RE: [EXT] Re: [PATCH v4 2/3] ethdev: add mbuf dynfield for incomplete IP reassembly

[Akhil Goyal <gakhil@marvell.com>]

> On 2/7/2022 2:20 PM, Akhil Goyal wrote:
> >> On 2/4/2022 10:13 PM, Akhil Goyal wrote:
> >>> Hardware IP reassembly may be incomplete for multiple reasons like
> >>> reassembly timeout reached, duplicate fragments, etc.
> >>> To save application cycles to process these packets again, a new
> >>> mbuf dynflag is added to show that the mbuf received is not
> >>> reassembled properly.
> >>>
> >>> Now if this dynflag is set, application can retrieve corresponding
> >>> chain of mbufs using mbuf dynfield set by the PMD. Now, it will be
> >>> up to application to either drop those fragments or wait for more time.
> >>>
> >>> Signed-off-by: Akhil Goyal <gakhil@marvell.com>
> >>> Change-Id: I118847cd6269da7e6313ac4e0d970d790dfef1ff
> >>> ---
> >>>    lib/ethdev/ethdev_driver.h |  8 ++++++++
> >>>    lib/ethdev/rte_ethdev.c    | 28 ++++++++++++++++++++++++++++
> >>>    lib/ethdev/rte_ethdev.h    | 17 +++++++++++++++++
> >>>    lib/ethdev/version.map     |  1 +
> >>>    lib/mbuf/rte_mbuf_dyn.h    |  9 +++++++++
> >>>    5 files changed, 63 insertions(+)
> >>>
> >>> diff --git a/lib/ethdev/ethdev_driver.h b/lib/ethdev/ethdev_driver.h
> >>> index 8fe77f283f..6cfb266f7d 100644
> >>> --- a/lib/ethdev/ethdev_driver.h
> >>> +++ b/lib/ethdev/ethdev_driver.h
> >>> @@ -1707,6 +1707,14 @@ int
> >>>    rte_eth_hairpin_queue_peer_unbind(uint16_t cur_port, uint16_t
> >> cur_queue,
> >>>    				  uint32_t direction);
> >>>
> >>> +/**
> >>> + * @internal
> >>> + * Register mbuf dynamic field and flag for IP reassembly incomplete case.
> >>> + */
> >>> +__rte_internal
> >>> +int
> >>> +rte_eth_ip_reass_dynfield_register(int *field_offset, int *flag);
> >>> +
> >>>
> >>>    /*
> >>>     * Legacy ethdev API used internally by drivers.
> >>> diff --git a/lib/ethdev/rte_ethdev.c b/lib/ethdev/rte_ethdev.c
> >>> index 88ca4ce867..48367dbec1 100644
> >>> --- a/lib/ethdev/rte_ethdev.c
> >>> +++ b/lib/ethdev/rte_ethdev.c
> >>> @@ -6567,6 +6567,34 @@ rte_eth_ip_reassembly_conf_set(uint16_t
> >> port_id,
> >>>    		       (*dev->dev_ops->ip_reassembly_conf_set)(dev, conf));
> >>>    }
> >>>
> >>> +int
> >>> +rte_eth_ip_reass_dynfield_register(int *field_offset, int *flag_offset)
> >>> +{
> >>> +	static const struct rte_mbuf_dynfield field_desc = {
> >>> +		.name = RTE_MBUF_DYNFIELD_IP_REASS_NAME,
> >>> +		.size = sizeof(rte_eth_ip_reass_dynfield_t),
> >>> +		.align = __alignof__(rte_eth_ip_reass_dynfield_t),
> >>> +	};
> >>> +	static const struct rte_mbuf_dynflag ip_reass_dynflag = {
> >>> +		.name =
> >> RTE_MBUF_DYNFLAG_IP_REASS_INCOMPLETE_NAME,
> >>> +	};
> >>> +	int offset;
> >>> +
> >>> +	offset = rte_mbuf_dynfield_register(&field_desc);
> >>> +	if (offset < 0)
> >>> +		return -1;
> >>> +	if (field_offset != NULL)
> >>> +		*field_offset = offset;
> >>> +
> >>> +	offset = rte_mbuf_dynflag_register(&ip_reass_dynflag);
> >>> +	if (offset < 0)
> >>> +		return -1;
> >>> +	if (flag_offset != NULL)
> >>> +		*flag_offset = offset;
> >>> +
> >>> +	return 0;
> >>> +}
> >>> +
> >>
> >> How mandatory is this field for the feature?
> >>
> >> If 'rte_eth_ip_reass_dynfield_register()' fails, what PMD should do?
> >> Should this API called before 'rte_eth_ip_reassembly_capability_get()' and
> >> if registering dnyfield fails should PMD return feature as not supported?
> >
> > Dynfield is added for the error/ incomplete reassembly case.
> > If the dynfield is not registered, the feature can work well for success
> scenarios.
> > Dynfield registration is responsibility of PMD and it is upto the driver to decide
> > when to set the dynfield. The registration can be done in conf_set() API.
> >
> >>
> >> Can you please describe this dependency, preferable in the
> >> 'rte_eth_ip_reassembly_capability_get()' doxygen comment?
> >
> > Capability get is not a place where the feature is enabled.
> > Dynfield should be registered only in case the feature is enabled.
> > I will add following line in conf_set() doxygen comment.
> >
> > The PMD should call 'rte_eth_ip_reass_dynfield_register()' when
> > the feature is enabled and return error if dynfield is not registered.
> > Dynfield is needed to give packets back to the application in case the
> > reassembly is not complete.
> >
> 
> Can you also clarify what PMD should do related to the ip reassembly feature
> when registering dynfield fails? Should it keep the feature enabled or disabled?
> 
> This will also clarify for the application, if application detects that
> 'RTE_MBUF_DYNFIELD_IP_REASS_NAME' is not registered how it should
> behave?
> Ignore it? Fail? Disable ip reassembly?

The PMD can return error in the conf_set API, if dynfield is not successfully
registered. Or in case of inline IPsec, the PMD can return the error while
creating inline security session.

Hence the application will get to know if the dynfield is successfully configured
Or not.
If the dynfield is not configured, PMD will return configuration error
(either in conf_set or in security_session_create) and feature
will not be enabled.