[PATCH v3] qemu-migration: Disallow migration of read only disk

["Corey S. McQuay" <csmcquay@xxxxxxxxxxxxxxxxxx>]

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@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Jason J. Herne <jjherne@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Boris Fiuczynski <fiuczy@xxxxxxxxxxxxxxxxxx>
---
 src/qemu/qemu_migration.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c
index e451ef6..c8fb7ec 100644
--- a/src/qemu/qemu_migration.c
+++ b/src/qemu/qemu_migration.c
@@ -1764,6 +1764,12 @@ qemuMigrationStartNBDServer(virQEMUDriverPtr driver,
         /* check whether disk should be migrated */
         if (!qemuMigrateDisk(disk, nmigrate_disks, migrate_disks))
             continue;
+            
+        if (disk->src->readonly) {
+            virReportError(VIR_ERR_OPERATION_UNSUPPORTED, 
+                        _("Cannot migrate read-only disk %s"), disk->dst);
+            goto cleanup;
+        }
 
         VIR_FREE(diskAlias);
         if (!(diskAlias = qemuAliasFromDisk(disk)))
-- 
2.7.4

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