Re: [Qemu-devel] [PATCH 2/2] s390x/3270: handle writes of arbitrary length

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

On 09/21/2017 11:23 AM, Cornelia Huck wrote:
> On Wed, 20 Sep 2017 19:23:14 +0200
> Halil Pasic <pasic@linux.vnet.ibm.com> wrote:
> 
>> The problem is, that the current implementation places unrealistic and
>> arbitrary constraints on the length of writes to the device (that is the
>> outbound requests), by asserting ccw.count being such that that even the
>> worst case escaped payload will fit an  more or less arbitrary sized
>> buffer. Actually on protocol level there is nothing to justify such
>> a limitation.
>>
>> Another strange thing is the return value which more or less reflects
>> the size (written) after escaping instead of before escaping. This
>> is strange, because this return value is used to calculate SCSW.count.
> 
> Didn't the Linux driver care about the count?
> 

Maybe Jason can answer that. I did only most basic testing with my patch
applied (and basically no testing without my changes).

>From code perspective I'm sure it does for the reads. For the writes
I did not look into that.

Halil

>>
>> Let us teach 3270 how to deal with arbitrary long writes.
>>
>> Signed-off-by: Halil Pasic <pasic@linux.vnet.ibm.com>
>> Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
>> Reviewed-by: Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
>> Reported-by: Jason J . Herne <jjherne@linux.vnet.ibm.com>
>> Tested-by: Jason J . Herne <jjherne@linux.vnet.ibm.com>
>> ---
>>  hw/char/terminal3270.c | 30 ++++++++++++++++++------------
>>  1 file changed, 18 insertions(+), 12 deletions(-)
> 
> Looks good.
>