Re: [PATCH 05/32] tcp: Better helpers for converting between connection pointer and index

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

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On Thu, Nov 17, 2022 at 12:11:30AM +0100, Stefano Brivio wrote:
> On Wed, 16 Nov 2022 15:41:45 +1100
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > The macro CONN_OR_NULL() is used to look up connections by index with
> > bounds checking.  Replace it with an inline function, which means:
> >     - Better type checking
> >     - No danger of multiple evaluation of an @index with side effects
> > 
> > Also add a helper to perform the reverse translation: from connection
> > pointer to index.  Introduce a macro for this which will make later
> > cleanups easier and safer.
> 
> Ah, yes, much better, agreed. Just two things here:
> 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  tcp.c | 83 ++++++++++++++++++++++++++++++++---------------------------
> >  1 file changed, 45 insertions(+), 38 deletions(-)
> > 
> > diff --git a/tcp.c b/tcp.c
> > index d043123..4e56a6c 100644
> > --- a/tcp.c
> > +++ b/tcp.c
> > @@ -518,14 +518,6 @@ struct tcp_conn {
> >  	 (conn->events & (SOCK_FIN_RCVD | TAP_FIN_RCVD)))
> >  #define CONN_HAS(conn, set)	((conn->events & (set)) == (set))
> >  
> > -#define CONN(index)		(tc + (index))
> > -
> > -/* We probably don't want to use gcc statement expressions (for portability), so
> > - * use this only after well-defined sequence points (no pre-/post-increments).
> > - */
> > -#define CONN_OR_NULL(index)						\
> > -	(((int)(index) >= 0 && (index) < TCP_MAX_CONNS) ? (tc + (index)) : NULL)
> > -
> >  static const char *tcp_event_str[] __attribute((__unused__)) = {
> >  	"SOCK_ACCEPTED", "TAP_SYN_RCVD", "ESTABLISHED", "TAP_SYN_ACK_SENT",
> >  
> > @@ -705,6 +697,21 @@ static size_t tcp6_l2_flags_buf_bytes;
> >  /* TCP connections */
> >  static struct tcp_conn tc[TCP_MAX_CONNS];
> >  
> > +#define CONN(index)		(tc + (index))
> > +#define CONN_IDX(conn)		((conn) - tc)
> > +
> > +/** conn_at_idx() - Find a connection by index, if present
> > + * @index:	Index of connection to lookup
> > + *
> > + * Return:	Pointer to connection, or NULL if @index is out of bounds
> 
> Return: pointer [...]

Fixed.

> > + */
> > +static inline struct tcp_conn *conn_at_idx(int index)
> 
> The CONN_OR_NULL name made it very explicit that the pointer obtained
> there could be NULL. On the other hand I find conn_at_idx() more
> descriptive. But maybe conn_or_null() would be "safer". I don't really
> have a preference.

I see your point, but on balance I think I marginally prefer
conn_at_idx(), so I've left it.

-- 
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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