
and cope with it.
This reverts commit 99a0949b72.
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
