Re: [PATCH 6/6] flow, tcp: Add logging helpers for connection related messages

[Stefano Brivio <sbrivio@redhat.com>]

On Thu, 23 Nov 2023 13:36:29 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> Most of the messages logged by the TCP code (be they errors, debug or
> trace messages) are related to a specific connection / flow.  We're fairly
> consistent about prefixing these with the type of connection and the
> connection / flow index.  However there are a few places where we put the
> index later in the message or omit it entirely.  The template with the
> prefix is also a little bulky to carry around for every message,
> particularly for spliced connections.
> 
> To help keep this consistent, introduce some helpers to log messages
> linked to a specific flow.  It takes the flow as a parameter and adds a
> uniform prefix to each message.  This makes things slightly neater now, but
> more importantly will help keep formatting consistent as we add more things
> to the flow table.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  flow.c       | 21 ++++++++++++++
>  flow.h       | 14 +++++++++
>  tcp.c        | 81 ++++++++++++++++++++++++----------------------------
>  tcp_splice.c | 61 +++++++++++++++++----------------------
>  4 files changed, 99 insertions(+), 78 deletions(-)
> 
> diff --git a/flow.c b/flow.c
> index 0fff119..cb2cf62 100644
> --- a/flow.c
> +++ b/flow.c
> @@ -64,3 +64,24 @@ void flow_table_compact(struct ctx *c, union flow *hole)
>  
>  	memset(from, 0, sizeof(*from));
>  }
> +
> +/** flow_log_ - Log flow-related message
> + * @f:		flow the message is related to
> + * @pri:	Log priority
> + * @fmt:	Format string
> + * @...:	printf-arguments
> + *
> + * @fmt must include an initial "%s" to expand to the prefix we generate
> + * (typically added by the flow_log() macro).

I don't understand how it does that -- flow_log() seems to just pass
__VA_ARGS__ through?

> + */
> +void flow_log_(const struct flow_common *f, int pri, const char *fmt, ...)
> +{
> +	char msg[BUFSIZ];
> +	va_list args;
> +
> +	va_start(args, fmt);
> +	(void)vsnprintf(msg, sizeof(msg), fmt, args);
> +	va_end(args);
> +
> +	logmsg(pri, "Flow %u (%s): %s", flow_idx(f), FLOW_TYPE(f), msg);
> +}
> diff --git a/flow.h b/flow.h
> index 9f49195..b6da516 100644
> --- a/flow.h
> +++ b/flow.h
> @@ -43,4 +43,18 @@ union flow;
>  
>  void flow_table_compact(struct ctx *c, union flow *hole);
>  
> +void flow_log_(const struct flow_common *f, int pri, const char *fmt, ...)
> +	__attribute__((format(printf, 3, 4)));
> +
> +#define flow_log(f_, pri, ...)	flow_log_(&(f_)->f, (pri), __VA_ARGS__)
> +
> +#define flow_dbg(f, ...)	flow_log((f), LOG_DEBUG, __VA_ARGS__)
> +#define flow_err(f, ...)	flow_log((f), LOG_ERR, __VA_ARGS__)
> +
> +#define flow_trace(f, ...)						\
> +	do {								\
> +		if (log_trace)						\
> +			flow_dbg((f), __VA_ARGS__);			\
> +	} while (0)
> +
>  #endif /* FLOW_H */

-- 
Stefano