[libvirt] [PATCH] qemu-migration: Disallow migration of read only disk

[Corey S. McQuay]

Currently Libvirt allows attempts to migrate read only disks. Qemu cannot handle this as read only
disks cannot be written to on the destination system. The end result is a cryptic error message
and a failed migration.

This patch causes migration to fail earlier and provides a meaningful error message stating that
migrating read only disks is not supported.

Signed-off-by: Corey S. McQuay <csmcquay at linux.vnet.ibm.com>
Reviewed-by: Jason J. Herne <jjherne at linux.vnet.ibm.com>
Reviewed-by: Boris Fiuczynski <fiuczy at linux.vnet.ibm.com>
---
 src/qemu/qemu_migration.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c
index e451ef6..3311711 100644
--- a/src/qemu/qemu_migration.c
+++ b/src/qemu/qemu_migration.c
@@ -2392,6 +2392,28 @@ qemuMigrationIsSafe(virDomainDefPtr def,
     return true;
 }
 
+static bool
+qemuMigrationAreAllDisksRW(virDomainDefPtr def,
+                    size_t nmigrate_disks,
+                    const char **migrate_disks)
+{
+    size_t i;
+
+    for (i = 0; i < def->ndisks; i++) {
+        virDomainDiskDefPtr disk = def->disks[i];
+
+        if (qemuMigrateDisk(disk, nmigrate_disks, migrate_disks) &&
+            disk->src->readonly) {
+            virReportError(VIR_ERR_OPERATION_UNSUPPORTED,
+                       _("Cannot migrate read-only disk %s"),
+                       disk->dst);
+            return false;
+        }
+    }
+
+    return true;
+}
+
 /** qemuMigrationSetOffline
  * Pause domain for non-live migration.
  */
@@ -3137,6 +3159,9 @@ qemuMigrationBeginPhase(virQEMUDriverPtr driver,
         !qemuMigrationIsSafe(vm->def, nmigrate_disks, migrate_disks))
         goto cleanup;
 
+    if (!qemuMigrationAreAllDisksRW(vm->def, nmigrate_disks, migrate_disks))
+        goto cleanup;
+
     if (flags & VIR_MIGRATE_POSTCOPY &&
         (!(flags & VIR_MIGRATE_LIVE) ||
          flags & VIR_MIGRATE_PAUSED)) {
-- 
2.7.4