netdev - Re: [PATCH net-next 5/7] s390/qeth: improve endianness handling

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Message-Id: <8056aa76-8e2d-805e-1037-927714e9bfab@linux.vnet.ibm.com>
Date:   Fri, 7 Apr 2017 14:33:21 +0200
From:   Ursula Braun <ubraun@...ux.vnet.ibm.com>
To:     David Laight <David.Laight@...LAB.COM>,
        "davem@...emloft.net" <davem@...emloft.net>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "jwi@...ux.vnet.ibm.com" <jwi@...ux.vnet.ibm.com>,
        "schwidefsky@...ibm.com" <schwidefsky@...ibm.com>,
        "heiko.carstens@...ibm.com" <heiko.carstens@...ibm.com>,
        "raspl@...ux.vnet.ibm.com" <raspl@...ux.vnet.ibm.com>,
        Hans Wippel <hwippel@...ux.vnet.ibm.com>,
        Julian Wiedmann <jwi@...ux.vnet.ibm.com>
Subject: Re: [PATCH net-next 5/7] s390/qeth: improve endianness handling



On 04/07/2017 01:25 PM, David Laight wrote:
> From: Ursula Braun
>> Sent: 05 April 2017 09:40
>> From: Hans Wippel <hwippel@...ux.vnet.ibm.com>
>>
>> Avoid endianness warnings reported by sparse by (1) using endianness
>> conversions for assigning and using network packet fields, and (2)
>> removing unnecessary endianness conversions from qeth_l3_rebuild_skb. No
>> functional changes.
>>
>> Signed-off-by: Hans Wippel <hwippel@...ux.vnet.ibm.com>
>> Signed-off-by: Ursula Braun <ubraun@...ux.vnet.ibm.com>
>> ---
>>  drivers/s390/net/qeth_core.h      |  4 ++--
>>  drivers/s390/net/qeth_core_main.c | 11 +++++-----
>>  drivers/s390/net/qeth_l3_main.c   | 46 +++++++++++++++++++--------------------
>>  drivers/s390/net/qeth_l3_sys.c    |  4 ++--
>>  4 files changed, 33 insertions(+), 32 deletions(-)
>>
>> diff --git a/drivers/s390/net/qeth_core.h b/drivers/s390/net/qeth_core.h
>> index 22aa2cd..6764ab9 100644
>> --- a/drivers/s390/net/qeth_core.h
>> +++ b/drivers/s390/net/qeth_core.h
>> @@ -844,9 +844,9 @@ static inline int qeth_get_ip_version(struct sk_buff *skb)
>>  {
>>  	__be16 *p = &((struct ethhdr *)skb->data)->h_proto;
>>
>> -	if (*p == ETH_P_8021Q)
>> +	if (be16_to_cpu(*p) == ETH_P_8021Q)
>>  		p += 2;
>> -	switch (*p) {
>> +	switch (be16_to_cpu(*p)) {
>>  	case ETH_P_IPV6:
> 
> These are definitely 'functional changes' on LE systems.
s390 is Big Endian; thus the change is basicly a NOP. 
The only purpose of this kind of patches is getting rid
of sparse warnings with our code.
> 
> Also it is generally better to byteswap the constants.
> 
> 	David
>