netdev - Re: IPv6 address printf format specifier

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Message-Id: <20090318.185826.221840814.davem@davemloft.net>
Date:	Wed, 18 Mar 2009 18:58:26 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	vladislav.yasevich@...com
Cc:	chuck.lever@...cle.com, netdev@...r.kernel.org
Subject: Re: IPv6 address printf format specifier

From: Vlad Yasevich <vladislav.yasevich@...com>
Date: Mon, 16 Mar 2009 13:13:00 -0400

> Chuck Lever wrote:
> > The NFS and RPC code in the kernel now uses the new printf format
> > specifier for IPv6 addresses.  In some cases, the generated address
> > string is sent out of the kernel (for example, it is used to build a
> > universal address for RPCB_SET requests, and used as the mon_name in
> > some SM_MON upcalls to our rpc.statd).
> > 
> > The problem is that outside the kernel, applications generally use
> > getnameinfo(3) or inet_ntop(3) to do this conversion.  The library
> > follows the RFC suggestion of shortening these address strings by
> > replacing the longest series of zeroes in the IPv6 address with "::".
> > 
> > Since the kernel doesn't do that, string comparisons don't work when
> > comparing address strings that came from our kernel.  Since these
> > address strings appear to other hosts (via the rpcbind registry) this
> > is, or could become, an interoperability issue for Linux.
> > 
> > How should I fix this?
> > 
> > 1.  Copy glibc's code to the printf logic for %pI6
> 
> I think this is the optimum solution.  This normalizes kernel output
> with that of user-space thus creating a uniform format.
> 
> My $0.02

Then you'll break cases where this string is output via
some /proc/ file or whatever and it expects the existing
behavior.

I don't think we can do this.
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