Re: [RFC v1 1/4] vfio-ccw: Set orb.cmd.c64 before calling ccwchain_handle_ccw

[Eric Farman <farman@linux.ibm.com>]

On 7/2/19 9:56 AM, Farhan Ali wrote:
> 
> 
> On 07/02/2019 04:26 AM, Cornelia Huck wrote:
>> On Mon,  1 Jul 2019 12:23:43 -0400
>> Farhan Ali <alifm@linux.ibm.com> wrote:
>>
>>> Because ccwchain_handle_ccw calls ccwchain_calc_length and
>>> as per the comment we should set orb.cmd.c64 before calling
>>> ccwchanin_calc_length.
>>>
>>> Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
>>> ---
>>>   drivers/s390/cio/vfio_ccw_cp.c | 10 +++++-----
>>>   1 file changed, 5 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/s390/cio/vfio_ccw_cp.c
>>> b/drivers/s390/cio/vfio_ccw_cp.c
>>> index d6a8dff..5ac4c1e 100644
>>> --- a/drivers/s390/cio/vfio_ccw_cp.c
>>> +++ b/drivers/s390/cio/vfio_ccw_cp.c
>>> @@ -640,16 +640,16 @@ int cp_init(struct channel_program *cp, struct
>>> device *mdev, union orb *orb)
>>>       memcpy(&cp->orb, orb, sizeof(*orb));
>>>       cp->mdev = mdev;
>>>   -    /* Build a ccwchain for the first CCW segment */
>>> -    ret = ccwchain_handle_ccw(orb->cmd.cpa, cp);
>>> -    if (ret)
>>> -        cp_free(cp);
>>> -
>>>       /* It is safe to force: if not set but idals used
>>>        * ccwchain_calc_length returns an error.
>>>        */
>>>       cp->orb.cmd.c64 = 1;
>>>   +    /* Build a ccwchain for the first CCW segment */
>>> +    ret = ccwchain_handle_ccw(orb->cmd.cpa, cp);
>>> +    if (ret)
>>> +        cp_free(cp);
>>> +
>>>       if (!ret)
>>>           cp->initialized = true;
>>>   
>>
>> Hm... has this ever been correct, or did this break only with the
>> recent refactorings?
>>
>> (IOW, what should Fixes: point to?)

Yeah, that looks like it should blame my refactoring.

>>
>>
> 
> I think it was correct before some of the new refactoring we did. But we
> do need to set before calling ccwchain_calc_length, because the function
> does have a check for orb.cmd.64. I will see which exact commit did it.

I get why that check exists, but does anyone know why it's buried in
ccwchain_calc_length()?  Is it simply because ccwchain_calc_length()
assumes to be working on Format-1 CCWs?  I don't think that routine
cares if it's an IDA or not, an it'd be nice if we could put a check for
the supported IDA formats somewhere up front.

> 
> Thanks
> Farhan