linux-kernel - [PATCH] strings: helper for maximum decimal encoding of an unsigned integer

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Message-ID: <20120821212910.GD18637@fieldses.org>
Date:	Tue, 21 Aug 2012 17:29:10 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	linux-kernel@...r.kernel.org
Cc:	Jim Rees <rees@...ch.edu>
Subject: [PATCH] strings: helper for maximum decimal encoding of an
 unsigned integer

From: "J. Bruce Fields" <bfields@...hat.com>

I've seen a couple examples recently where we've gotten this wrong.
Maybe something like this would help?  Is there some better way?

(Approximation due to Jim Rees).

Signed-off-by: J. Bruce Fields <bfields@...hat.com>
---
 include/linux/string.h |    6 ++++++
 net/sunrpc/cache.c     |    2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/linux/string.h b/include/linux/string.h
index ffe0442..d4809b7 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -126,6 +126,12 @@ extern void argv_free(char **argv);
 extern bool sysfs_streq(const char *s1, const char *s2);
 extern int strtobool(const char *s, bool *res);
 
+/*
+ * length of the decimal representation of an unsigned integer.  Just an
+ * approximation, but it's right for types of size 1 to 36 bytes:
+ */
+#define base10len(i) (sizeof(i) * 24 / 10 + 1)
+
 #ifdef CONFIG_BINARY_PRINTF
 int vbin_printf(u32 *bin_buf, size_t size, const char *fmt, va_list args);
 int bstr_printf(char *buf, size_t size, const char *fmt, const u32 *bin_buf);
diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
index 2afd2a8..1dcd2b3 100644
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -1409,7 +1409,7 @@ static ssize_t read_flush(struct file *file, char __user *buf,
 			  size_t count, loff_t *ppos,
 			  struct cache_detail *cd)
 {
-	char tbuf[20];
+	char tbuf[base10len(long) + 2];
 	unsigned long p = *ppos;
 	size_t len;
 
-- 
1.7.9.5

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