[Qemu-devel] [PATCH 0/6] QMP: add balloon-get-memory-stats command

[Luiz Capitulino <lcapitulino@redhat.com>]

This series re-enables the balloon memory statistics feature disabled
long ago by commit 11724ff.

The feature has been disabled because it added a severe bug: query-balloon
would hang if the guest didn't respond. This, in turn, would also cause a
hang in libvirt.

To avoid that bug, the solution implemented in this series uses a command
and an event. The command gets the process started by sending a request to
guest and returns. Later, when the guest makes the memory stats info
available, it's sent to the client by means of an QMP event (please, take a
look at patch 6/6 for full details).

This series has an issue though: it lacks HMP support. The reason for this
is that there's no way to wait for an event in HMP. There are two ways to
solve this:

 1. We wait to have support for events in the QAPI. This way it will be
    possible to wait for events from HMP

 2. Add a query-balloon-memory-stats command which polls for the guest
    response (and immediatelly returns if the guest response is not
    available)

I'm going on only with the event for now, as this is slightly simpler.

 QMP/qmp-events.txt  |   36 ++++++++++++++++++++++++
 balloon.c           |   61 +++++++++++++++++++++++++++++++---------
 balloon.h           |    7 +++--
 hmp.c               |   25 +----------------
 hw/virtio-balloon.c |   76 ++++++++++++++++++++++++++++++++++-----------------
 monitor.c           |    2 +
 monitor.h           |    1 +
 qapi-schema.json    |   42 +++++++++++++++-------------
 qmp-commands.hx     |    5 +++
 9 files changed, 169 insertions(+), 86 deletions(-)