[PATCH v2 4/6] qemu-option: clean up id vs. list->merge_lists

[Paolo Bonzini <pbonzini@redhat.com>]

Forbid ids if the option is intended to be a singleton, as indicated by
list->merge_lists.  This avoids that "./qemu-system-x86_64 -M q35,id=ff"
uses a "pc" machine type.  Instead it errors out.  The affected options
are "qemu-img reopen -o", "qemu-io open -o", -rtc, -M, -boot, -name,
-m, -icount, -smp, -spice.

qemu_opts_create's fail_if_exists parameter is now unnecessary:

- it is unused if id is NULL

- opts_parse only passes false if reached from qemu_opts_set_defaults,
in which case this patch enforces that id must be NULL

- other callers that can pass a non-NULL id always set it to true

Assert that it is true in the only case where "fail_if_exists" matters,
i.e. "id && !lists->merge_lists".  This means that if an id is present,
duplicates are always forbidden, which was already the status quo.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 util/qemu-option.c | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/util/qemu-option.c b/util/qemu-option.c
index c88e159f18..91f4120ce1 100644
--- a/util/qemu-option.c
+++ b/util/qemu-option.c
@@ -619,7 +619,17 @@ QemuOpts *qemu_opts_create(QemuOptsList *list, const char *id,
 {
     QemuOpts *opts = NULL;
 
-    if (id) {
+    if (list->merge_lists) {
+        if (id) {
+            error_setg(errp, QERR_INVALID_PARAMETER, "id");
+            return NULL;
+        }
+        opts = qemu_opts_find(list, NULL);
+        if (opts) {
+            return opts;
+        }
+    } else if (id) {
+        assert(fail_if_exists);
         if (!id_wellformed(id)) {
             error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "id",
                        "an identifier");
@@ -629,17 +639,8 @@ QemuOpts *qemu_opts_create(QemuOptsList *list, const char *id,
         }
         opts = qemu_opts_find(list, id);
         if (opts != NULL) {
-            if (fail_if_exists && !list->merge_lists) {
-                error_setg(errp, "Duplicate ID '%s' for %s", id, list->name);
-                return NULL;
-            } else {
-                return opts;
-            }
-        }
-    } else if (list->merge_lists) {
-        opts = qemu_opts_find(list, NULL);
-        if (opts) {
-            return opts;
+            error_setg(errp, "Duplicate ID '%s' for %s", id, list->name);
+            return NULL;
         }
     }
     opts = g_malloc0(sizeof(*opts));
@@ -893,7 +894,7 @@ static QemuOpts *opts_parse(QemuOptsList *list, const char *params,
      * (if unlikely) future misuse:
      */
     assert(!defaults || list->merge_lists);
-    opts = qemu_opts_create(list, id, !defaults, errp);
+    opts = qemu_opts_create(list, id, !list->merge_lists, errp);
     g_free(id);
     if (opts == NULL) {
         return NULL;
-- 
2.26.2