[Qemu-devel] [PATCH v2 1/2] 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 omit the tls_creds parameter in migrate-set-parameters,
then 'has_tls_creds' will be false and so no action will be taken. JSON
allows a parameter to have a nil value, but the QEMU JSON visitor will
reject that when deserializing into a QObject.

The migration code has no need to distinguish "" vs NULL for the TLS
hostname or TLS credentials object name, since "" is invalid in both
cases. This enables clearing of tls-hostname and tls-creds by
treating "" as equivalent to NULL.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---
 migration/migration.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/migration/migration.c b/migration/migration.c
index c6ae69d..a8cb56e 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_hostname == '\0') {
+            s->parameters.tls_hostname = 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