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Subject[PATCH] type safe allocator
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Date
From: Miklos Szeredi <mszeredi@suse.cz>

The linux kernel doesn't have a type safe object allocator a-la new()
in C++ or g_new() in glib.

Introduce two helpers for this purpose:

alloc_struct(type, gfp_flags);

zalloc_struct(type, gfp_flags);

These macros take a type name (usually a 'struct foo') as first
argument and the usual gfp-flags as second argument. They return a
pointer cast to 'type *'.

The traditional forms of allocating a structure are:

fooptr = kmalloc(sizeof(*fooptr), ...);

fooptr = kmalloc(sizeof(struct foo), ...);

The new form is preferred over these, because of it's type safety and
more descriptive nature.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---

Index: linux-2.6.22/include/linux/slab.h
===================================================================
--- linux-2.6.22.orig/include/linux/slab.h 2007-08-01 16:47:41.000000000 +0200
+++ linux-2.6.22/include/linux/slab.h 2007-08-02 12:55:20.000000000 +0200
@@ -110,6 +110,20 @@ static inline void *kcalloc(size_t n, si
return __kzalloc(n * size, flags);
}

+/**
+ * alloc_struct - allocate given type object
+ * @type: the type of the object to allocate
+ * @flags: the type of memory to allocate.
+ */
+#define alloc_struct(type, flags) ((type *) kmalloc(sizeof(type), flags))
+
+/**
+ * zalloc_struct - allocate given type object, zero out the contents
+ * @type: the type of the object to allocate
+ * @flags: the type of memory to allocate.
+ */
+#define zalloc_struct(type, flags) ((type *) kzalloc(sizeof(type), flags))
+
/*
* Allocator specific definitions. These are mainly used to establish optimized
* ways to convert kmalloc() calls to kmem_cache_alloc() invocations by selecting
Index: linux-2.6.22/Documentation/CodingStyle
===================================================================
--- linux-2.6.22.orig/Documentation/CodingStyle 2007-07-09 01:32:17.000000000 +0200
+++ linux-2.6.22/Documentation/CodingStyle 2007-08-02 13:03:48.000000000 +0200
@@ -631,21 +631,20 @@ Printing numbers in parentheses (%d) add
Chapter 14: Allocating memory

The kernel provides the following general purpose memory allocators:
-kmalloc(), kzalloc(), kcalloc(), and vmalloc(). Please refer to the API
+kmalloc(), kzalloc(), kcalloc(), and vmalloc(), and the following
+helpers: alloc_struct() and zalloc_struct(). Please refer to the API
documentation for further information about them.

-The preferred form for passing a size of a struct is the following:
+The preferred form for allocating a structure is the following:

- p = kmalloc(sizeof(*p), ...);
+ p = alloc_struct(struct name, ...);

-The alternative form where struct name is spelled out hurts readability and
-introduces an opportunity for a bug when the pointer variable type is changed
-but the corresponding sizeof that is passed to a memory allocator is not.
-
-Casting the return value which is a void pointer is redundant. The conversion
-from void pointer to any other pointer type is guaranteed by the C programming
-language.
+The alternatives are less readable or introduce an opportunity for a bug
+when the pointer variable type is changed but the corresponding sizeof that
+is passed to a memory allocator is not.

+The return value of alloc_struct() and zalloc_struct() have the right type,
+so the compiler will warn if it is assigned to a pointer of different type.

Chapter 15: The inline disease

-
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