From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stephen Hemminger <shemminger@vyatta.com>
Subject: Re: [PATCH v2] iproute2: add support for tcp_metrics
Date: Tue, 2 Oct 2012 17:26:33 -0700
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Cc: Eric Dumazet <eric.dumazet@gmail.com>, netdev@vger.kernel.org
To: Julian Anastasov <ja@ssi.bg>
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On Wed, 3 Oct 2012 03:21:08 +0300 (EEST)
Julian Anastasov <ja@ssi.bg> wrote:

> 	Something like this in process_msg?:
> 
> case TCP_METRIC_RTT:
> 	fprintf(fp, "%lluus",
> 		((__u64) val * 1000) >> 3);
> 	break;
> case TCP_METRIC_RTTVAR:
> 	fprintf(fp, "%lluus",
> 		((__u64) val * 1000) >> 2);
> 	break;
> 
> 	And may be variant without __u64 should be fine?

Remember u64 is not always same as unsigned long long.
One safe way of handling this is:

#include <inttypes.h>
...
 
 case TCP_METRIC_RTT:
	fprintf(fp, "%"PRIu64"us",
 		((__u64) val * 1000) >> 3);
 	break;
 case TCP_METRIC_RTTVAR:
 	fprintf(fp, "%"PRIu64"us",
 		((__u64) val * 1000) >> 2);
 	break;

Also make sure metrics work independent of kernel HZ.