[libvirt] [PATCH 2/4] qemu: process: detect if dimm aliases are broken on reconnect

[Peter Krempa]

Detect on reconnect to a running qemu VM whether the alias of a
hotpluggable memory device (dimm) does not match the dimm slot number
where it's connected to. This is necessary as qemu is actually
considering the alias as machine ABI used to connect the backend object
to the dimm device.

This will require us to keep them consistent so that we can reliably
restore them on migration. In some situations it was currently possible
to create a mismatched configuration and qemu would refuse to restore
the migration stream.

To avoid breaking existing VMs we'll need to keep the old algorithm
though.
---
 src/qemu/qemu_domain.h  |  3 +++
 src/qemu/qemu_process.c | 25 +++++++++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/src/qemu/qemu_domain.h b/src/qemu/qemu_domain.h
index 2ee1829..1b7b375 100644
--- a/src/qemu/qemu_domain.h
+++ b/src/qemu/qemu_domain.h
@@ -232,6 +232,9 @@ struct _qemuDomainObjPrivate {
     /* private XML) - need to restore at process reconnect */
     uint8_t *masterKey;
     size_t masterKeyLen;
+
+    /* note whether memory device alias does not correspond to slot number */
+    bool memHotplugAliasMismatch;
 };

 # define QEMU_DOMAIN_PRIVATE(vm)	\
diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index 1b67aee..15b8ec8 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -3205,6 +3205,29 @@ qemuDomainPerfRestart(virDomainObjPtr vm)
     return 0;
 }

+
+static void
+qemuProcessReconnectCheckMemoryHotplugMismatch(virDomainObjPtr vm)
+{
+    size_t i;
+    int aliasidx;
+    virDomainDefPtr def = vm->def;
+    qemuDomainObjPrivatePtr priv = vm->privateData;
+
+    if (!virDomainDefHasMemoryHotplug(def) || def->nmems == 0)
+        return;
+
+    for (i = 0; i < def->nmems; i++) {
+        aliasidx = qemuDomainDeviceAliasIndex(&def->mems[i]->info, "dimm");
+
+        if (def->mems[i]->info.addr.dimm.slot != aliasidx) {
+            priv->memHotplugAliasMismatch = true;
+            break;
+        }
+    }
+}
+
+
 struct qemuProcessReconnectData {
     virConnectPtr conn;
     virQEMUDriverPtr driver;
@@ -3389,6 +3412,8 @@ qemuProcessReconnect(void *opaque)
     if (qemuProcessUpdateDevices(driver, obj) < 0)
         goto error;

+    qemuProcessReconnectCheckMemoryHotplugMismatch(obj);
+
     /* Failure to connect to agent shouldn't be fatal */
     if ((ret = qemuConnectAgent(driver, obj)) < 0) {
         if (ret == -2)
-- 
2.10.2