chardev: give some context on chardev-add error

Description from Daniel P. Berrangé:
> The original code reported:
>
>  "attempt to add duplicate property 'char2' to object (type 'container')"
>
> Since adding yank support, the current code reports
>
>  "duplicate yank instance"
>
> With this patch applied it now reports:
>
>  "Failed to add chardev 'char2': duplicate yank instance"
>
> This is marginally better, but still not great, not that the original
> error was great either.
>
> It would be nice if we could report
>
>   "chardev with id 'char2' already exists"

Related to:
https://bugzilla.redhat.com/show_bug.cgi?id=1984721

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

1 files changed, 9 insertions, 6 deletions

diff --git a/chardev/char.c b/chardev/char.c
index d959eec522..f59a61774b 100644
--- a/chardev/char.c
+++ b/chardev/char.c
@@ -1031,27 +1031,26 @@ Chardev *qemu_chardev_new(const char *id, const char *typename,
 ChardevReturn *qmp_chardev_add(const char *id, ChardevBackend *backend,
                                Error **errp)
 {
+    ERRP_GUARD();
     const ChardevClass *cc;
     ChardevReturn *ret;
-    Chardev *chr;
+    g_autoptr(Chardev) chr = NULL;
 
     cc = char_get_class(ChardevBackendKind_str(backend->type), errp);
     if (!cc) {
-        return NULL;
+        goto err;
     }
 
     chr = chardev_new(id, object_class_get_name(OBJECT_CLASS(cc)),
                       backend, NULL, false, errp);
     if (!chr) {
-        return NULL;
+        goto err;
     }
 
     if (!object_property_try_add_child(get_chardevs_root(), id, OBJECT(chr),
                                        errp)) {
-        object_unref(OBJECT(chr));
-        return NULL;
+        goto err;
     }
-    object_unref(OBJECT(chr));
 
     ret = g_new0(ChardevReturn, 1);
     if (CHARDEV_IS_PTY(chr)) {
@@ -1060,6 +1059,10 @@ ChardevReturn *qmp_chardev_add(const char *id, ChardevBackend *backend,
     }
 
     return ret;
+
+err:
+    error_prepend(errp, "Failed to add chardev '%s': ", id);
+    return NULL;
 }
 
 ChardevReturn *qmp_chardev_change(const char *id, ChardevBackend *backend,