Re: [PATCH v2 07/11] flow: Introduce 'sidx' type to represent one side of one flow

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Nov 29, 2023 at 03:32:32PM +0100, Stefano Brivio wrote:
> On Mon, 27 Nov 2023 10:33:44 +1100
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > In a number of places, we use indices into the flow table to identify a
> > specific flow.  We also have cases where we need to identify a particular
> > side of a particular flow, and we expect those to become more common as
> > we generalise the flow table to cover more things.
> > 
> > To assist with that, introduces flow_sidx_t, an index type which identifies
> > a specific side of a specific flow in the table.
> > 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  flow.h       | 13 +++++++++++++
> >  flow_table.h | 36 ++++++++++++++++++++++++++++++++++++
> >  2 files changed, 49 insertions(+)
> > 
> > diff --git a/flow.h b/flow.h
> > index b6da516..3c90bbd 100644
> > --- a/flow.h
> > +++ b/flow.h
> > @@ -39,6 +39,19 @@ struct flow_common {
> >  #define FLOW_TABLE_PRESSURE		30	/* % of FLOW_MAX */
> >  #define FLOW_FILE_PRESSURE		30	/* % of c->nofile */
> >  
> > +/**
> > + * struct flow_sidx - ID for one side of a specific flow
> > + * @side:	Side referenced (0 or 1)
> > + * @flow:	Index of flow referenced
> > + */
> > +typedef struct flow_sidx {
> 
> Implying my usual argument :) ...is there any advantage over using this
> simply as a struct?

So, usually I too would prefer to use a struct as a struct, without a
typedef.  The reason I'm doing differently here, is that I want to
emphasise that for many purposes this can be treated like an index, in
particular that it's small and trivially copyable.  In particular it
should be passed by value, passing by reference would be silly.
That's kind of the opposite of what one tends to be conveying by
reminding users that they're working with a struct.

> 
> > +	int		side :1;
> > +	unsigned	flow :FLOW_INDEX_BITS;
> > +} flow_sidx_t;
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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