netdev - Re: [PATCH net] igmp: fix byte order in /proc/net/igmp output

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Message-Id: <201605041336.u44DaCGZ029899@d06av12.portsmouth.uk.ibm.com>
Date:	Wed, 4 May 2016 13:35:51 +0000
From:	"Evgeny Cherkashin" <Eugene.Crosser@...ibm.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	crosser@...rage.org, netdev@...r.kernel.org
Subject: Re: [PATCH net] igmp: fix byte order in /proc/net/igmp output

-----Eric Dumazet <eric.dumazet@...il.com> wrote: -----

>To: Evgeny Cherkashin/Russia/IBM@...RU
>From: Eric Dumazet <eric.dumazet@...il.com>
>Date: 2016-05-04 16:13
>Cc: crosser@...rage.org, netdev@...r.kernel.org
>Subject: Re: [PATCH net] igmp: fix byte order in /proc/net/igmp
>output
>
>On Wed, 2016-05-04 at 14:11 +0200, Eugene Crosser wrote:
>> /proc/net/igmp is a readonly attribute that shows multicast groups
>> to which different network interfaces are subscribed. Among other
>> things, it displays `multiaddr` which is a 32 bit
>network-byte-order
>> field, in hexadecimal format. Prior to this patch, the field was
>> displayed as an integer, resulting in reverse byte order on little
>> endian architectures. This patch converts it with ntohl() for
>display
>> the same way as this is done for the /proc/net/mcfilter attribute.
>> 
>> The patch changes (corrects) user-visible behaviour.
>> 
>> Signed-off-by: Eugene Crosser <Eugene.Crosser@...ibm.com>
>> ---
>>  net/ipv4/igmp.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
>> index b3086cf..f9d2139 100644
>> --- a/net/ipv4/igmp.c
>> +++ b/net/ipv4/igmp.c
>> @@ -2722,7 +2722,7 @@ static int igmp_mc_seq_show(struct seq_file
>*seq, void *v)
>>  		delta = im->timer.expires - jiffies;
>>  		seq_printf(seq,
>>  			   "\t\t\t\t%08X %5d %d:%08lX\t\t%d\n",
>> -			   im->multiaddr, im->users,
>> +			   ntohl(im->multiaddr), im->users,
>>  			   im->tm_running,
>>  			   im->tm_running ? jiffies_delta_to_clock_t(delta) : 0,
>>  			   im->reporter);
>
>
>I do not believe we can change this. This is unfortunately too late.
>
>/proc/net/tcp has the same 'issue' or if you prefer, well known
>behavior.
>
>Such change would break basically all /proc/net/igmp users.

I understand that. It is unfortunate though that the byte order is not _just_ wrong, it's _different_ on BE and LE machines...
Oh well.

Thanks,

Eugene