Subject: Re: [net-next PATCH v1 01/11] net: flow_table: create interface for hw match/action tables

From: Simon Horman <[email-masked]>
Date: Tue, 6 Jan 2015 10:09:44 +0900

On Mon, Jan 05, 2015 at 04:45:50PM -0800, John Fastabend wrote:
> [...]
> 
> >>>+/**
> >>>+ * @struct net_flow_field_ref
> >>>+ * @brief uniquely identify field as header:field tuple
> >>>+ */
> >>>+struct net_flow_field_ref {
> >>>+    int instance;
> >>>+    int header;
> >>>+    int field;
> >>>+    int mask_type;
> >>>+    int type;
> >>>+    union {    /* Are these all the required data types */
> >>>+        __u8 value_u8;
> >>>+        __u16 value_u16;
> >>>+        __u32 value_u32;
> >>>+        __u64 value_u64;
> >>>+    };
> >>>+    union {    /* Are these all the required data types */
> >>>+        __u8 mask_u8;
> >>>+        __u16 mask_u16;
> >>>+        __u32 mask_u32;
> >>>+        __u64 mask_u64;
> >>>+    };
> >>>+};
> >>
> >>Does it make sense to write this as follows?
> >
> >Yes. I'll make this update it helps make it clear value/mask pairs are
> >needed.
> >
> >>
> >>union {
> >>         struct {
> >>                 __u8 value_u8;
> >>                 __u8 mask_u8;
> >>         };
> >>         struct {
> >>                 __u16 value_u16;
> >>                 __u16 mask_u16;
> >>         };
> >>         ...
> >>};
> 
> Another thought is to pull this entirely out of the structure and hide
> it from the UAPI so we can add more value/mask types as needed without
> having to spin versions of net_flow_field_ref. On the other hand I've
> been able to fit all my fields in these types so far and I can't think
> of any additions we need at the moment.

FWIW, I think it would be cleaner to break both field_ref and action_args
out into attributes and not expose the structures to user-space. But
perhaps there is an advantage to dealing with structures directly that
I am missing.