qemu-option: restrict qemu_opts_set to merge-lists QemuOpts

qemu_opts_set is used to create default network backends and to
parse sugar options -kernel, -initrd, -append, -bios and -dtb.
These are very different uses:

I would *expect* a function named qemu_opts_set to set an option in a
merge-lists QemuOptsList, such as -kernel, and possibly to set an option
in a non-merge-lists QemuOptsList with non-NULL id, similar to -set.

However, it wouldn't *work* to use qemu_opts_set for the latter
because qemu_opts_set uses fail_if_exists==1. So, for non-merge-lists
QemuOptsList and non-NULL id, the semantics of qemu_opts_set (fail if the
(QemuOptsList, id) pair already exists) are debatable.

On the other hand, I would not expect qemu_opts_set to create a
non-merge-lists QemuOpts with a single option; which it does, though.
For this case of non-merge-lists QemuOptsList and NULL id, qemu_opts_set
hardly adds value over qemu_opts_parse.  It does skip some parsing and
unescaping, but that's not needed when creating default network
backends.

So qemu_opts_set has warty behavior for non-merge-lists QemuOptsList
if id is non-NULL, and it's mostly pointless if id is NULL.  My
solution to keeping the API as simple as possible is to limit
qemu_opts_set to merge-lists QemuOptsList.  For them, it's useful (we
don't want comma-unescaping for -kernel) *and* has sane semantics.
Network backend creation is switched to qemu_opts_parse.

qemu_opts_set is now only used on merge-lists QemuOptsList... except
in the testcase, which is changed to use a merge-list QemuOptsList.

With this change we can also remove the id parameter.  With the
parameter always NULL, we know that qemu_opts_create cannot fail
and can pass &error_abort to it.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/qemu/option.h

@@ -119,8 +119,7 @@ QemuOpts *qemu_opts_create(QemuOptsList *list, const char *id,
                            int fail_if_exists, Error **errp);
 void qemu_opts_reset(QemuOptsList *list);
 void qemu_opts_loc_restore(QemuOpts *opts);
-bool qemu_opts_set(QemuOptsList *list, const char *id,
-                   const char *name, const char *value, Error **errp);
+bool qemu_opts_set(QemuOptsList *list, const char *name, const char *value, Error **errp);
 const char *qemu_opts_id(QemuOpts *opts);
 void qemu_opts_set_id(QemuOpts *opts, char *id);
 void qemu_opts_del(QemuOpts *opts);

softmmu/vl.c

@@ -3388,20 +3388,16 @@ void qemu_init(int argc, char **argv, char **envp)
                 }
                 break;
             case QEMU_OPTION_kernel:
-                qemu_opts_set(qemu_find_opts("machine"), NULL, "kernel", optarg,
-                              &error_abort);
+                qemu_opts_set(qemu_find_opts("machine"), "kernel", optarg, &error_abort);
                 break;
             case QEMU_OPTION_initrd:
-                qemu_opts_set(qemu_find_opts("machine"), NULL, "initrd", optarg,
-                              &error_abort);
+                qemu_opts_set(qemu_find_opts("machine"), "initrd", optarg, &error_abort);
                 break;
             case QEMU_OPTION_append:
-                qemu_opts_set(qemu_find_opts("machine"), NULL, "append", optarg,
-                              &error_abort);
+                qemu_opts_set(qemu_find_opts("machine"), "append", optarg, &error_abort);
                 break;
             case QEMU_OPTION_dtb:
-                qemu_opts_set(qemu_find_opts("machine"), NULL, "dtb", optarg,
-                              &error_abort);
+                qemu_opts_set(qemu_find_opts("machine"), "dtb", optarg, &error_abort);
                 break;
             case QEMU_OPTION_cdrom:
                 drive_add(IF_DEFAULT, 2, optarg, CDROM_OPTS);
@@ -3511,8 +3507,7 @@ void qemu_init(int argc, char **argv, char **envp)
                 }
                 break;
             case QEMU_OPTION_bios:
-                qemu_opts_set(qemu_find_opts("machine"), NULL, "firmware", optarg,
-                              &error_abort);
+                qemu_opts_set(qemu_find_opts("machine"), "firmware", optarg, &error_abort);
                 break;
             case QEMU_OPTION_singlestep:
                 singlestep = 1;
@@ -4395,9 +4390,9 @@ void qemu_init(int argc, char **argv, char **envp)
 
     if (default_net) {
         QemuOptsList *net = qemu_find_opts("net");
-        qemu_opts_set(net, NULL, "type", "nic", &error_abort);
+        qemu_opts_parse(net, "nic", true, &error_abort);
 #ifdef CONFIG_SLIRP
-        qemu_opts_set(net, NULL, "type", "user", &error_abort);
+        qemu_opts_parse(net, "user", true, &error_abort);
 #endif
     }
 

tests/test-qemu-opts.c

@@ -84,11 +84,25 @@ static QemuOptsList opts_list_03 = {
     },
 };
 
+static QemuOptsList opts_list_04 = {
+    .name = "opts_list_04",
+    .head = QTAILQ_HEAD_INITIALIZER(opts_list_04.head),
+    .merge_lists = true,
+    .desc = {
+        {
+            .name = "str3",
+            .type = QEMU_OPT_STRING,
+        },
+        { /* end of list */ }
+    },
+};
+
 static void register_opts(void)
 {
     qemu_add_opts(&opts_list_01);
     qemu_add_opts(&opts_list_02);
     qemu_add_opts(&opts_list_03);
+    qemu_add_opts(&opts_list_04);
 }
 
 static void test_find_unknown_opts(void)
@@ -402,17 +416,17 @@ static void test_qemu_opts_set(void)
     QemuOpts *opts;
     const char *opt;
 
-    list = qemu_find_opts("opts_list_01");
+    list = qemu_find_opts("opts_list_04");
     g_assert(list != NULL);
     g_assert(QTAILQ_EMPTY(&list->head));
-    g_assert_cmpstr(list->name, ==, "opts_list_01");
+    g_assert_cmpstr(list->name, ==, "opts_list_04");
 
     /* should not find anything at this point */
     opts = qemu_opts_find(list, NULL);
     g_assert(opts == NULL);
 
     /* implicitly create opts and set str3 value */
-    qemu_opts_set(list, NULL, "str3", "value", &error_abort);
+    qemu_opts_set(list, "str3", "value", &error_abort);
     g_assert(!QTAILQ_EMPTY(&list->head));
 
     /* get the just created opts */

util/qemu-option.c

@@ -670,15 +670,12 @@ void qemu_opts_loc_restore(QemuOpts *opts)
     loc_restore(&opts->loc);
 }
 
-bool qemu_opts_set(QemuOptsList *list, const char *id,
-                   const char *name, const char *value, Error **errp)
+bool qemu_opts_set(QemuOptsList *list, const char *name, const char *value, Error **errp)
 {
     QemuOpts *opts;
 
-    opts = qemu_opts_create(list, id, 1, errp);
-    if (!opts) {
-        return false;
-    }
+    assert(list->merge_lists);
+    opts = qemu_opts_create(list, NULL, 0, &error_abort);
     return qemu_opt_set(opts, name, value, errp);
 }