Re: [PATCH v7 1/2] node: add global node mbuf dynfield

[Nitin Saxena]

Hi Stephen,


On Thu, Jun 26, 2025 at 7:29 PM Stephen Hemminger
<step...@networkplumber.org> wrote:
>
> On Thu, 19 Jun 2025 21:14:49 +0530
> Nitin Saxena <nsax...@marvell.com> wrote:
>
> > +#ifndef RTE_NODE_MBUF_PERSISTENT_FIELDS_SIZE
> > +/** Size of persistent mbuf fields */
> > +#define RTE_NODE_MBUF_PERSISTENT_FIELDS_SIZE          (0)
> > +#endif /* RTE_NODE_MBUF_PERSISTENT_FIELDS_SIZE */
> > +
> > +#ifndef RTE_NODE_MBUF_OVERLOADABLE_FIELDS_SIZE
> > +/** Size of overloadable mbuf fields */
> > +#define RTE_NODE_MBUF_OVERLOADABLE_FIELDS_SIZE        (8)
> > +#endif /* RTE_NODE_MBUF_OVERLOADABLE_FIELDS_SIZE */
> > +
> > +/** Size of node mbuf dynamic field */
> > +#define RTE_NODE_MBUF_DYNFIELD_SIZE     \
> > +     (RTE_NODE_MBUF_PERSISTENT_FIELDS_SIZE + 
> > RTE_NODE_MBUF_OVERLOADABLE_FIELDS_SIZE)
> > +
> > +/**
> > + * Node mbuf overloadable data.
> > + *
> > + * Out-of-tree nodes can repurpose overloadable fields via
> > + * rte_node_mbuf_overload_fields_get(mbuf). Overloadable fields are not
> > + * preserved and typically can be used with-in two adjacent nodes in the 
> > graph.
> > + */
> > +typedef struct rte_node_mbuf_overload_fields {
> > +     union {
> > +             uint8_t data[RTE_NODE_MBUF_OVERLOADABLE_FIELDS_SIZE];
> > +     };
> > +} rte_node_mbuf_overload_fields_t;
>
> Having a blank scratchpad rather than a real defined structure means you
> lose any type checking or potential overflow checking.

Patchset-1 creates a blank scratchpad but patchset-2 adds following
fields when added field is used in ip4/ip6 nodes
So idea is to add relevant structures as and when they are used

 diff --git a/lib/node/rte_node_mbuf_dynfield.h
b/lib/node/rte_node_mbuf_dynfield.h
 index 1069c07d44..045c13e352 100644
 --- a/lib/node/rte_node_mbuf_dynfield.h
 +++ b/lib/node/rte_node_mbuf_dynfield.h
 @@ -46,6 +46,15 @@ extern "C" {
   */
  typedef struct rte_node_mbuf_overload_fields {
  >------union {
+>------>-------/* Following fields used by ip[4|6]-lookup ->
ip[4|6]-rewrite nodes */
+>------>-------union {
+>------>------->-------struct {
+>------>------->------->-------uint16_t nh;
+>------>------->------->-------uint16_t ttl;
+>------>------->------->-------uint32_t cksum;
+>------>------->-------};
+>------>------->-------uint64_t u;
+>------>-------};
>------>-------uint8_t data[RTE_NODE_MBUF_OVERLOADABLE_FIELDS_SIZE];
>------};
} rte_node_mbuf_overload_fields_t;