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

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Date:	Sat, 3 Jan 2009 09:10:40 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Trent Piepho <xyzzy@...akeasy.org>
cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Harvey Harrison <harvey.harrison@...il.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] printk: Let %pR handle NULL pointers

On Sat, 3 Jan 2009, Trent Piepho wrote:
>
> Have %pR print "[NULL]" for the resource range when passed a NULL pointer.

Wouldn't it be much nicer to just do it for _all_ pointer types?

IOW, a patch more like the appended.

Also, I'm not 100% sure that "[NULL]" is the right thing to print. Not 
that I know if there's anything better. Testing glibc, it prints "(nil)" 
for a NULL string (%s) and "(null)" for a NULL pointer (%p). Which makes 
no more sense than anything else, but maybe we could make the NULL %p case 
at least match that if for no other reason than the fact that it would 
match _something_.

Added the other people who added %pX modifiers to the cc - I guess the 
networking people probably never have NULL pointers there anyway, but 
maybe they have opinions.

		Linus

---
 lib/vsprintf.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 3b77702..4df1884 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -661,6 +661,9 @@ static char *ip4_addr_string(char *buf, char *end, u8 *addr, int field_width,
  */
 static char *pointer(const char *fmt, char *buf, char *end, void *ptr, int field_width, int precision, int flags)
 {
+	if (!ptr)
+		return string(buf, end, "[NULL]", field_width, precision, flags);
+
 	switch (*fmt) {
 	case 'F':
 		ptr = dereference_function_descriptor(ptr);
--
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