[Qemu-devel] [PATCH] migration: allow clearing migration string parameters

["Daniel P. Berrange" <berrange@redhat.com>]

Some of the migration parameters are strings, which default to NULL,
eg tls_hostname and tls_creds.

The mgmt app will set the tls_creds parameter on both source and target
QEMU instances, in order to trigger use of TLS for migration.

After performing a TLS encrypted migration though, migration might be
used for other reasons - for example, to save the QEMU state to a file.
We need TLS turned off when doing this, but the migrate-set-parameters
QAPI command does not provide any facility to clear/reset parameters
to their default state.

If you simply ommit the tls_creds parameter in migrate-set-parameters,
then 'has_tls_creds' will be false and so no action will be taken. The
only option that works with migrate-set-parameters is to treat "" on
the wire as equivalent to requesting NULL. Failing that we would have
to create a new 'migrate-reset-parameters' method to explicitly put
a parameter back to its default value.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---

CC'ing Eric & Markus since this is related to QAPI schema for migrate
monitor commands

 migration/migration.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/migration/migration.c b/migration/migration.c
index c6ae69d..a5d41a9 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -872,11 +872,19 @@ void qmp_migrate_set_parameters(MigrationParameters *params, Error **errp)
     }
     if (params->has_tls_creds) {
         g_free(s->parameters.tls_creds);
-        s->parameters.tls_creds = g_strdup(params->tls_creds);
+        if (*params->tls_creds == '\0') {
+            s->parameters.tls_creds = NULL;
+        } else {
+            s->parameters.tls_creds = g_strdup(params->tls_creds);
+        }
     }
     if (params->has_tls_hostname) {
         g_free(s->parameters.tls_hostname);
-        s->parameters.tls_hostname = g_strdup(params->tls_hostname);
+        if (*params->tls_hostnane == '\0') {
+            s->parameters.tls_hostnane = NULL;
+        } else {
+            s->parameters.tls_hostname = g_strdup(params->tls_hostname);
+        }
     }
     if (params->has_max_bandwidth) {
         s->parameters.max_bandwidth = params->max_bandwidth;
-- 
2.9.3