[libvirt] [PATCH] json: Avoid passing large positive 64 bit integers to QMP.

[Richard W.M. Jones]

We don't seem to be reaching any sort of sensible conclusion with qemu
about this bug, so it seems easier (albeit uglier) to fix it on the
libvirt side.

I have verified that with this patch virDomainMemoryPeek works on 64
bit guests.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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>From 9def1fb4a1b59b086493cf5eb78228515933e0b7 Mon Sep 17 00:00:00 2001
From: Richard W.M. Jones <rjones at redhat.com>
Date: Wed, 25 May 2011 17:52:26 +0100
Subject: [PATCH] json: Avoid passing large positive 64 bit integers to QMP.

http://lists.gnu.org/archive/html/qemu-devel/2011-05/threads.html#02162

Currently, qemu silently clips any JSON integer in the range
0x8000000000000000 - 0xffffffffffffffff (all numbers in this range
will be clipped to 0x7fffffffffffffff == LLONG_MAX).

To avoid this, pass these as signed 64 bit integers in the QMP
request.
---
 src/qemu/qemu_monitor_json.c |    9 +++++++--
 1 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/qemu/qemu_monitor_json.c b/src/qemu/qemu_monitor_json.c
index 2d8a390..bdd0dcb 100644
--- a/src/qemu/qemu_monitor_json.c
+++ b/src/qemu/qemu_monitor_json.c
@@ -413,8 +413,13 @@ qemuMonitorJSONMakeCommand(const char *cmdname,
             ret = virJSONValueObjectAppendNumberLong(jargs, key, val);
         }   break;
         case 'U': {
-            unsigned long long val = va_arg(args, unsigned long long);
-            ret = virJSONValueObjectAppendNumberUlong(jargs, key, val);
+            /* qemu silently truncates numbers larger than LLONG_MAX,
+             * so passing the full range of unsigned 64 bit integers
+             * is not safe here.  Pass them as signed 64 bit integers
+             * instead.
+             */
+            long long val = va_arg(args, long long);
+            ret = virJSONValueObjectAppendNumberLong(jargs, key, val);
         }   break;
         case 'd': {
             double val = va_arg(args, double);
-- 
1.7.5.1