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[PULL 02/53] error: Improve error.h's big comment
From: |
Markus Armbruster |
Subject: |
[PULL 02/53] error: Improve error.h's big comment |
Date: |
Tue, 7 Jul 2020 23:24:12 +0200 |
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>
---
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 e8960eaad5..6d079c58b7 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!
--
2.26.2
- [PULL 00/53] Error reporting patches patches for 2020-07-07, Markus Armbruster, 2020/07/08
- [PULL 50/53] fw_cfg: Use ERRP_GUARD(), Markus Armbruster, 2020/07/08
- [PULL 02/53] error: Improve error.h's big comment,
Markus Armbruster <=
- [PULL 38/53] block/parallels: Simplify parallels_open() after previous commit, Markus Armbruster, 2020/07/08
- [PULL 08/53] qemu-option: Make uses of find_desc_by_name() more similar, Markus Armbruster, 2020/07/08
- [PULL 04/53] qdev: Use returned bool to check for qdev_realize() etc. failure, Markus Armbruster, 2020/07/08
- [PULL 07/53] qemu-option: Check return value instead of @err where convenient, Markus Armbruster, 2020/07/08
- [PULL 32/53] qdev: Use returned bool to check for failure, Coccinelle part, Markus Armbruster, 2020/07/08
- [PULL 06/53] virtio-crypto-pci: Tidy up virtio_crypto_pci_realize(), Markus Armbruster, 2020/07/08
- [PULL 44/53] qdev: Ignore Error objects where the return value suffices, Markus Armbruster, 2020/07/08
- [PULL 52/53] nbd: Use ERRP_GUARD(), Markus Armbruster, 2020/07/08
- [PULL 27/53] qom: Make functions taking Error ** return bool, not void, Markus Armbruster, 2020/07/08
- [PULL 09/53] qemu-option: Factor out helper find_default_by_name(), Markus Armbruster, 2020/07/08