[PATCHv2 2/2] conf: allow fuzz in XML with cur balloon > max

[Eric Blake <eblake@xxxxxxxxxx>]

Commit 1b1402b introduced a regression.  Since older libvirt versions
would silently round memory up (until the previous patch), but populated
current memory based on querying the guest, it was possible to have
current > maximum by the amount of the rounding.  Accept this fuzz
factor, and silently clamp current down to maximum in that case,
rather than failing to reparse XML for an existing VM.

* src/conf/domain_conf.c (virDomainDefParseXML): Don't reject
existing XML.
Based on a report by Zhou Peng.
---
 src/conf/domain_conf.c       |   19 +++++++++++++++----
 src/qemu/qemu_monitor_json.c |    2 +-
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index 4caef6f..7c95920 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -7776,10 +7776,21 @@ static virDomainDefPtr virDomainDefParseXML(virCapsPtr caps,
         goto error;

     if (def->mem.cur_balloon > def->mem.max_balloon) {
-        virDomainReportError(VIR_ERR_XML_ERROR,
-                             _("current memory '%lluk' exceeds maximum '%lluk'"),
-                             def->mem.cur_balloon, def->mem.max_balloon);
-        goto error;
+        /* Older libvirt could get into this situation due to
+         * rounding; if the discrepancy is less than 1MiB, we silently
+         * round down, otherwise we flag the issue.  */
+        if (VIR_DIV_UP(def->mem.cur_balloon, 1024) >
+            VIR_DIV_UP(def->mem.max_balloon, 1024)) {
+            virDomainReportError(VIR_ERR_XML_ERROR,
+                                 _("current memory '%lluk' exceeds "
+                                   "maximum '%lluk'"),
+                                 def->mem.cur_balloon, def->mem.max_balloon);
+            goto error;
+        } else {
+            VIR_DEBUG("Truncating current %lluk to maximum %lluk",
+                      def->mem.cur_balloon, def->mem.max_balloon);
+            def->mem.cur_balloon = def->mem.max_balloon;
+        }
     } else if (def->mem.cur_balloon == 0) {
         def->mem.cur_balloon = def->mem.max_balloon;
     }
diff --git a/src/qemu/qemu_monitor_json.c b/src/qemu/qemu_monitor_json.c
index 7093e1d..6d66587 100644
--- a/src/qemu/qemu_monitor_json.c
+++ b/src/qemu/qemu_monitor_json.c
@@ -2022,7 +2022,7 @@ int qemuMonitorJSONSetBalloon(qemuMonitorPtr mon,
 {
     int ret;
     virJSONValuePtr cmd = qemuMonitorJSONMakeCommand("balloon",
-                                                     "U:value", ((unsigned long long)newmem)*1024,
+                                                     "U:value", newmem*1024ULL,
                                                      NULL);
     virJSONValuePtr reply = NULL;
     if (!cmd)
-- 
1.7.1

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