block/nbd: Add nbd_has_filename_options_conflict()

Right now, we have four possible options that conflict with specifying
an NBD filename, and a future patch will add another one ("address").
This future option is a nested QDict that is flattened at this point,
requiring us to test each option whether its key has an "address."
prefix. Therefore, we will then need to iterate through all options
(including the "export" option which was not covered so far).

Adding this iteration logic now will simplify adding the new option
later. A nice side effect is that the user will not receive a long list
of five options which are not supposed to be specified with a filename,
but we can actually print the problematic option.
Reviewed-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/nbd.c

@@ -123,6 +123,25 @@ out:
     return ret;
 }
 
+static bool nbd_has_filename_options_conflict(QDict *options, Error **errp)
+{
+    const QDictEntry *e;
+
+    for (e = qdict_first(options); e; e = qdict_next(options, e)) {
+        if (!strcmp(e->key, "host") ||
+            !strcmp(e->key, "port") ||
+            !strcmp(e->key, "path") ||
+            !strcmp(e->key, "export"))
+        {
+            error_setg(errp, "Option '%s' cannot be used with a file name",
+                       e->key);
+            return true;
+        }
+    }
+
+    return false;
+}
+
 static void nbd_parse_filename(const char *filename, QDict *options,
                                Error **errp)
 {
@@ -131,12 +150,7 @@ static void nbd_parse_filename(const char *filename, QDict *options,
     const char *host_spec;
     const char *unixpath;
 
-    if (qdict_haskey(options, "host")
-        || qdict_haskey(options, "port")
-        || qdict_haskey(options, "path"))
-    {
-        error_setg(errp, "host/port/path and a file name may not be specified "
-                         "at the same time");
+    if (nbd_has_filename_options_conflict(options, errp)) {
         return;
     }