From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH net-next] sockopt: Change getsockopt() of
 SO_BINDTODEVICE to return an interface name
Date: Thu, 01 Nov 2012 10:52:28 -0400 (EDT)
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From: Andi Kleen <andi@firstfloor.org>
Date: Wed, 31 Oct 2012 13:47:01 -0700

> Brian Haley <brian.haley@hp.com> writes:
> 
>> Instead of having the getsockopt() of SO_BINDTODEVICE return an index, which
>> will then require another call like if_indextoname() to get the actual interface
>> name, have it return the name directly.
>>
>> This also matches the existing man page description on socket(7) which mentions
>> the argument being an interface name.
>>
>> If the value has not been set, zero is returned and optlen will be set to zero
>> to indicate there is no interface name present.
> 
> That will break all existing programs using the return value, right?
> Better to fix the manpage

It never returned a value before, you could not getsockopt() on
SO_BINDTODEVICE previously.