Re: [Qemu-devel] [PATCH] util/error: do not free error on error_abort

[Markus Armbruster]

Vladimir Sementsov-Ogievskiy <address@hidden> writes:

> 15.04.2019 16:08, Markus Armbruster wrote:
>> Vladimir Sementsov-Ogievskiy <address@hidden> writes:
>> 
>>> 15.04.2019 8:51, Markus Armbruster wrote:
>>>> Vladimir Sementsov-Ogievskiy <address@hidden> writes:
>>>>
>>>>> It would be nice to have Error object not freed away when debugging a
>>>>> coredump.
>>>>>
>>>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
>>>>> ---
>>>>>    util/error.c | 8 +++++---
>>>>>    1 file changed, 5 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/util/error.c b/util/error.c
>>>>> index 934a78e1b1..f9180c0f30 100644
>>>>> --- a/util/error.c
>>>>> +++ b/util/error.c
>>>>> @@ -32,9 +32,11 @@ Error *error_fatal;
>>>>>    static void error_handle_fatal(Error **errp, Error *err)
>>>>>    {
>>>>>        if (errp == &error_abort) {
>>>>> -        fprintf(stderr, "Unexpected error in %s() at %s:%d:\n",
>>>>> -                err->func, err->src, err->line);
>>>>> -        error_report_err(err);
>>>>> +        error_report("Unexpected error in %s() at %s:%d: %s",
>>>>> +                     err->func, err->src, err->line, 
>>>>> error_get_pretty(err));
>>>>> +        if (err->hint) {
>>>>> +            error_printf_unless_qmp("%s", err->hint->str);
>>>>> +        }
>>>>>            abort();
>>>>>        }
>>>>>        if (errp == &error_fatal) {
>>>>
>>>> No objections to not freeing the error object on the path to abort().
>>>>
>>>> You also format the error message differently.  Commit 1e9b65bb1ba's
>>>> example
>>>>
>>>>           Unexpected error in parse_block_error_action() at 
>>>> .../qemu/blockdev.c:322:
>>>>           qemu-system-x86_64: -drive if=none,werror=foo: 'foo' invalid 
>>>> write error action
>>>>           Aborted (core dumped)
>>>>
>>>> changes to (guesswork, not tested):
>>>>
>>>>           qemu-system-x86_64: -drive if=none,werror=foo: Unexpected error 
>>>> in parse_block_error_action() at .../qemu/blockdev.c:322: 'foo' invalid 
>>>> write error action
>>>>           Aborted (core dumped)
>>>
>>> hm. checkpatch don't allow to put \n into error_report. So, should I call 
>>> error_report twice?
>>>
>>> Transition from fprintf to error_report is OK for you?
>> 
>> Let's simply not mess with the formatting at all.  Something like:
>> 
>> (1) Inline error_report_err(), delete the error_free()
>> 
>> (2) Optional: replace fprintf() by error_printf()
>> 
>> (3) Optional: clean up the additional copy of
>> 
>>          if (err->hint) {
>>              error_printf_unless_qmp("%s", err->hint->str);
>>          }
>> 
>> (3a) Either create a helper function, replacing all three copies,
>> 
>> (3b) Or simply delete the new copy from the path leading to abort(),
>>       since the hint is unlikely to be useful there.
>> 
>
> Why we print error always but hint only "unless_qmp"?

"Hints" are intended for giving hints to a human user (although they are
misused for other purposes in places):

/*
 * Append a printf-style human-readable explanation to an existing error.
 * If the error is later reported to a human user with
 * error_report_err() or warn_report_err(), the hints will be shown,
 * too.  If it's reported via QMP, the hints will be ignored.
 * Intended use is adding helpful hints on the human user interface,
 * e.g. a list of valid values.  It's not for clarifying a confusing
 * error message.
 * @errp may be NULL, but not &error_fatal or &error_abort.
 * Trivially the case if you call it only after error_setg() or
 * error_propagate().
 * May be called multiple times.  The resulting hint should end with a
 * newline.
 */
void error_append_hint(Error **errp, const char *fmt, ...)
    GCC_FMT_ATTR(2, 3);