Re: [PATCH 50/52] migration/rdma: Silence qemu_rdma_cleanup()

[Markus Armbruster]

"Zhijian Li (Fujitsu)" <lizhijian@fujitsu.com> writes:

> On 18/09/2023 22:42, Markus Armbruster wrote:
>> Functions that use an Error **errp parameter to return errors should
>> not also report them to the user, because reporting is the caller's
>> job.  When the caller does, the error is reported twice.  When it
>> doesn't (because it recovered from the error), there is no error to
>> report, i.e. the report is bogus.
>> 
>> qemu_rdma_source_init(), qemu_rdma_connect(),
>> rdma_start_incoming_migration(), and rdma_start_outgoing_migration()
>> violate this principle: they call error_report() via
>> qemu_rdma_cleanup().
>> 
>> Moreover, qemu_rdma_cleanup() can't fail.  It is called on error
>> paths, and QIOChannel close and finalization.  Are the conditions it
>> reports really errors?  I doubt it.
>
> I'm not very sure, it's fine if it's call from the error path. but when
> the caller is migration_cancle from HMP/QMP, shall we report something more
> though we know QEMU can recover.
>
> maybe change to warning etc...

The part I'm sure about is that reporting an error to the user is wrong
when we actually recover from the error.  Which qemu_rdma_cleanup()
does.

I'm not sure whether the (complicated!) condition that triggers
qemu_rdma_cleanup()'s ill-advised error report needs to be reported in
some other form.  The remainder of the function ignores failure...

If you think we should to downgrade the error to a warning, and no
maintainer disagrees, then I'll downgrade.  Do you?

>> Clean this up: silence qemu_rdma_cleanup().  I believe that's fine for
>> all these callers.  If it isn't, we need to convert to Error instead.
>> 
>> Signed-off-by: Markus Armbruster <armbru@redhat.com>
>> ---
>>   migration/rdma.c | 6 +-----
>>   1 file changed, 1 insertion(+), 5 deletions(-)
>> 
>> diff --git a/migration/rdma.c b/migration/rdma.c
>> index d9f80ef390..be2db7946d 100644
>> --- a/migration/rdma.c
>> +++ b/migration/rdma.c
>> @@ -2330,7 +2330,6 @@ static int qemu_rdma_write(QEMUFile *f, RDMAContext 
>> *rdma,
>>   
>>   static void qemu_rdma_cleanup(RDMAContext *rdma)
>>   {
>> -    Error *err = NULL;
>>       int idx;
>>   
>>       if (rdma->cm_id && rdma->connected) {
>> @@ -2341,10 +2340,7 @@ static void qemu_rdma_cleanup(RDMAContext *rdma)
>>                                          .type = RDMA_CONTROL_ERROR,
>>                                          .repeat = 1,
>>                                        };
>> -            error_report("Early error. Sending error.");
>> -            if (qemu_rdma_post_send_control(rdma, NULL, &head, &err) < 0) {
>> -                error_report_err(err);
>> -            }
>> +            qemu_rdma_post_send_control(rdma, NULL, &head, NULL);
>>           }
>>   
>>           rdma_disconnect(rdma->cm_id);