netdev - Re: [PATCH v3 1/9] ptp: Add generic ptp v2 header parsing function

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Message-ID: <8f1945a4-33a2-5576-2948-aee5141f83f6@ti.com>
Date:   Wed, 5 Aug 2020 01:04:31 +0300
From:   Grygorii Strashko <grygorii.strashko@...com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
CC:     Kurt Kanzenbach <kurt@...utronix.de>,
        Petr Machata <petrm@...lanox.com>,
        Richard Cochran <richardcochran@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jiri Pirko <jiri@...lanox.com>,
        Ido Schimmel <idosch@...lanox.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>,
        Samuel Zou <zou_wei@...wei.com>, <netdev@...r.kernel.org>
Subject: Re: [PATCH v3 1/9] ptp: Add generic ptp v2 header parsing function



On 05/08/2020 00:44, Russell King - ARM Linux admin wrote:
> On Wed, Aug 05, 2020 at 12:34:47AM +0300, Grygorii Strashko wrote:
>> On 05/08/2020 00:07, Russell King - ARM Linux admin wrote:
>>> On Tue, Aug 04, 2020 at 11:56:12PM +0300, Grygorii Strashko wrote:
>>>>
>>>>
>>>> On 31/07/2020 13:06, Kurt Kanzenbach wrote:
>>>>> On Thu Jul 30 2020, Petr Machata wrote:
>>>>>> Kurt Kanzenbach <kurt@...utronix.de> writes:
>>>>>>
>>>>>>> @@ -107,6 +107,37 @@ unsigned int ptp_classify_raw(const struct sk_buff *skb)
>>>>>>>     }
>>>>>>>     EXPORT_SYMBOL_GPL(ptp_classify_raw);
>>>>>>> +struct ptp_header *ptp_parse_header(struct sk_buff *skb, unsigned int type)
>>>>>>> +{
>>>>>>> +	u8 *data = skb_mac_header(skb);
>>>>>>> +	u8 *ptr = data;
>>>>>>
>>>>>> One of the "data" and "ptr" variables is superfluous.
>>>>>
>>>>> Yeah. Can be shortened to u8 *ptr = skb_mac_header(skb);
>>>>
>>>> Actually usage of skb_mac_header(skb) breaks CPTS RX time-stamping on
>>>> am571x platform PATCH 6.
>>>>
>>>> The CPSW RX timestamp requested after full packet put in SKB, but
>>>> before calling eth_type_trans().
>>>>
>>>> So, skb->data pints on Eth header, but skb_mac_header() return garbage.
>>>>
>>>> Below diff fixes it for me.
>>>
>>> However, that's likely to break everyone else.
>>>
>>> For example, anyone calling this from the mii_timestamper rxtstamp()
>>> method, the skb will have been classified with the MAC header pushed
>>> and restored, so skb->data points at the network header.
>>>
>>> Your change means that ptp_parse_header() expects the MAC header to
>>> also be pushed.
>>>
>>> Is it possible to adjust CPTS?
>>>
>>> Looking at:
>>> drivers/net/ethernet/ti/cpsw.c... yes.
>>> drivers/net/ethernet/ti/cpsw_new.c... yes.
>>> drivers/net/ethernet/ti/netcp_core.c... unclear.
>>>
>>> If not, maybe cpts should remain unconverted - I don't see any reason
>>> to provide a generic function for one user.
>>>
>>
>> Could it be an option to pass "u8 *ptr" instead of "const struct sk_buff *skb" as
>> input parameter to ptp_parse_header()?
> 
> It needs to read from the buffer, and in order to do that, it needs to
> validate that the buffer contains sufficient data.  So, at minimum it
> needs to be a pointer and size of valid data.
> 
> I was thinking about suggesting that as a core function, with a wrapper
> for the existing interface.
> 

Then length can be added.
Otherwise not only CPTS can't benefit from this new API, but also
drivers like oki-semi/pch_gbe/pch_gbe_main.c -> pch_ptp_match()

or have to two have two APIs (name?).

ptp_parse_header1(struct sk_buff *skb, unsigned int type)
{
	u8 *data = skb_mac_header(skb);

ptp_parse_header2(struct sk_buff *skb, unsigned int type)
{
	u8 *data = skb->data;

everything else is the same.

-- 
Best regards,
grygorii