[libvirt] [PATCH v2 2/2] qemu_process: detect updated video ram size values from QEMU

[Daniel P. Berrange]

On Fri, Jan 09, 2015 at 02:08:06PM +0100, Pavel Hrdina wrote:
> On 01/09/2015 10:51 AM, Daniel P. Berrange wrote:
> >On Fri, Jan 09, 2015 at 10:02:07AM +0100, Pavel Hrdina wrote:
> >>QEMU internally updates the size of video memory if the domain XML had
> >>provided too low memory size or there are some dependencies for a QXL
> >>devices 'vgamem' and 'ram' size. We need to know about the changes and
> >>store them into the status XML to not break migration or managedsave
> >>through different libvirt versions.
> >>
> >>Signed-off-by: Pavel Hrdina <phrdina at redhat.com>
> >>---
> >>  src/qemu/qemu_monitor.c      | 38 ++++++++++++++++++++++++
> >>  src/qemu/qemu_monitor.h      |  4 +++
> >>  src/qemu/qemu_monitor_json.c | 69 ++++++++++++++++++++++++++++++++++++++++++
> >>  src/qemu/qemu_monitor_json.h |  3 ++
> >>  src/qemu/qemu_process.c      | 71 ++++++++++++++++++++++++++++++++++++++++++++
> >>  5 files changed, 185 insertions(+)
> >>
> >>diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c
> >>index 55f07f3..45bb62f 100644
> >>--- a/src/qemu/qemu_monitor.c
> >>+++ b/src/qemu/qemu_monitor.c
> >>@@ -1154,6 +1154,44 @@ qemuMonitorFindBalloonObjectPath(qemuMonitorPtr mon,
> >>      return ret;
> >>  }
> >>
> >>+
> >>+/**
> >>+ * To update video memory size in status XML we need to load correct values from
> >>+ * QEMU.  This is supported only with JSON monitor.
> >>+ *
> >>+ * Returns 0 on success, -1 on failure and sets proper error message.
> >>+ */
> >>+int
> >>+qemuMonitorUpdateVideoMemorySize(qemuMonitorPtr mon,
> >>+                                 virDomainVideoDefPtr video,
> >>+                                 const char *videoName)
> >>+{
> >>+    int ret = -1;
> >>+    char *path = NULL;
> >>+
> >>+    if (mon->json) {
> >>+        if (qemuMonitorFindObjectPath(mon, "/", videoName, &path) < 0) {
> >>+            virReportError(VIR_ERR_INTERNAL_ERROR,
> >>+                           _("Failed to find QOM Object path for device '%s'"),
> >>+                           videoName);
> >>+            return -1;
> >>+        }
> >>+        if (qemuMonitorJSONUpdateVideoMemorySize(mon, video, path) < 0)
> >>+            goto cleanup;
> >>+    } else {
> >>+        virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
> >>+                       _("JSON monitor is required"));
> >>+        return -1;
> >>+    }
> >
> >This fatal error is going to break all guest startup with non-json
> >monitor IIUC.
> >
> >Regards,
> >Daniel
> >
> 
> Yes I know that. Should we return 0 and still reporting that error or should
> we just skip it at all if we cannot use mon-json?

We should silently skip this when json isn't available. That code path
will only happen on very old QEMU, which presumably won't suffer from
the bug you're trying to fix here.

Regards,
Daniel
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