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

[Zhijian Li (Fujitsu)]

On 26/09/2023 19:52, Markus Armbruster wrote:
> "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.

Yes, i have no doubt about this.


> 
> 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?

Yes, I'd like downgrade error to a warning.


Thanks
Zhijian

> 
>>> 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);
>