char: Clean up fragile use of error_is_set()

Using error_is_set(ERRP) to find out whether a function failed is
either wrong, fragile, or unnecessarily opaque.  It's wrong when ERRP
may be null, because errors go undetected when it is.  It's fragile
when proving ERRP non-null involves a non-local argument.  Else, it's
unnecessarily opaque (see commit 84d18f0).

The error_is_set(errp) in qemu_chr_new_from_opts() is merely fragile,
because the callers never pass a null errp argument.

Make the code more robust and more obviously correct: receive the
error in a local variable, then propagate it through the parameter.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/qemu-char.c b/qemu-char.c
index 3eaefc9244..5a7975f393 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -3204,6 +3204,7 @@ CharDriverState *qemu_chr_new_from_opts(QemuOpts *opts,
                                     void (*init)(struct CharDriverState *s),
                                     Error **errp)
 {
+    Error *local_err = NULL;
     CharDriver *cd;
     CharDriverState *chr;
     GSList *i;
@@ -3245,8 +3246,9 @@ CharDriverState *qemu_chr_new_from_opts(QemuOpts *opts,
         chr = NULL;
         backend->kind = cd->kind;
         if (cd->parse) {
-            cd->parse(opts, backend, errp);
-            if (error_is_set(errp)) {
+            cd->parse(opts, backend, &local_err);
+            if (local_err) {
+                error_propagate(errp, local_err);
                 goto qapi_out;
             }
         }