Re: [dpdk-dev] [PATCH] net: fix Tx VLAN flag for offload emulation

[Chas Williams <3chas3@gmail.com>]

On 3/26/19 12:50 PM, Ferruh Yigit wrote:
> On 3/25/2019 3:05 PM, Chas Williams wrote:
>> From: Bill Hong <bhong@brocade.com>
>>
>> A PMD might use rte_vlan_insert to implement Tx VLAN offload.  Typically
>> the PMD will insert the VLAN header in the transmit path and then attempt
>> to send the packets. If this fails, the packets are returned to
>> the application which may attempt to send these packets again. If the
>> PKT_TX_VLAN flag is not cleared, the transmit path may attempt to insert
>> the VLAN header again.
>>
>> Fixes: 47aa48b969f8 ("net: fix stripped VLAN flag for offload emulation");
>> Cc: stable@dpdk.org
>>
>> Signed-off-by: Bill Hong <bhong@brocade.com>
>> Signed-off-by: Chas Williams <chas3@att.com>
>> ---
>>   lib/librte_net/rte_ether.h | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/lib/librte_net/rte_ether.h b/lib/librte_net/rte_ether.h
>> index c2c5e249f..e0d831113 100644
>> --- a/lib/librte_net/rte_ether.h
>> +++ b/lib/librte_net/rte_ether.h
>> @@ -408,7 +408,7 @@ static inline int rte_vlan_insert(struct rte_mbuf **m)
>>   	vh = (struct vlan_hdr *) (nh + 1);
>>   	vh->vlan_tci = rte_cpu_to_be_16((*m)->vlan_tci);
>>   
>> -	(*m)->ol_flags &= ~PKT_RX_VLAN_STRIPPED;
>> +	(*m)->ol_flags &= ~(PKT_RX_VLAN_STRIPPED | PKT_TX_VLAN);
> 
> Hi Chas,
> 
> Looks reasonable, AFAIK, PKT_TX_VLAN flag means 'mbuf->vlan_tci' has valid value
> and a request from application to driver to insert VLAN information.
> After successful insertion flag can be removed.
> 
> But in mbuf header, flags documented as:
> PKT_TX_VLAN: TX packet is a 802.1q VLAN packet.
> PKT_TX_QINQ: TX packet with double VLAN inserted.

Note the usage slightly below:

	/**
	 * Bitmask of all supported packet Tx offload features flags,
	 * which can be set for packet.
	 */
	#define PKT_TX_OFFLOAD_MASK (    \
			PKT_TX_OUTER_IPV6 |      \
			PKT_TX_OUTER_IPV4 |      \
			PKT_TX_OUTER_IP_CKSUM |  \
			PKT_TX_VLAN_PKT |        \

So this implies that PKT_TX_VLAN_PKT (which is PKT_TX_VLAN's old name)
is an offload feature, not that the actual packet has an 802.1q header
(offloaded or otherwise).

The same seems to apply for PKT_TX_QINQ.

> Hi Oliver,
> 
> Is above comments correct, or I am missing something J
> 
> 
> Also here cleaning 'PKT_RX_VLAN_STRIPPED' looks like to say 'vlan' information
> is not stripped but in the packet data, but 'RX' in this context can be
> confusing, should we have a more generic 'PKT_VLAN_STRIPPED' ?
>