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

On Thu, 30 Nov 2023 11:37:40 +1100
David Gibson <david(a)gibson.dropbear.id.au> wrote:

...
  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(a)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(a)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. 
Hmm, that was exactly my "not hiding" point though. The day somebody
adds here:

	char mood[RLIMIT_STACK_VAL + 1]; /* list of side emojis */

the typedef makes it still apparently okay to pass by value. If it's a
struct, one surely has to check first.

...
  That's kind of the opposite of what one tends to
be conveying by
 reminding users that they're working with a struct. 
I see, but it's probably a matter of taste (passing structs by value
doesn't personally make me nervous).

-- 
Stefano