[SCSI] lib: add generic helper to print sizes rounded to the correct SI range

This patch adds the ability to print sizes in either units of 10^3 (SI)
or 2^10 (Binary) units.  It rounds up to three significant figures and
can be used for either memory or storage capacities.

Oh, and I'm fully aware that 64 bits is only 16EiB ... the Zetta and
Yotta units are added for future proofing against the day we have 128
bit computers ...

[fujita.tomonori@lab.ntt.co.jp: fix missed unsigned long long cast]
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

include/linux/string_helpers.h

+#ifndef _LINUX_STRING_HELPERS_H_
+#define _LINUX_STRING_HELPERS_H_
+
+#include <linux/types.h>
+
+/* Descriptions of the types of units to
+ * print in */
+enum string_size_units {
+	STRING_UNITS_10,	/* use powers of 10^3 (standard SI) */
+	STRING_UNITS_2,		/* use binary powers of 2^10 */
+};
+
+int string_get_size(u64 size, enum string_size_units units,
+		    char *buf, int len);
+
+#endif

lib/Makefile

@@ -19,7 +19,8 @@ lib-$(CONFIG_SMP) += cpumask.o
 lib-y	+= kobject.o kref.o klist.o
 
 obj-y += bcd.o div64.o sort.o parser.o halfmd4.o debug_locks.o random32.o \
-	 bust_spinlocks.o hexdump.o kasprintf.o bitmap.o scatterlist.o
+	 bust_spinlocks.o hexdump.o kasprintf.o bitmap.o scatterlist.o \
+	 string_helpers.o
 
 ifeq ($(CONFIG_DEBUG_KOBJECT),y)
 CFLAGS_kobject.o += -DDEBUG

lib/string_helpers.c

+/*
+ * Helpers for formatting and printing strings
+ *
+ * Copyright 31 August 2008 James Bottomley
+ */
+#include <linux/kernel.h>
+#include <linux/math64.h>
+#include <linux/module.h>
+#include <linux/string_helpers.h>
+
+/**
+ * string_get_size - get the size in the specified units
+ * @size:	The size to be converted
+ * @units:	units to use (powers of 1000 or 1024)
+ * @buf:	buffer to format to
+ * @len:	length of buffer
+ *
+ * This function returns a string formatted to 3 significant figures
+ * giving the size in the required units.  Returns 0 on success or
+ * error on failure.  @buf is always zero terminated.
+ *
+ */
+int string_get_size(u64 size, const enum string_size_units units,
+		    char *buf, int len)
+{
+	const char *units_10[] = { "B", "KB", "MB", "GB", "TB", "PB",
+				   "EB", "ZB", "YB", NULL};
+	const char *units_2[] = {"B", "KiB", "MiB", "GiB", "TiB", "PiB",
+				 "EiB", "ZiB", "YiB", NULL };
+	const char **units_str[] = {
+		[STRING_UNITS_10] =  units_10,
+		[STRING_UNITS_2] = units_2,
+	};
+	const int divisor[] = {
+		[STRING_UNITS_10] = 1000,
+		[STRING_UNITS_2] = 1024,
+	};
+	int i, j;
+	u64 remainder = 0, sf_cap;
+	char tmp[8];
+
+	tmp[0] = '\0';
+
+	for (i = 0; size > divisor[units] && units_str[units][i]; i++)
+		remainder = do_div(size, divisor[units]);
+
+	sf_cap = size;
+	for (j = 0; sf_cap*10 < 1000; j++)
+		sf_cap *= 10;
+
+	if (j) {
+		remainder *= 1000;
+		do_div(remainder, divisor[units]);
+		snprintf(tmp, sizeof(tmp), ".%03lld",
+			 (unsigned long long)remainder);
+		tmp[j+1] = '\0';
+	}
+
+	snprintf(buf, len, "%lld%s%s", (unsigned long long)size,
+		 tmp, units_str[units][i]);
+
+	return 0;
+}
+EXPORT_SYMBOL(string_get_size);