error: Fix use of error_prepend() with &error_fatal, &error_abort
From include/qapi/error.h:
* Pass an existing error to the caller with the message modified:
* error_propagate(errp, err);
* error_prepend(errp, "Could not frobnicate '%s': ", name);
Fei Li pointed out that doing error_propagate() first doesn't work
well when @errp is &error_fatal or &error_abort: the error_prepend()
is never reached.
Since I doubt fixing the documentation will stop people from getting
it wrong, introduce error_propagate_prepend(), in the hope that it
lures people away from using its constituents in the wrong order.
Update the instructions in error.h accordingly.
Convert existing error_prepend() next to error_propagate to
error_propagate_prepend(). If any of these get reached with
&error_fatal or &error_abort, the error messages improve. I didn't
check whether that's the case anywhere.
Cc: Fei Li <fli@suse.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20181017082702.5581-2-armbru@redhat.com>
diff --git a/include/qapi/error.h b/include/qapi/error.h
index bcb86a7..51b63dd 100644
--- a/include/qapi/error.h
+++ b/include/qapi/error.h
@@ -52,8 +52,12 @@
* where Error **errp is a parameter, by convention the last one.
*
* Pass an existing error to the caller with the message modified:
+ * error_propagate_prepend(errp, err);
+ *
+ * Avoid
* error_propagate(errp, err);
* error_prepend(errp, "Could not frobnicate '%s': ", name);
+ * because this fails to prepend when @errp is &error_fatal.
*
* Create a new error and pass it to the caller:
* error_setg(errp, "situation normal, all fouled up");
@@ -215,6 +219,16 @@
*/
void error_propagate(Error **dst_errp, Error *local_err);
+
+/*
+ * Propagate error object (if any) with some text prepended.
+ * Behaves like
+ * error_prepend(&local_err, fmt, ...);
+ * error_propagate(dst_errp, local_err);
+ */
+void error_propagate_prepend(Error **dst_errp, Error *local_err,
+ const char *fmt, ...);
+
/*
* Prepend some text to @errp's human-readable error message.
* The text is made by formatting @fmt, @ap like vprintf().
