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

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Message-ID: <Pine.LNX.4.58.0901041232460.25853@shell2.speakeasy.net>
Date:	Sun, 4 Jan 2009 12:41:49 -0800 (PST)
From:	Trent Piepho <xyzzy@...akeasy.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
cc:	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>
Subject: Re: [PATCH] printk: Let %pR handle NULL pointers

On Sun, 4 Jan 2009, Benjamin Herrenschmidt wrote:
> > I thought of doing that too, but then all the various %pX formats would all
> > have to print the same for NULL pointers.  For instance a resource prints
> > out like "[0x1000-0x100f]", so I chose "[NULL]" for printing a null
> > 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.
>
> And how often is that ?

For resource pointers it's not uncommon.  There are many cases when it's perfectly
ok for a resource pointer to be null, e.g. res->parent is often null, pci devices
and busses don't usually have all possible ranges, etc.  It nice to get decent info
printouts without having the check for NULL pointers.
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