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Date: Thu, 17 Nov 2022 00:11:30 +0100
From: Stefano Brivio <sbrivio@redhat.com>
To: David Gibson <david@gibson.dropbear.id.au>
Subject: Re: [PATCH 05/32] tcp: Better helpers for converting between
connection pointer and index
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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 [...]
> + */
> +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.
--
Stefano