kfifo API type safety

This patch enhances the type safety for the kfifo API.  It is now safe
to put const data into a non const FIFO and the API will now generate a
compiler warning when reading from the fifo where the destination
address is pointing to a const variable.

As a side effect the kfifo_put() does now expect the value of an element
instead a pointer to the element.  This was suggested Russell King.  It
make the handling of the kfifo_put easier since there is no need to
create a helper variable for getting the address of a pointer or to pass
integers of different sizes.

IMHO the API break is okay, since there are currently only six users of
kfifo_put().

The code is also cleaner by kicking out the "if (0)" expressions.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Stefani Seibold <stefani@seibold.net>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 33 deletions

diff --git a/include/linux/kfifo.h b/include/linux/kfifo.h
index 10308c6a3d1c..552d51efb429 100644
--- a/include/linux/kfifo.h
+++ b/include/linux/kfifo.h
@@ -1,7 +1,7 @@
 /*
  * A generic kernel FIFO implementation
  *
- * Copyright (C) 2009/2010 Stefani Seibold <stefani@seibold.net>
+ * Copyright (C) 2013 Stefani Seibold <stefani@seibold.net>
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -67,9 +67,10 @@ struct __kfifo {
         union { \
                 struct __kfifo  kfifo; \
                 datatype        *type; \
+                const datatype  *const_type; \
                 char            (*rectype)[recsize]; \
                 ptrtype         *ptr; \
-                const ptrtype   *ptr_const; \
+                ptrtype const   *ptr_const; \
         }
 
 #define __STRUCT_KFIFO(type, size, recsize, ptrtype) \
@@ -386,16 +387,12 @@ __kfifo_int_must_check_helper( \
 #define kfifo_put(fifo, val) \
 ({ \
         typeof((fifo) + 1) __tmp = (fifo); \
-        typeof((val) + 1) __val = (val); \
+        typeof(*__tmp->const_type) __val = (val); \
         unsigned int __ret; \
-        const size_t __recsize = sizeof(*__tmp->rectype); \
+        size_t __recsize = sizeof(*__tmp->rectype); \
         struct __kfifo *__kfifo = &__tmp->kfifo; \
-        if (0) { \
-                typeof(__tmp->ptr_const) __dummy __attribute__ ((unused)); \
-                __dummy = (typeof(__val))NULL; \
-        } \
         if (__recsize) \
-                __ret = __kfifo_in_r(__kfifo, __val, sizeof(*__val), \
+                __ret = __kfifo_in_r(__kfifo, &__val, sizeof(__val), \
                         __recsize); \
         else { \
                 __ret = !kfifo_is_full(__tmp); \
@@ -404,7 +401,7 @@ __kfifo_int_must_check_helper( \
                         ((typeof(__tmp->type))__kfifo->data) : \
                         (__tmp->buf) \
                         )[__kfifo->in & __tmp->kfifo.mask] = \
-                                *(typeof(__tmp->type))__val; \
+                                (typeof(*__tmp->type))__val; \
                         smp_wmb(); \
                         __kfifo->in++; \
                 } \
@@ -415,7 +412,7 @@ __kfifo_int_must_check_helper( \
 /**
  * kfifo_get - get data from the fifo
  * @fifo: address of the fifo to be used
- * @val: the var where to store the data to be added
+ * @val: address where to store the data
  *
  * This macro reads the data from the fifo.
  * It returns 0 if the fifo was empty. Otherwise it returns the number
@@ -428,12 +425,10 @@ __kfifo_int_must_check_helper( \
 __kfifo_uint_must_check_helper( \
 ({ \
         typeof((fifo) + 1) __tmp = (fifo); \
-        typeof((val) + 1) __val = (val); \
+        typeof(__tmp->ptr) __val = (val); \
         unsigned int __ret; \
         const size_t __recsize = sizeof(*__tmp->rectype); \
         struct __kfifo *__kfifo = &__tmp->kfifo; \
-        if (0) \
-                __val = (typeof(__tmp->ptr))0; \
         if (__recsize) \
                 __ret = __kfifo_out_r(__kfifo, __val, sizeof(*__val), \
                         __recsize); \
@@ -456,7 +451,7 @@ __kfifo_uint_must_check_helper( \
 /**
  * kfifo_peek - get data from the fifo without removing
  * @fifo: address of the fifo to be used
- * @val: the var where to store the data to be added
+ * @val: address where to store the data
  *
  * This reads the data from the fifo without removing it from the fifo.
  * It returns 0 if the fifo was empty. Otherwise it returns the number
@@ -469,12 +464,10 @@ __kfifo_uint_must_check_helper( \
 __kfifo_uint_must_check_helper( \
 ({ \
         typeof((fifo) + 1) __tmp = (fifo); \
-        typeof((val) + 1) __val = (val); \
+        typeof(__tmp->ptr) __val = (val); \
         unsigned int __ret; \
         const size_t __recsize = sizeof(*__tmp->rectype); \
         struct __kfifo *__kfifo = &__tmp->kfifo; \
-        if (0) \
-                __val = (typeof(__tmp->ptr))NULL; \
         if (__recsize) \
                 __ret = __kfifo_out_peek_r(__kfifo, __val, sizeof(*__val), \
                         __recsize); \
@@ -508,14 +501,10 @@ __kfifo_uint_must_check_helper( \
 #define kfifo_in(fifo, buf, n) \
 ({ \
         typeof((fifo) + 1) __tmp = (fifo); \
-        typeof((buf) + 1) __buf = (buf); \
+        typeof(__tmp->ptr_const) __buf = (buf); \
         unsigned long __n = (n); \
         const size_t __recsize = sizeof(*__tmp->rectype); \
         struct __kfifo *__kfifo = &__tmp->kfifo; \
-        if (0) { \
-                typeof(__tmp->ptr_const) __dummy __attribute__ ((unused)); \
-                __dummy = (typeof(__buf))NULL; \
-        } \
         (__recsize) ?\
         __kfifo_in_r(__kfifo, __buf, __n, __recsize) : \
         __kfifo_in(__kfifo, __buf, __n); \
@@ -561,14 +550,10 @@ __kfifo_uint_must_check_helper( \
 __kfifo_uint_must_check_helper( \
 ({ \
         typeof((fifo) + 1) __tmp = (fifo); \
-        typeof((buf) + 1) __buf = (buf); \
+        typeof(__tmp->ptr) __buf = (buf); \
         unsigned long __n = (n); \
         const size_t __recsize = sizeof(*__tmp->rectype); \
         struct __kfifo *__kfifo = &__tmp->kfifo; \
-        if (0) { \
-                typeof(__tmp->ptr) __dummy = NULL; \
-                __buf = __dummy; \
-        } \
         (__recsize) ?\
         __kfifo_out_r(__kfifo, __buf, __n, __recsize) : \
         __kfifo_out(__kfifo, __buf, __n); \
@@ -773,14 +758,10 @@ __kfifo_uint_must_check_helper( \
 __kfifo_uint_must_check_helper( \
 ({ \
         typeof((fifo) + 1) __tmp = (fifo); \
-        typeof((buf) + 1) __buf = (buf); \
+        typeof(__tmp->ptr) __buf = (buf); \
         unsigned long __n = (n); \
         const size_t __recsize = sizeof(*__tmp->rectype); \
         struct __kfifo *__kfifo = &__tmp->kfifo; \
-        if (0) { \
-                typeof(__tmp->ptr) __dummy __attribute__ ((unused)) = NULL; \
-                __buf = __dummy; \
-        } \
         (__recsize) ? \
         __kfifo_out_peek_r(__kfifo, __buf, __n, __recsize) : \
         __kfifo_out_peek(__kfifo, __buf, __n); \