[dpdk-dev] [PATCH] ethdev: extend flow metadata

[Yongseok Koh]

> On Jul 10, 2019, at 5:26 AM, Thomas Monjalon <thomas at monjalon.net> wrote:
> 
> 10/07/2019 14:01, Bruce Richardson:
>> On Wed, Jul 10, 2019 at 12:07:43PM +0200, Olivier Matz wrote:
>>> On Wed, Jul 10, 2019 at 10:55:34AM +0100, Bruce Richardson wrote:
>>>> On Wed, Jul 10, 2019 at 11:31:56AM +0200, Olivier Matz wrote:
>>>>> On Thu, Jul 04, 2019 at 04:21:22PM -0700, Yongseok Koh wrote:
>>>>>> Currently, metadata can be set on egress path via mbuf tx_meatadata field
>>>>>> with PKT_TX_METADATA flag and RTE_FLOW_ITEM_TYPE_RX_META matches metadata.
>>>>>> 
>>>>>> This patch extends the usability.
>>>>>> 
>>>>>> 1) RTE_FLOW_ACTION_TYPE_SET_META
>>>>>> 
>>>>>> When supporting multiple tables, Tx metadata can also be set by a rule and
>>>>>> matched by another rule. This new action allows metadata to be set as a
>>>>>> result of flow match.
>>>>>> 
>>>>>> 2) Metadata on ingress
>>>>>> 
>>>>>> There's also need to support metadata on packet Rx. Metadata can be set by
>>>>>> SET_META action and matched by META item like Tx. The final value set by
>>>>>> the action will be delivered to application via mbuf metadata field with
>>>>>> PKT_RX_METADATA ol_flag.
>>>>>> 
>>>>>> For this purpose, mbuf->tx_metadata is moved as a separate new field and
>>>>>> renamed to 'metadata' to support both Rx and Tx metadata.
>>>>>> 
>>>>>> For loopback/hairpin packet, metadata set on Rx/Tx may or may not be
>>>>>> propagated to the other path depending on HW capability.
>>>>>> 
>>>>>> Signed-off-by: Yongseok Koh <yskoh at mellanox.com>
>>>>> 
>>>>>> --- a/lib/librte_mbuf/rte_mbuf.h
>>>>>> +++ b/lib/librte_mbuf/rte_mbuf.h
>>>>>> @@ -648,17 +653,6 @@ struct rte_mbuf {
>>>>>> 			/**< User defined tags. See rte_distributor_process() */
>>>>>> 			uint32_t usr;
>>>>>> 		} hash;                   /**< hash information */
>>>>>> -		struct {
>>>>>> -			/**
>>>>>> -			 * Application specific metadata value
>>>>>> -			 * for egress flow rule match.
>>>>>> -			 * Valid if PKT_TX_METADATA is set.
>>>>>> -			 * Located here to allow conjunct use
>>>>>> -			 * with hash.sched.hi.
>>>>>> -			 */
>>>>>> -			uint32_t tx_metadata;
>>>>>> -			uint32_t reserved;
>>>>>> -		};
>>>>>> 	};
>>>>>> 
>>>>>> 	/** Outer VLAN TCI (CPU order), valid if PKT_RX_QINQ is set. */
>>>>>> @@ -727,6 +721,11 @@ struct rte_mbuf {
>>>>>> 	 */
>>>>>> 	struct rte_mbuf_ext_shared_info *shinfo;
>>>>>> 
>>>>>> +	/** Application specific metadata value for flow rule match.
>>>>>> +	 * Valid if PKT_RX_METADATA or PKT_TX_METADATA is set.
>>>>>> +	 */
>>>>>> +	uint32_t metadata;
>>>>>> +
>>>>>> } __rte_cache_aligned;
>>>>> 
>>>>> This will break the ABI, so we cannot put it in 19.08, and we need a
>>>>> deprecation notice.
>>>>> 
>>>> Does it actually break the ABI? Adding a new field to the mbuf should only
>>>> break the ABI if it either causes new fields to move or changes the
>>>> structure size. Since this is at the end, it's not going to move any older
>>>> fields, and since everything is cache-aligned I don't think the structure
>>>> size changes either.
>>> 
>>> I think it does break the ABI: in previous version, when the PKT_TX_METADATA
>>> flag is set, the associated value is put in m->tx_metadata (offset 44 on
>>> x86-64), and in the next version, it will be in m->metadata (offset 112). So,
>>> these 2 versions are not binary compatible.
>>> 
>>> Anyway, at least it breaks the API.
>> 
>> Ok, I misunderstood. I thought it was the structure change itself you were
>> saying broke the ABI. Yes, putting the data in a different place is indeed
>> an ABI break.
> 
> We could add the new field and keep the old one unused,
> so it does not break the ABI.

Still breaks ABI if PKT_TX_METADATA is set. :-) In order not to break it, I can
keep the current union'd field (tx_metadata) as is with PKT_TX_METADATA, add
the new one at the end and make it used with the new PKT_RX_METADATA.

> However I suppose everybody will prefer a version using dynamic fields.
> Is someone against using dynamic field for such usage?

However, given that the amazing dynamic fields is coming soon (thanks for your
effort, Olivier and Thomas!), I'd be honored to be the first user of it.

Olivier, I'll take a look at your RFC.


Thanks,
Yongseok