migration: Simplify initial conditionals in migration for better read…

…ability

The inital conditional statements in qmp migration functions is harder
to understand than necessary. It is better to get all errors out of
the way in the beginning itself to have better readability and error
handling.

Signed-off-by: Het Gala <het.gala@nutanix.com>
Suggested-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20231205080039.197615-1-het.gala@nutanix.com
Signed-off-by: Peter Xu <peterx@redhat.com>

migration/migration.c

@@ -523,28 +523,26 @@ static void qemu_start_incoming_migration(const char *uri, bool has_channels,
     /*
      * Having preliminary checks for uri and channel
      */
-    if (uri && has_channels) {
-        error_setg(errp, "'uri' and 'channels' arguments are mutually "
-                   "exclusive; exactly one of the two should be present in "
-                   "'migrate-incoming' qmp command ");
+    if (!uri == !channels) {
+        error_setg(errp, "need either 'uri' or 'channels' argument");
         return;
-    } else if (channels) {
+    }
+
+    if (channels) {
         /* To verify that Migrate channel list has only item */
         if (channels->next) {
             error_setg(errp, "Channel list has more than one entries");
             return;
         }
         addr = channels->value->addr;
-    } else if (uri) {
+    }
+
+    if (uri) {
         /* caller uses the old URI syntax */
         if (!migrate_uri_parse(uri, &channel, errp)) {
             return;
         }
         addr = channel->addr;
-    } else {
-        error_setg(errp, "neither 'uri' or 'channels' argument are "
-                   "specified in 'migrate-incoming' qmp command ");
-        return;
     }
 
     /* transport mechanism not suitable for migration? */
@@ -1924,28 +1922,26 @@ void qmp_migrate(const char *uri, bool has_channels,
     /*
      * Having preliminary checks for uri and channel
      */
-    if (uri && has_channels) {
-        error_setg(errp, "'uri' and 'channels' arguments are mutually "
-                   "exclusive; exactly one of the two should be present in "
-                   "'migrate' qmp command ");
+    if (!uri == !channels) {
+        error_setg(errp, "need either 'uri' or 'channels' argument");
         return;
-    } else if (channels) {
+    }
+
+    if (channels) {
         /* To verify that Migrate channel list has only item */
         if (channels->next) {
             error_setg(errp, "Channel list has more than one entries");
             return;
         }
         addr = channels->value->addr;
-    } else if (uri) {
+    }
+
+    if (uri) {
         /* caller uses the old URI syntax */
         if (!migrate_uri_parse(uri, &channel, errp)) {
             return;
         }
         addr = channel->addr;
-    } else {
-        error_setg(errp, "neither 'uri' or 'channels' argument are "
-                   "specified in 'migrate' qmp command ");
-        return;
     }
 
     /* transport mechanism not suitable for migration? */