From b41fc6d57fae80ac2a431bca22862985f003fe88 Mon Sep 17 00:00:00 2001

From: =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= <marcandre.lureau@redhat.com>

Date: Fri, 8 Jan 2021 07:40:54 -0500

Subject: [PATCH 03/10] error: Improve error.h's big comment

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RH-Author: Marc-André Lureau <marcandre.lureau@redhat.com>

Message-id: <20210108074101.290008-4-marcandre.lureau@redhat.com>

Patchwork-id: 100522

O-Subject: [RHEL-8.3.0.z qemu-kvm PATCH 03/10] error: Improve error.h's big comment

Bugzilla: 1913818

RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>

RH-Acked-by: Philippe Mathieu-Daudé <philmd@redhat.com>

RH-Acked-by: Stefano Garzarella <sgarzare@redhat.com>

From: Marc-André Lureau <marcandre.lureau@redhat.com>

From: Markus Armbruster <armbru@redhat.com>

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>

Message-Id: <20200707160613.848843-3-armbru@redhat.com>

Reviewed-by: Eric Blake <eblake@redhat.com>

Reviewed-by: Greg Kurz <groug@kaod.org>

(cherry picked from commit 9aac7d486cc792191c25c30851f501624b0c2751)

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>

Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>

---

 include/qapi/error.h | 51 +++++++++++++++++++++++++++++++-------------

 1 file changed, 36 insertions(+), 15 deletions(-)

diff --git a/include/qapi/error.h b/include/qapi/error.h

index 83c38f9a188..3351fe76368 100644

--- a/include/qapi/error.h

+++ b/include/qapi/error.h

@@ -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!

-- 

2.27.0