> -----Original Message----- > From: Olivier Matz [mailto:olivier.m...@6wind.com] > Sent: Thursday, July 11, 2019 16:21 > To: Wang, Haiyue <haiyue.w...@intel.com> > Cc: dev@dpdk.org > Subject: Re: [dpdk-dev] [RFC] mbuf: support dynamic fields and flags > > On Thu, Jul 11, 2019 at 08:04:00AM +0000, Wang, Haiyue wrote: > > > -----Original Message----- > > > From: Olivier Matz [mailto:olivier.m...@6wind.com] > > > Sent: Thursday, July 11, 2019 15:26 > > > To: Wang, Haiyue <haiyue.w...@intel.com> > > > Cc: dev@dpdk.org > > > Subject: Re: [dpdk-dev] [RFC] mbuf: support dynamic fields and flags > > > > > > Hi, > > > > > > On Wed, Jul 10, 2019 at 05:14:33PM +0000, Wang, Haiyue wrote: > > > > Hi, > > > > > > > > Sounds cool, just have some questions inline. > > > > > > > > > -----Original Message----- > > > > > From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Olivier Matz > > > > > Sent: Wednesday, July 10, 2019 17:29 > > > > > To: dev@dpdk.org > > > > > Subject: [dpdk-dev] [RFC] mbuf: support dynamic fields and flags > > > > > > > > > > Many features require to store data inside the mbuf. As the room in > > > > > mbuf > > > > > structure is limited, it is not possible to have a field for each > > > > > feature. Also, changing fields in the mbuf structure can break the API > > > > > or ABI. > > > > > > > > > > This commit addresses these issues, by enabling the dynamic > > > > > registration > > > > > of fields or flags: > > > > > > > > > > - a dynamic field is a named area in the rte_mbuf structure, with a > > > > > given size (>= 1 byte) and alignment constraint. > > > > > - a dynamic flag is a named bit in the rte_mbuf structure. > > > > > > > > > > The typical use case is a PMD that registers space for an offload > > > > > feature, when the application requests to enable this feature. As > > > > > the space in mbuf is limited, the space should only be reserved if it > > > > > is going to be used (i.e when the application explicitly asks for it). > > > > > > > > > > The registration can be done at any moment, but it is not possible > > > > > to unregister fields or flags for now. > > > > > > > > > > Signed-off-by: Olivier Matz <olivier.m...@6wind.com> > > > > > > (...) > > > > > > > > +/** > > > > > + * @file > > > > > + * RTE Mbuf dynamic fields and flags > > > > > + * > > > > > + * Many features require to store data inside the mbuf. As the room > > > > > in > > > > > + * mbuf structure is limited, it is not possible to have a field for > > > > > + * each feature. Also, changing fields in the mbuf structure can > > > > > break > > > > > + * the API or ABI. > > > > > + * > > > > > + * This module addresses this issue, by enabling the dynamic > > > > > + * registration of fields or flags: > > > > > + * > > > > > + * - a dynamic field is a named area in the rte_mbuf structure, with > > > > > a > > > > > + * given size (>= 1 byte) and alignment constraint. > > > > > + * - a dynamic flag is a named bit in the rte_mbuf structure. > > > > > + * > > > > > + * The typical use case is a PMD that registers space for an offload > > > > > + * feature, when the application requests to enable this feature. As > > > > > + * the space in mbuf is limited, the space should only be reserved > > > > > if it > > > > > + * is going to be used (i.e when the application explicitly asks for > > > > > it). > > > > > + * > > > > > + * The registration can be done at any moment, but it is not possible > > > > > + * to unregister fields or flags for now. > > > > > + * > > > > > + * Example of use: > > > > > + * > > > > > + * - RTE_MBUF_DYN_<feature>_(ID|SIZE|ALIGN) are defined in this file > > > > > > > > Does it means that all PMDs define their own > > > > 'RTE_MBUF_DYN_<feature>_(ID|SIZE|ALIGN)' > > > > here ? In other words, each PMD can expose its private DYN_<feature> > > > > here for public > > > > using ? > > > > > > For generic fields, I think they should be declared in this file. For > > > instance, if we decide to replace the current m->timestamp field by a > > > dynamic field, we should add like this: > > > > > > #define RTE_MBUF_DYN_TIMESTAMP_ID "rte_timestamp" > > > #define RTE_MBUF_DYN_TIMESTAMP_SIZE sizeof(uint64_t) > > > #define RTE_MBUF_DYN_TIMESTAMP_ALIGN __alignof__(uint64_t) > > > > > > If the feature is PMD-specific, the defines could be exposed in a > > > PMD header. > > > > > > > Now, understand the comments a little : ... must not define identifers > > prefixed with "rte_", > > which are reserved for standard features. Seems have big plan ? > > The dynamic field can also be used by an external application or by an > external library. For instance, a field to tag a packet, like skb->mark > in linux. In this case, id, size and alignment would be defined outside > dpdk subtree. > > To avoid name conflicts, I think we should define a convention for > identifiers, so they are in different namespaces: > > - "rte_*" for identifiers declared inside dpdk subtree > - any other name for identifiers declared in an external application or > library
Very clearer now, thanks, this convention can be in programming guide document. :)
