[PATCH v6 4/8] ethdev: use GRE protocol struct for flow matching

[Ferruh Yigit]

On 2/2/2023 5:16 PM, Thomas Monjalon wrote:
> 02/02/2023 13:44, Ferruh Yigit:
>> --- a/lib/net/rte_gre.h
>> +++ b/lib/net/rte_gre.h
>> @@ -28,6 +28,8 @@ extern "C" {
>>   */
>>  __extension__
>>  struct rte_gre_hdr {
>> +       union {
>> +               struct {
>>  #if RTE_BYTE_ORDER == RTE_LITTLE_ENDIAN
>>         uint16_t res2:4; /**< Reserved */
>>         uint16_t s:1;    /**< Sequence Number Present bit */
>> @@ -45,6 +47,9 @@ struct rte_gre_hdr {
>>         uint16_t res3:5; /**< Reserved */
>>         uint16_t ver:3;  /**< Version Number */
>>  #endif
>> +               };
>> +               rte_be16_t c_rsvd0_ver;
>> +       };
>>         uint16_t proto;  /**< Protocol Type */
> 
> Why adding an unioned field c_rsvd0_ver?
> 
> 

Because existing usage in the drivers require to access these fields as
a single 16 bytes variable.

like mlx was using it as:
`X(SET_BE16,	gre_c_ver, v->c_rsvd0_ver, rte_flow_item_gre) \`

When all usage switched to flow item specific fields to generic headers,
there needs a way to represent this in the generic header.

By adding 'c_rsvd0_ver' to generic header it becomes:
`X(SET_BE16,	gre_c_ver, v->hdr.c_rsvd0_ver, rte_flow_item_gre) \`


Or another sample, previous version of code was updated as following:
`
 -	size = sizeof(((struct rte_flow_item_gre *)NULL)->c_rsvd0_ver);
 +	size = sizeof(((struct rte_flow_item_gre *)NULL)->hdr.proto);
`

Because generic field to represent 'c_rsvd0_ver' is missing, 'hdr.proto'
was used, this was wrong.
Although the sizes of fields are same and functionally works, they are
different fields, this is worse than sizeof(uint16_t);


Another usage in testpmd:
`
  	[ITEM_GRE_C_RSVD0_VER] = {
  		.name = "c_rsvd0_ver",
 @@ -4082,7 +4082,7 @@ static const struct token token_list[] = {
  		.next = NEXT(item_gre, NEXT_ENTRY(COMMON_UNSIGNED),
   			     item_param),
  		.args = ARGS(ARGS_ENTRY_HTON(struct rte_flow_item_gre,
 -					     c_rsvd0_ver)),
 +					     hdr.c_rsvd0_ver)),
`


But looking it again perhaps it can be named differently, because it is
not a reserved field in the generic header, though I am not sure what
can be a good variable name.