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error: Fix use of error_prepend() with &error_fatal, &error_abort

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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>
This commit is contained in:
Markus Armbruster 2018-10-17 10:26:25 +02:00
parent d7ecf71238
commit 4b5766488f
13 changed files with 61 additions and 33 deletions
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14
include/qapi/error.h
View file

@ -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_setg_win32_internal(Error **errp,
*/
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().