@@ -15,6 +15,8 @@
/*
* Error reporting system loosely patterned after Glib's GError.
*
+ * = Creating errors =
+ *
* Create an error:
* error_setg(&err, "situation normal, all fouled up");
*
@@ -27,6 +29,8 @@
* error_setg(&err, "invalid quark\n" // WRONG!
* "Valid quarks are up, down, strange, charm, top, bottom.");
*
+ * = Reporting and destroying errors =
+ *
* Report an error to the current monitor if we have one, else stderr:
* error_report_err(err);
* This frees the error object.
@@ -40,6 +44,30 @@
* error_free(err);
* Note that this loses hints added with error_append_hint().
*
+ * Call a function ignoring errors:
+ * foo(arg, NULL);
+ * This is more concise than
+ * Error *err = NULL;
+ * foo(arg, &err);
+ * error_free(err); // don't do this
+ *
+ * Call a function aborting on errors:
+ * foo(arg, &error_abort);
+ * This is more concise and fails more nicely than
+ * Error *err = NULL;
+ * foo(arg, &err);
+ * assert(!err); // don't do this
+ *
+ * Call a function treating errors as fatal:
+ * foo(arg, &error_fatal);
+ * This is more concise than
+ * Error *err = NULL;
+ * foo(arg, &err);
+ * if (err) { // don't do this
+ * error_report_err(err);
+ * exit(1);
+ * }
+ *
* Handle an error without reporting it (just for completeness):
* error_free(err);
*
@@ -47,6 +75,11 @@
* reporting it (primarily useful in testsuites):
* error_free_or_abort(&err);
*
+ * = Passing errors around =
+ *
+ * Errors get passed to the caller through the conventional @errp
+ * parameter.
+ *
* Pass an existing error to the caller:
* error_propagate(errp, err);
* where Error **errp is a parameter, by convention the last one.
@@ -54,11 +87,10 @@
* Pass an existing error to the caller with the message modified:
* error_propagate_prepend(errp, err,
* "Could not frobnicate '%s': ", name);
- *
- * Avoid
- * error_propagate(errp, err);
+ * This is more concise than
+ * error_propagate(errp, err); // don't do this
* error_prepend(errp, "Could not frobnicate '%s': ", name);
- * because this fails to prepend when @errp is &error_fatal.
+ * and works even when @errp is &error_fatal.
*
* Create a new error and pass it to the caller:
* error_setg(errp, "situation normal, all fouled up");
@@ -70,15 +102,6 @@
* handle the error...
* }
*
- * Call a function ignoring errors:
- * foo(arg, NULL);
- *
- * Call a function aborting on errors:
- * foo(arg, &error_abort);
- *
- * Call a function treating errors as fatal:
- * foo(arg, &error_fatal);
- *
* Receive an error and pass it on to the caller:
* Error *err = NULL;
* foo(arg, &err);
@@ -86,8 +109,6 @@
* handle the error...
* error_propagate(errp, err);
* }
- * where Error **errp is a parameter, by convention the last one.
- *
* Do *not* "optimize" this to
* foo(arg, errp);
* if (*errp) { // WRONG!
Add headlines to the big comment. Explain examples for NULL, &error_abort and &error_fatal argument better. Tweak rationale for error_propagate_prepend(). Signed-off-by: Markus Armbruster <armbru@redhat.com> --- include/qapi/error.h | 51 +++++++++++++++++++++++++++++++------------- 1 file changed, 36 insertions(+), 15 deletions(-)