Re: [Qemu-devel] [PATCH arm-devs v1 10/13] net/cadence_gem: Fix small packet FCS stripping

[Peter Crosthwaite]

On Mon, Dec 2, 2013 at 10:26 PM, Peter Maydell <address@hidden> wrote:
> On 2 December 2013 07:14, Peter Crosthwaite
> <address@hidden> wrote:
>> The minimum packet size is 64, however this is before FCS stripping
>> occurs. So when FCS stripping the minimum packet size is 60. Fix.
>>
>> Reported-by: Deepika Dhamija <address@hidden>
>> Signed-off-by: Peter Crosthwaite <address@hidden>
>> ---
>>
>>  hw/net/cadence_gem.c | 13 ++++++++-----
>>  1 file changed, 8 insertions(+), 5 deletions(-)
>>
>> diff --git a/hw/net/cadence_gem.c b/hw/net/cadence_gem.c
>> index eb0fa95..babd39d 100644
>> --- a/hw/net/cadence_gem.c
>> +++ b/hw/net/cadence_gem.c
>> @@ -674,6 +674,14 @@ static ssize_t gem_receive(NetClientState *nc, const 
>> uint8_t *buf, size_t size)
>>      rxbuf_offset = (s->regs[GEM_NWCFG] & GEM_NWCFG_BUFF_OFST_M) >>
>>                     GEM_NWCFG_BUFF_OFST_S;
>>
>> +    /* Pad to minimum length. Assume FCS field is stripped, logic
>> +     * below will increment it to the real minimum of 64 when
>> +     * not FCS stripping
>> +     */
>> +    if (size < 60) {
>> +        size = 60;
>> +    }
>> +
>>      /* The configure size of each receive buffer.  Determines how many
>>       * buffers needed to hold this packet.
>>       */
>> @@ -707,11 +715,6 @@ static ssize_t gem_receive(NetClientState *nc, const 
>> uint8_t *buf, size_t size)
>>          size += 4;
>>      }
>>
>> -    /* Pad to minimum length */
>> -    if (size < 64) {
>> -        size = 64;
>> -    }
>> -
>
> This change moves the padding of size from below the point where
> we initialize bytes_to_copy to above it, so now bytes_to_copy will
> get the padded value rather than the unpadded value. If this is deliberate
> it should probably be spelled out somewhere. (See also comments on
> earlier patch.)
>

So I cant see a good reason for that change. Reverted - just moved the
added hunk to below the bytes_to_copy =. Stress tests and linux tests
still pass.

Regards,
Peter

> thanks
> -- PMM
>