[Qemu-devel] [RFC PATCH v1 05/25] error: Add error prefix API

[Peter Crosthwaite]

Add an API to prefix an already set error with a caller-centric
message.

If multiple errors are set, all are prefixed individually.

Signed-off-by: Peter Crosthwaite <address@hidden>
---

 include/qapi/error.h |  6 ++++++
 util/error.c         | 26 ++++++++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/include/qapi/error.h b/include/qapi/error.h
index f44c451..b25c72f 100644
--- a/include/qapi/error.h
+++ b/include/qapi/error.h
@@ -78,6 +78,12 @@ ErrorClass error_get_class(const Error *err);
 Error *error_copy(const Error *err);
 
 /**
+ * Prefix an error message with a formatted string.
+ */
+
+void error_prefix(Error *err, const char *fmt, ...);
+
+/**
  * Get a human readable representation of an error object.
  */
 const char *error_get_pretty(Error *err);
diff --git a/util/error.c b/util/error.c
index 890ce58..e9c23ce 100644
--- a/util/error.c
+++ b/util/error.c
@@ -19,6 +19,7 @@ struct Error
     char *msg;
     ErrorClass err_class;
     struct Error *next;
+    bool prefixed;
 };
 
 Error *error_abort;
@@ -142,6 +143,26 @@ const char *error_get_pretty(Error *err)
     return err->msg;
 }
 
+void error_prefix(Error *err, const char *fmt, ...) {
+    char *msg;
+    char *fmt_full;
+    va_list ap;
+
+    if (!err || err->prefixed) {
+        return;
+    }
+    err->prefixed = true;
+
+    msg = err->msg;
+    fmt_full =  g_strdup_printf("%s%%s", fmt);
+
+    va_start(ap, fmt);
+    err->msg = g_strdup_printf(fmt_full, ap, msg);
+    va_end(ap);
+    g_free(fmt_full);
+    g_free(msg);
+}
+
 void error_report_err(Error *err)
 {
     error_report("%s", error_get_pretty(err));
@@ -170,6 +191,11 @@ void error_propagate(Error **dst_errp, Error *local_err)
 
         *dst_errp = local_err;
         for (i = local_err; i; i = i->next) {
+            /* Propagation implies that the caller is no longer the owner of 
the
+             * error. Therefore reset prefixes, so higher level handlers can
+             * prefix again.
+             */
+            i->prefixed = false;
             dst_errp = &i->next;
         }
         *dst_errp = old_dst_err;
-- 
1.9.1