Re: [Qemu-devel] [PATCH 1/9] s390x/css: fix cc handling for XSCH

[Halil Pasic <pasic@linux.vnet.ibm.com>]

On 08/31/2017 10:42 AM, Cornelia Huck wrote:
> On Thu, 31 Aug 2017 09:32:49 +0200
> Thomas Huth <thuth@redhat.com> wrote:
> 
>> On 31.08.2017 08:38, Cornelia Huck wrote:
>>> On Thu, 31 Aug 2017 07:51:17 +0200
>>> Thomas Huth <thuth@redhat.com> wrote:
>>>   
>>>> On 30.08.2017 18:36, Halil Pasic wrote:  
>>>>> The function ioinst_handle_xsch is presenting cc 2 when it's supposed to
>>>>> present cc 1 and the other way around, because css_do_xsch has the error
>>>>> codes mixed up. Fixing the error codes also fixes the priority.
>>>>>
>>>>> Let us fix this.    
>>>>
>>>> (Nit: In case you respin, I'd suggest to remove the last sentence. You
>>>> already used "fix" two times in the previous one)  
>>>
>>> I can also remove it on applying, if Halil agrees (I have not yet
>>> reviewed it, though).
>>>   
>>>>  
>>>>> Signed-off-by: Halil Pasic <pasic@linux.vnet.ibm.com>
>>>>> Reported-by: Pierre Morel<pmorel@linux.vnet.ibm.com>    
>>>>
>>>> Space missing -------------^  
>>>
>>> And I can also add that space on applying :)
>>>   
>>>>  
>>>>> ---
>>>>>  hw/s390x/css.c | 4 ++--
>>>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/hw/s390x/css.c b/hw/s390x/css.c
>>>>> index 1880b1a0ff..a50fb0727e 100644
>>>>> --- a/hw/s390x/css.c
>>>>> +++ b/hw/s390x/css.c
>>>>> @@ -1281,12 +1281,12 @@ int css_do_xsch(SubchDev *sch)
>>>>>          (!(s->ctrl &
>>>>>             (SCSW_ACTL_RESUME_PEND | SCSW_ACTL_START_PEND | SCSW_ACTL_SUSP))) ||
>>>>>          (s->ctrl & SCSW_ACTL_SUBCH_ACTIVE)) {
>>>>> -        ret = -EINPROGRESS;
>>>>> +        ret = -EBUSY;
>>>>>          goto out;
>>>>>      }
>>>>>  
>>>>>      if (s->ctrl & SCSW_CTRL_MASK_STCTL) {
>>>>> -        ret = -EBUSY;
>>>>> +        ret = -EINPROGRESS;
>>>>>          goto out;
>>>>>      }    
>>>>
>>>> Using both, EBUSY and EINPROGRESS as error codes sounds very confusing
>>>> to me here ... what's the difference between busy and in-progress? So
>>>> while you're at it, maybe you could replace the code for CC 2 ("CANCEL
>>>> SUBCHANNEL not applicable") with a different error code?  
>>>
>>> IIRC, I used these two as they matched my idea of what happens best
>>> (there's a difference between "subchannel is busy" and "the I/O is
>>> already in progress, too late to cancel"). "xsch not applicable" is
>>> very hard to translate to an Unix error code :/  
>>
>> OK, the codes make more sense with your description ==> Maybe simply add
>> a proper comment for each of the return codes?
> 
> Taking a step back and looking at the other I/O instructions and their
> implementation in qemu:
> 
> - For those instructions that can set it, cc 1 is set when the
>   subchannel is status pending. That's usually the "default" branch in
>   ioinst.c.
> - cc 2 is set when the subchannel is "busy" (or, in the case of xsch,
>   "not applicable for xsch"... sigh) This is supposed to be handled via
>   -EBUSY.
> 
> So, there are actually two problems with the current implementation of
> xsch:
> 
> - The return codes are switched around, which this patch fixes.
> - But "status pending" should also take precedence over "not
>   applicable", if I read the PoP correctly, so the second if needs to
>   be moved up.

You are right and I was wrong. "Condition code 1 has precedence over
condition code 2." So it's 3 > 1 > 2 (and I remembered 3 > 2 > 1).

I will fix this for v2.

> 
> And yes, it makes sense do add some comments...
> 

If we apply the series as a whole adding comments would an overkill
IMHO. We will switch this to iret.cc = ? so it should become obvious.