[PATCH] Add parse_integer() (replacement for simple_strto*())

[Alexey Dobriyan]

kstrto*() and kstrto*_from_user() family of functions were added
help with parsing one integer written as string to proc/sysfs/debugfs
files and pass it elsewhere. But they have a limitation: string passed
must end with \0 or \n\0. There are enough places where kstrto*()
functions can't be used because of this limitation. Trivial example:
parse "%u.%u".

Currently the only way to parse everything is simple_strto*() family of
functions. But they are suboptimal:
* they do not detect overflow,
* there are only 2(4) of them -- long and "long long" version.
  This leads to silent truncation in the most simple case:

	val = strtoul(s, NULL, 0);

* half of the people think that "char **endp" argument is necessary and
  add unnecessary variable.

OpenBSD people, fed up with how complex correct integer parsing is, added
strtonum(3) to fixup for deficiencies of libc-style integer parsing:
http://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man3/strtonum.3?query=strtonum&arch=i386

It'd be OK to copy that but it relies on "errno" and fixed strings as
error-reporting channel which I think is not OK for kernel.
strtonum() also doesn't report number of characted consumed.

What to do?

Enter parse_integer().

	int parse_integer(const char *s, unsigned int base, T *val);

Rationale:

* parse_integer() is exactly 1 (one) interface not 2 or many,
  one for each type.
* parse_integer() reports -E errors reliably in a canonical kernel way:

	rv = parse_integer(str, 10, &val);
	if (rv < 0)
		return rv;

* parse_integer() writes result only if there were no errors, at least
  one digit was consumed.
* parse_integer doesn't mix error reporting channel and value channel,
  it does mix error and number-of-character-consumed channel, though.

* parse_integer() reports number of characters consumed, makes parsing
  multiple values easy:

	rv = parse_integer(str, 0, &val1);
	if (rv < 0)
		return rv;
	s += rv;
	if (s != '.')
		return -EINVAL;
	rv = parse_integer(str, 0, &val2);
	if (rv < 0)
		return rv;
	if (str[rv] != '\0')
		return -EINVAL;

There are several deficiencies in parse_integer() compared to strto*():
* can't be used in initializers:

	const T x = strtoul();

* can't be used with bitfields,
* can't be used in experessions:

	x = strtol() * 1024;
	x = y = strtol() * 1024;
	x += strtol();

In defense of parse_integer() all I can say, is that using strtol() in
expression or initializer promotes no error checking and thus probably
should not be encouraged in C, language with no built-in error checking
anyway.

The amount of "x = y = strtol()" expressions in kernel is very small.
The amount of direct usage in expression is not small, but can be
counted as an acceptable loss.

Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx>
---

 include/linux/kernel.h |   72 +++++++++++++++++++
 lib/Makefile           |    1 
 lib/kstrtox.c          |   27 +------
 lib/parse-integer.c    |  180 +++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 257 insertions(+), 23 deletions(-)

--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -251,6 +251,78 @@ void do_exit(long error_code)
 void complete_and_exit(struct completion *, long)
 	__noreturn;
 
+/*
+ * int parse_integer(const char *s, unsigned int base, T *val);
+ *
+ * Convert integer string representation to an integer.
+ * If an integer doesn't fit into specified type, -E is returned.
+ *
+ * Conversion to signed integer accepts sign "-".
+ * Conversion to an unsigned integer doesn't accept sign "-".
+ *
+ * Radix 0 means autodetection: leading "0x" implies radix 16,
+ * leading "0" implies radix 8, otherwise radix is 10.
+ * Autodetection hints work after optional sign, but not before.
+ *
+ * If -E is returned, result is not touched.
+ *
+ * "T = char" case is not supported because -f{un,}signed-char can silently
+ * change range of accepted values.
+ */
+#define parse_integer(s, base, val)	\
+({					\
+	const char *_s = (s);		\
+	unsigned int _base = (base);	\
+	typeof(val) _val = (val);	\
+					\
+	__builtin_choose_expr(						\
+	__builtin_types_compatible_p(typeof(_val), signed char *),	\
+	_parse_integer_sc(_s, _base, (void *)_val),			\
+	__builtin_choose_expr(						\
+	__builtin_types_compatible_p(typeof(_val), unsigned char *),	\
+	_parse_integer_uc(_s, _base, (void *)_val),			\
+	__builtin_choose_expr(						\
+	__builtin_types_compatible_p(typeof(_val), short *),		\
+	_parse_integer_s(_s, _base, (void *)_val),			\
+	__builtin_choose_expr(						\
+	__builtin_types_compatible_p(typeof(_val), unsigned short *),	\
+	_parse_integer_us(_s, _base, (void *)_val),			\
+	__builtin_choose_expr(						\
+	__builtin_types_compatible_p(typeof(_val), int *),		\
+	_parse_integer_i(_s, _base, (void *)_val),			\
+	__builtin_choose_expr(						\
+	__builtin_types_compatible_p(typeof(_val), unsigned int *),	\
+	_parse_integer_u(_s, _base, (void *)_val),			\
+	__builtin_choose_expr(						\
+	__builtin_types_compatible_p(typeof(_val), long *) && BITS_PER_LONG == 32,\
+	_parse_integer_i(_s, _base, (void *)_val),			\
+	__builtin_choose_expr(						\
+	__builtin_types_compatible_p(typeof(_val), long *) && BITS_PER_LONG == 64,\
+	_parse_integer_ll(_s, _base, (void *)_val),			\
+	__builtin_choose_expr(						\
+	__builtin_types_compatible_p(typeof(_val), unsigned long *) && BITS_PER_LONG == 32,\
+	_parse_integer_u(_s, _base, (void *)_val),			\
+	__builtin_choose_expr(						\
+	__builtin_types_compatible_p(typeof(_val), unsigned long *) && BITS_PER_LONG == 64,\
+	_parse_integer_ull(_s, _base, (void *)_val),			\
+	__builtin_choose_expr(						\
+	__builtin_types_compatible_p(typeof(_val), long long *),	\
+	_parse_integer_ll(_s, _base, (void *)_val),			\
+	__builtin_choose_expr(						\
+	__builtin_types_compatible_p(typeof(_val), unsigned long long *),\
+	_parse_integer_ull(_s, _base, (void *)_val),			\
+	_parse_integer_link_time_error()))))))))))));	\
+})
+int _parse_integer_sc(const char *s, unsigned int base, signed char *val);
+int _parse_integer_uc(const char *s, unsigned int base, unsigned char *val);
+int _parse_integer_s(const char *s, unsigned int base, short *val);
+int _parse_integer_us(const char *s, unsigned int base, unsigned short *val);
+int _parse_integer_i(const char *s, unsigned int base, int *val);
+int _parse_integer_u(const char *s, unsigned int base, unsigned int *val);
+int _parse_integer_ll(const char *s, unsigned int base, long long *val);
+int _parse_integer_ull(const char *s, unsigned int base, unsigned long long *val);
+void _parse_integer_link_time_error(void);
+
 /* Internal, do not use. */
 int __must_check _kstrtoul(const char *s, unsigned int base, unsigned long *res);
 int __must_check _kstrtol(const char *s, unsigned int base, long *res);
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -32,6 +32,7 @@ obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
 obj-y += hexdump.o
 obj-$(CONFIG_TEST_HEXDUMP) += test-hexdump.o
 obj-y += kstrtox.o
+obj-y += parse-integer.o
 obj-$(CONFIG_TEST_BPF) += test_bpf.o
 obj-$(CONFIG_TEST_FIRMWARE) += test_firmware.o
 obj-$(CONFIG_TEST_KASAN) += test_kasan.o
--- a/lib/kstrtox.c
+++ b/lib/kstrtox.c
@@ -20,22 +20,6 @@
 #include <asm/uaccess.h>
 #include "kstrtox.h"
 
-const char *_parse_integer_fixup_radix(const char *s, unsigned int *base)
-{
-	if (*base == 0) {
-		if (s[0] == '0') {
-			if (_tolower(s[1]) == 'x' && isxdigit(s[2]))
-				*base = 16;
-			else
-				*base = 8;
-		} else
-			*base = 10;
-	}
-	if (*base == 16 && s[0] == '0' && _tolower(s[1]) == 'x')
-		s += 2;
-	return s;
-}
-
 /*
  * Convert non-negative integer string representation in explicitly given radix
  * to an integer.
@@ -86,14 +70,11 @@ unsigned int _parse_integer(const char *s, unsigned int base, unsigned long long
 static int _kstrtoull(const char *s, unsigned int base, unsigned long long *res)
 {
 	unsigned long long _res;
-	unsigned int rv;
+	int rv;
 
-	s = _parse_integer_fixup_radix(s, &base);
-	rv = _parse_integer(s, base, &_res);
-	if (rv & KSTRTOX_OVERFLOW)
-		return -ERANGE;
-	if (rv == 0)
-		return -EINVAL;
+	rv = parse_integer(s, base, &_res);
+	if (rv < 0)
+		return rv;
 	s += rv;
 	if (*s == '\n')
 		s++;
--- /dev/null
+++ b/lib/parse-integer.c
@@ -0,0 +1,180 @@
+/*
+ * See parse_integer().
+ *
+ * Individual dispatch functions in this file aren't supposed to be used
+ * directly and thus aren't advertised and documented despited being exported.
+ *
+ * Do not use any function in this file for any reason.
+ */
+#include <linux/ctype.h>
+#include <linux/errno.h>
+#include <linux/export.h>
+#include <linux/kernel.h>
+#include <linux/math64.h>
+#include <asm/bug.h>
+#include "kstrtox.h"
+
+const char *_parse_integer_fixup_radix(const char *s, unsigned int *base)
+{
+	if (*base == 0) {
+		if (s[0] == '0') {
+			if (_tolower(s[1]) == 'x' && isxdigit(s[2]))
+				*base = 16;
+			else
+				*base = 8;
+		} else
+			*base = 10;
+	}
+	if (*base == 16 && s[0] == '0' && _tolower(s[1]) == 'x')
+		s += 2;
+	BUG_ON(*base < 2 || *base > 16);
+	return s;
+}
+
+int _parse_integer_ull(const char *s, unsigned int base, unsigned long long *val)
+{
+	const char *s0 = s, *sd;
+	unsigned long long acc;
+
+	s = sd = _parse_integer_fixup_radix(s0, &base);
+	acc = 0;
+	while (*s != '\0') {
+		unsigned int d;
+
+		if ('0' <= *s && *s <= '9')
+			d = *s - '0';
+		else if ('a' <= _tolower(*s) && _tolower(*s) <= 'f')
+			d = _tolower(*s) - 'a' + 10;
+		else
+			break;
+		if (d >= base)
+			break;
+		/* Overflow can't happen early enough. */
+		if ((acc >> 60) && acc > div_u64(ULLONG_MAX - d, base))
+			return -ERANGE;
+		acc = acc * base + d;
+		s++;
+	}
+	/* At least one digit has to be converted. */
+	if (s == sd)
+		return -EINVAL;
+	*val = acc;
+	/* Radix 1 is not supported otherwise returned length can overflow. */
+	return s - s0;
+}
+EXPORT_SYMBOL(_parse_integer_ull);
+
+int _parse_integer_ll(const char *s, unsigned int base, long long *val)
+{
+	unsigned long long tmp;
+	int rv;
+
+	if (*s == '-') {
+		rv = _parse_integer_ull(s + 1, base, &tmp);
+		if (rv < 0)
+			return rv;
+		if ((long long)-tmp >= 0)
+			return -ERANGE;
+		*val = -tmp;
+		return rv + 1;
+	} else {
+		rv = _parse_integer_ull(s, base, &tmp);
+		if (rv < 0)
+			return rv;
+		if ((long long)tmp < 0)
+			return -ERANGE;
+		*val = tmp;
+		return rv;
+	}
+}
+EXPORT_SYMBOL(_parse_integer_ll);
+
+int _parse_integer_u(const char *s, unsigned int base, unsigned int *val)
+{
+	unsigned long long tmp;
+	int rv;
+
+	rv = _parse_integer_ull(s, base, &tmp);
+	if (rv < 0)
+		return rv;
+	if (tmp != (unsigned int)tmp)
+		return -ERANGE;
+	*val = tmp;
+	return rv;
+}
+EXPORT_SYMBOL(_parse_integer_u);
+
+int _parse_integer_i(const char *s, unsigned int base, int *val)
+{
+	long long tmp;
+	int rv;
+
+	rv = _parse_integer_ll(s, base, &tmp);
+	if (rv < 0)
+		return rv;
+	if (tmp != (int)tmp)
+		return -ERANGE;
+	*val = tmp;
+	return rv;
+}
+EXPORT_SYMBOL(_parse_integer_i);
+
+int _parse_integer_us(const char *s, unsigned int base, unsigned short *val)
+{
+	unsigned long long tmp;
+	int rv;
+
+	rv = _parse_integer_ull(s, base, &tmp);
+	if (rv < 0)
+		return rv;
+	if (tmp != (unsigned short)tmp)
+		return -ERANGE;
+	*val = tmp;
+	return rv;
+}
+EXPORT_SYMBOL(_parse_integer_us);
+
+int _parse_integer_s(const char *s, unsigned int base, short *val)
+{
+	long long tmp;
+	int rv;
+
+	rv = _parse_integer_ll(s, base, &tmp);
+	if (rv < 0)
+		return rv;
+	if (tmp != (short)tmp)
+		return -ERANGE;
+	*val = tmp;
+	return rv;
+}
+EXPORT_SYMBOL(_parse_integer_s);
+
+int _parse_integer_uc(const char *s, unsigned int base, unsigned char *val)
+{
+	unsigned long long tmp;
+	int rv;
+
+	rv = _parse_integer_ull(s, base, &tmp);
+	if (rv < 0)
+		return rv;
+	if (tmp != (unsigned char)tmp)
+		return -ERANGE;
+	*val = tmp;
+	return rv;
+}
+EXPORT_SYMBOL(_parse_integer_uc);
+
+int _parse_integer_sc(const char *s, unsigned int base, signed char *val)
+{
+	long long tmp;
+	int rv;
+
+	rv = _parse_integer_ll(s, base, &tmp);
+	if (rv < 0)
+		return rv;
+	if (tmp != (signed char)tmp)
+		return -ERANGE;
+	*val = tmp;
+	return rv;
+}
+EXPORT_SYMBOL(_parse_integer_sc);
--
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