xen: Use ERRP_GUARD()

If we want to check error after errp-function call, we need to
introduce local_err and then propagate it to errp. Instead, use
the ERRP_GUARD() macro, benefits are:
1. No need of explicit error_propagate call
2. No need of explicit local_err variable: use errp directly
3. ERRP_GUARD() leaves errp as is if it's not NULL or
   &error_fatal, this means that we don't break error_abort
   (we'll abort on error_set, not on error_propagate)

If we want to add some info to errp (by error_prepend() or
error_append_hint()), we must use the ERRP_GUARD() macro.
Otherwise, this info will not be added when errp == &error_fatal
(the program will exit prior to the error_append_hint() or
error_prepend() call).  No such cases are being fixed here.

This commit is generated by command

    sed -n '/^X86 Xen CPUs$/,/^$/{s/^F: //p}' MAINTAINERS | \
    xargs git ls-files | grep '\.[hc]$' | \
    xargs spatch \
        --sp-file scripts/coccinelle/errp-guard.cocci \
        --macro-file scripts/cocci-macro-file.h \
        --in-place --no-show-diff --max-width 80

Reported-by: Kevin Wolf <kwolf@redhat.com>
Reported-by: Greg Kurz <groug@kaod.org>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
[Commit message tweaked]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20200707165037.1026246-9-armbru@redhat.com>
[ERRP_AUTO_PROPAGATE() renamed to ERRP_GUARD(), and
auto-propagated-errp.cocci to errp-guard.cocci.  Commit message
tweaked again.]

1 files changed, 3 insertions, 4 deletions

diff --git a/hw/xen/xen-backend.c b/hw/xen/xen-backend.c
index da065f81b7..10199fb58d 100644
--- a/hw/xen/xen-backend.c
+++ b/hw/xen/xen-backend.c
@@ -98,9 +98,9 @@ static void xen_backend_list_remove(XenBackendInstance *backend)
 void xen_backend_device_create(XenBus *xenbus, const char *type,
                                const char *name, QDict *opts, Error **errp)
 {
+    ERRP_GUARD();
     const XenBackendImpl *impl = xen_backend_table_lookup(type);
     XenBackendInstance *backend;
-    Error *local_error = NULL;
 
     if (!impl) {
         return;
@@ -110,9 +110,8 @@ void xen_backend_device_create(XenBus *xenbus, const char *type,
     backend->xenbus = xenbus;
     backend->name = g_strdup(name);
 
-    impl->create(backend, opts, &local_error);
-    if (local_error) {
-        error_propagate(errp, local_error);
+    impl->create(backend, opts, errp);
+    if (*errp) {
         g_free(backend->name);
         g_free(backend);
         return;