netdev - Re: [PATCH] printk: Let %pR handle NULL pointers

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Date:	Sun, 04 Jan 2009 10:31:26 +0100
From:	Johannes Berg <johannes@...solutions.net>
To:	Valdis.Kletnieks@...edu
Cc:	Trent Piepho <xyzzy@...akeasy.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Harvey Harrison <harvey.harrison@...il.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] printk: Let %pR handle NULL pointers

On Sun, 2009-01-04 at 00:14 -0500, Valdis.Kletnieks@...edu wrote:
> On Sat, 03 Jan 2009 21:02:15 PST, Trent Piepho said:
> > resource pointer.  Maybe "[]" or "[-]" would be better?  A null MAC address
> > could be ":::::" or "x:x:x:x:x:x".  "N.U.L.L" or "x.x.x.x" for a null IP4
> > address.  And so on.  So the printout looks nicer when a NULL pointer isn't
> > a bug.
> 
> Have to be careful for IPv6 addresses - '::' is a legal representation of
> an all-zeros address.  Also, N.U.L.L. may give indigestion to logfile parsers
> that are expecting a numeric value in the IP address.  It's however unclear
> whether we should pick something that doesn't have 3 periods in it, so it
> can't match, or whether *that* will give regexp-based logfile readers
> indigestion when they don't pick up an IP address where they expected...
> 
> Do we want the %pI6 format to do the multiple-zeros -> :: compression?

Eh, why ever care? We aren't passing NULL pointers in, hopefully, or the
code was crashing, at least before the conversion... So as long as we're
careful adding new users, I don't see a problem with not handling NULL.

FWIW, I'd think for MAC addresses there are multiple possible
interpretations, some wireless code assumes broadcast for NULL, and I'm
sure there are others like all-zeroes.

johannes

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