linux-kernel - Re: [PATCH] tools lib traceevent: Add support for IP address formats

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Message-ID: <549351A7.9040408@gmail.com>
Date:	Thu, 18 Dec 2014 15:13:59 -0700
From:	David Ahern <dsahern@...il.com>
To:	Valdis.Kletnieks@...edu
CC:	acme@...nel.org, linux-kernel@...r.kernel.org,
	Namhyung Kim <namhyung@...nel.org>,
	Jiri Olsa <jolsa@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] tools lib traceevent: Add support for IP address formats

On 12/18/14 2:45 PM, Valdis.Kletnieks@...edu wrote:
> On Thu, 18 Dec 2014 08:10:43 -0700, David Ahern said:
>> Adds helper for following kernel formats:
>>    %pi4 print an IPv4 address with leading zeros
>>    %pI4 print an IPv4 address without leading zeros
>>    %pi6 print an IPv6 address without colons
>>    %pI6 print an IPv6 address with colons
>>    %pI6c print an IPv6 address with colons
>>    %pISpc print an IP address from a sockaddr
>
> The description for %pI6C in the changelog doesn't match the code:
>
>> + * %pI6c  print an IPv6 address in compressed form with colons
>
> Threw me for a loop for a while trying to figure out how pI6 and pI6c were
> different, till I read the code...
>

Per Documentation/printk-formats.txt:

   %pI6    0001:0002:0003:0004:0005:0006:0007:0008
   %pi6    00010002000300040005000600070008
   %pI6c   1:2:3:4:5:6:7:8

   For printing IPv6 network-order 16-bit hex addresses. The 'I6' and 'i6'
   specifiers result in a printed address with ('I6') or without ('i6')
   colon-separators. Leading zeros are always used.

   The additional 'c' specifier can be used with the 'I' specifier to
   print a compressed IPv6 address as described by
         http://tools.ietf.org/html/rfc5952



I do see two mistakes in my patch -- use of 'c' and 'S' requires 'I'. 
After that the code that prints pI6c is a slightly modified version of 
what is in lib/vsprintf.c so the output between in-kernel tracing (cat 
trace_pipe) should match perf-script output. Compare 
ip6_compressed_string() in lib/vsprintf.c to print_ip6c_addr() in this 
patch.

Are you seeing something different?

David

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