chardev: add support for qapi-based chardev initialization

This patch add support for a new way to initialize chardev devices.
Instead of calling a initialization function with a QemuOpts we will
now create a (qapi) ChardevBackend, optionally call a function to
fill ChardevBackend from QemuOpts, then go create the chardev using
the new qapi code path which is also used by chardev-add.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

include/char/char.h

@@ -245,6 +245,8 @@ CharDriverState *qemu_chr_find(const char *name);
 QemuOpts *qemu_chr_parse_compat(const char *label, const char *filename);
 
 void register_char_driver(const char *name, CharDriverState *(*open)(QemuOpts *));
+void register_char_driver_qapi(const char *name, int kind,
+        void (*parse)(QemuOpts *opts, ChardevBackend *backend, Error **errp));
 
 /* add an eventfd to the qemu devices that are polled */
 CharDriverState *qemu_chr_open_eventfd(int eventfd);

qemu-char.c

@@ -3204,7 +3204,11 @@ static CharDriverState *qemu_chr_open_pp(QemuOpts *opts)
 
 typedef struct CharDriver {
     const char *name;
+    /* old, pre qapi */
     CharDriverState *(*open)(QemuOpts *opts);
+    /* new, qapi-based */
+    int kind;
+    void (*parse)(QemuOpts *opts, ChardevBackend *backend, Error **errp);
 } CharDriver;
 
 static GSList *backends;
@@ -3220,6 +3224,19 @@ void register_char_driver(const char *name, CharDriverState *(*open)(QemuOpts *)
     backends = g_slist_append(backends, s);
 }
 
+void register_char_driver_qapi(const char *name, int kind,
+        void (*parse)(QemuOpts *opts, ChardevBackend *backend, Error **errp))
+{
+    CharDriver *s;
+
+    s = g_malloc0(sizeof(*s));
+    s->name = g_strdup(name);
+    s->kind = kind;
+    s->parse = parse;
+
+    backends = g_slist_append(backends, s);
+}
+
 CharDriverState *qemu_chr_new_from_opts(QemuOpts *opts,
                                     void (*init)(struct CharDriverState *s),
                                     Error **errp)
@@ -3251,6 +3268,32 @@ CharDriverState *qemu_chr_new_from_opts(QemuOpts *opts,
         return NULL;
     }
 
+    if (!cd->open) {
+        /* using new, qapi init */
+        ChardevBackend *backend = g_new0(ChardevBackend, 1);
+        ChardevReturn *ret = NULL;
+        const char *id = qemu_opts_id(opts);
+
+        chr = NULL;
+        backend->kind = cd->kind;
+        if (cd->parse) {
+            cd->parse(opts, backend, errp);
+            if (error_is_set(errp)) {
+                goto qapi_out;
+            }
+        }
+        ret = qmp_chardev_add(qemu_opts_id(opts), backend, errp);
+        if (error_is_set(errp)) {
+            goto qapi_out;
+        }
+        chr = qemu_chr_find(id);
+
+    qapi_out:
+        qapi_free_ChardevBackend(backend);
+        qapi_free_ChardevReturn(ret);
+        return chr;
+    }
+
     chr = cd->open(opts);
     if (!chr) {
         error_setg(errp, "chardev: opening backend \"%s\" failed",