对linux内核的数据类型做一下总结。
下面部分内容参考了：http://book.csdn.net/bookfiles/12/100126.shtml
当Linux内核在体系结构差异较大的平台之间移植时，会产生与数据类型相关的问题。在编译内核时使用 -Wall -Wstrict-prototypes选项，可以避免很多错误的发生。
内核使用的基本数据类型主要有：
ØØ int 标准C语言整数类型；
ØØ u32 32位整数类型；
ØØ pid_t 特定内核对象pid的类型。
在不同的CPU体系结构上，C语言的数据类型所占空间不一样。下面是在x86下数据类型所占的字节数：
arch
| char
| short
| int
| long
| ptr
| long-long
| u8
| u16
| u32
| u64
| i686
| 1
| 2
| 4
| 4
| 4
| 8
| 1
| 2
| 4
| 8
|
arch
| char
| short
| int
| long
| ptr
| long-long
| u8
| u16
| u32
| u64
| i386
| 1
| 2
| 4
| 4
| 4
| 8
| 1
| 2
| 4
| 8
| alpha
| 1
| 2
| 4
| 8
| 8
| 8
| 1
| 2
| 4
| 8
| armv4l
| 1
| 2
| 4
| 4
| 4
| 8
| 1
| 2
| 4
| 8
| ia64
| 1
| 2
| 4
| 8
| 8
| 8
| 1
| 2
| 4
| 8
| m68k
| 1
| 2
| 4
| 4
| 4
| 8
| 1
| 2
| 4
| 8
| mips
| 1
| 2
| 4
| 4
| 4
| 8
| 1
| 2
| 4
| 8
| ppc
| 1
| 2
| 4
| 4
| 4
| 8
| 1
| 2
| 4
| 8
| sparc
| 1
| 2
| 4
| 4
| 4
| 8
| 1
| 2
| 4
| 8
| sparc64
| 1
| 2
| 4
| 4
| 4
| 8
| 1
| 2
| 4
| 8
|
其中基于sparc64平台的Linux用户空间可以运行32位代码，用户空间指针是32位宽的，但内核空间是64位的。
内核中的地址是unsigned long类型，指针大小和long类型相同。
内核提供下列数据类型。所有类型在头文件<include/asm/types.h>中声明，这个文件又被头文件<Linux/types.h>所包含。下面是include/asm/types.h文件。这是对ARM体系结构中 /asm/types.h文件中的一些定义： 因为我是对arm体系结构进行了配置
#ifndef __ASM_ARM_TYPES_H
#define __ASM_ARM_TYPES_H
#ifndef __ASSEMBLY__
typedef unsigned short umode_t;
/*
* __xx is ok: it doesn't pollute the POSIX namespace. Use these in the
* header files exported to user space
*/
typedef __signed__ char __s8;
typedef unsigned char __u8;
typedef __signed__ short __s16;
typedef unsigned short __u16;
typedef __signed__ int __s32;
typedef unsigned int __u32;
#if defined(__GNUC__) && !defined(__STRICT_ANSI__)
typedef __signed__ long long __s64;
typedef unsigned long long __u64;
#endif
#endif /* __ASSEMBLY__ */
/*
* These aren't exported outside the kernel to avoid name space clashes
*/
#ifdef __KERNEL__
#define BITS_PER_LONG 32
#ifndef __ASSEMBLY__
typedef signed char s8;
typedef unsigned char u8;
typedef signed short s16;
typedef unsigned short u16;
typedef signed int s32;
typedef unsigned int u32;
typedef signed long long s64;
typedef unsigned long long u64;
/* Dma addresses are 32-bits wide. */
typedef u32 dma_addr_t;
typedef u32 dma64_addr_t;
#endif /* __ASSEMBLY__ */
#endif /* __KERNEL__ */
#endif
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使用有前缀的类型用于将变量显露给用户空间，如_ _u8类型。例如：一个驱动程序通过ioctl函数与运行在用户空间的程序交换数据，应该用_ _u32来声明32位的数据类型。
有时内核使用C语言的类型，如unsigned int，这通常用于大小独立于体系结构的数据项。 内核中许多数据类型由typedef声明，这样方便移植。如使用pid_t类型作为进程标志符（pid）的类型，而不是int类型，pid_t屏蔽了在不同平台上的实际数据类型的差异。
如果不容易选择合适的类型，就将其强制转换成最可能的类型（long或unsigned long）。
如上面所说，在<include/linux/types.h>中又把你所配置的体系结构中定义的类型的类型定义
<include/asm/types.h>包含进去了：下面把<include/linux/types.h>这个文件贴出来，我的内核版本是2.6.16.28。
#ifndef _LINUX_TYPES_H
#define _LINUX_TYPES_H
#ifdef __KERNEL__
#include <linux/config.h>
#define BITS_TO_LONGS(bits) /
(((bits)+BITS_PER_LONG-1)/BITS_PER_LONG)
#define DECLARE_BITMAP(name,bits) /
unsigned long name[BITS_TO_LONGS(bits)]
#define BITS_PER_BYTE 8
#endif
#include <linux/posix_types.h>
#include <asm/types.h>
#ifndef __KERNEL_STRICT_NAMES
typedef __u32 __kernel_dev_t;
typedef __kernel_fd_set fd_set;
typedef __kernel_dev_t dev_t;
typedef __kernel_ino_t ino_t;
typedef __kernel_mode_t mode_t;
typedef __kernel_nlink_t nlink_t;
typedef __kernel_off_t off_t;
typedef __kernel_pid_t pid_t;
typedef __kernel_daddr_t daddr_t;
typedef __kernel_key_t key_t;
typedef __kernel_suseconds_t suseconds_t;
typedef __kernel_timer_t timer_t;
typedef __kernel_clockid_t clockid_t;
typedef __kernel_mqd_t mqd_t;
#ifdef __KERNEL__
typedef __kernel_uid32_t uid_t;
typedef __kernel_gid32_t gid_t;
typedef __kernel_uid16_t uid16_t;
typedef __kernel_gid16_t gid16_t;
#ifdef CONFIG_UID16
/* This is defined by include/asm-{arch}/posix_types.h */
typedef __kernel_old_uid_t old_uid_t;
typedef __kernel_old_gid_t old_gid_t;
#endif /* CONFIG_UID16 */
/* libc5 includes this file to define uid_t, thus uid_t can never change
* when it is included by non-kernel code
*/
#else
typedef __kernel_uid_t uid_t;
typedef __kernel_gid_t gid_t;
#endif /* __KERNEL__ */
#if defined(__GNUC__) && !defined(__STRICT_ANSI__)
typedef __kernel_loff_t loff_t;
#endif
/*
* The following typedefs are also protected by individual ifdefs for
* historical reasons:
*/
#ifndef _SIZE_T
#define _SIZE_T
typedef __kernel_size_t size_t;
#endif
#ifndef _SSIZE_T
#define _SSIZE_T
typedef __kernel_ssize_t ssize_t;
#endif
#ifndef _PTRDIFF_T
#define _PTRDIFF_T
typedef __kernel_ptrdiff_t ptrdiff_t;
#endif
#ifndef _TIME_T
#define _TIME_T
typedef __kernel_time_t time_t;
#endif
#ifndef _CLOCK_T
#define _CLOCK_T
typedef __kernel_clock_t clock_t;
#endif
#ifndef _CADDR_T
#define _CADDR_T
typedef __kernel_caddr_t caddr_t;
#endif
/* bsd */
typedef unsigned char u_char;
typedef unsigned short u_short;
typedef unsigned int u_int;
typedef unsigned long u_long;
/* sysv */
typedef unsigned char unchar;
typedef unsigned short ushort;
typedef unsigned int uint;
typedef unsigned long ulong;
#ifndef __BIT_TYPES_DEFINED__
#define __BIT_TYPES_DEFINED__
typedef __u8 u_int8_t;
typedef __s8 int8_t;
typedef __u16 u_int16_t;
typedef __s16 int16_t;
typedef __u32 u_int32_t;
typedef __s32 int32_t;
#endif /* !(__BIT_TYPES_DEFINED__) */
typedef __u8 uint8_t;
typedef __u16 uint16_t;
typedef __u32 uint32_t;
#if defined(__GNUC__) && !defined(__STRICT_ANSI__)
typedef __u64 uint64_t;
typedef __u64 u_int64_t;
typedef __s64 int64_t;
#endif
/* this is a special 64bit data type that is 8-byte aligned */
#define aligned_u64 unsigned long long __attribute__((aligned(8)))
/*
* The type used for indexing onto a disc or disc partition.
* If required, asm/types.h can override it and define
* HAVE_SECTOR_T
*/
#ifndef HAVE_SECTOR_T
typedef unsigned long sector_t;
#endif
/*
* The type of an index into the pagecache. Use a #define so asm/types.h
* can override it.
*/
#ifndef pgoff_t
#define pgoff_t unsigned long
#endif
#endif /* __KERNEL_STRICT_NAMES */
/*
* Below are truly Linux-specific types that should never collide with
* any application/library that wants linux/types.h.
*/
#ifdef __CHECKER__
#define __bitwise__ __attribute__((bitwise))
#else
#define __bitwise__
#endif
#ifdef __CHECK_ENDIAN__
#define __bitwise __bitwise__
#else
#define __bitwise
#endif
typedef __u16 __bitwise __le16;
typedef __u16 __bitwise __be16;
typedef __u32 __bitwise __le32;
typedef __u32 __bitwise __be32;
#if defined(__GNUC__) && !defined(__STRICT_ANSI__)
typedef __u64 __bitwise __le64;
typedef __u64 __bitwise __be64;
#endif
#ifdef __KERNEL__
typedef unsigned __bitwise__ gfp_t;
#endif
struct ustat {
__kernel_daddr_t f_tfree;
__kernel_ino_t f_tinode;
char f_fname[6];
char f_fpack[6];
};
#endif /* _LINUX_TYPES_H */
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这里面我以可以看到一些自定义类型，如loff_t,size_t等。
typedef __kernel_uid_t uid_t;
typedef __kernel_gid_t gid_t;
typedef __kernel_loff_t loff_t;
这样就将loff_t类型定义为__kernel_loff_t这个类型了,uid_t类型定义了__kernel_uid_t类型了，但是现在__kernel_loff_t __kernel_uid_t这种类型是很明显地与体系结构是相关的，对于arm的体系结构，则定义在<include/asm-arm/posix_types.h>,代码如下：
/*
* linux/include/asm-arm/posix_types.h
*
* Copyright (C) 1996-1998 Russell King.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* Changelog:
* 27-06-1996 RMK Created
*/
#ifndef __ARCH_ARM_POSIX_TYPES_H
#define __ARCH_ARM_POSIX_TYPES_H
/*
* This file is generally used by user-level software, so you need to
* be a little careful about namespace pollution etc. Also, we cannot
* assume GCC is being used.
*/
typedef unsigned long __kernel_ino_t;
typedef unsigned short __kernel_mode_t;
typedef unsigned short __kernel_nlink_t;
typedef long __kernel_off_t;
typedef int __kernel_pid_t;
typedef unsigned short __kernel_ipc_pid_t;
typedef unsigned short __kernel_uid_t;
typedef unsigned short __kernel_gid_t;
typedef unsigned int __kernel_size_t;
typedef int __kernel_ssize_t;
typedef int __kernel_ptrdiff_t;
typedef long __kernel_time_t;
typedef long __kernel_suseconds_t;
typedef long __kernel_clock_t;
typedef int __kernel_timer_t;
typedef int __kernel_clockid_t;
typedef int __kernel_daddr_t;
typedef char * __kernel_caddr_t;
typedef unsigned short __kernel_uid16_t;
typedef unsigned short __kernel_gid16_t;
typedef unsigned int __kernel_uid32_t;
typedef unsigned int __kernel_gid32_t;
typedef unsigned short __kernel_old_uid_t;
typedef unsigned short __kernel_old_gid_t;
typedef unsigned short __kernel_old_dev_t;
#ifdef __GNUC__
typedef long long __kernel_loff_t;
#endif
typedef struct {
#if defined(__KERNEL__) || defined(__USE_ALL)
int val[2];
#else /* !defined(__KERNEL__) && !defined(__USE_ALL) */
int __val[2];
#endif /* !defined(__KERNEL__) && !defined(__USE_ALL) */
} __kernel_fsid_t;
#if defined(__KERNEL__) || !defined(__GLIBC__) || (__GLIBC__ < 2)
#undef __FD_SET
#define __FD_SET(fd, fdsetp) /
(((fd_set *)(fdsetp))->fds_bits[(fd) >> 5] |= (1<<((fd) & 31)))
#undef __FD_CLR
#define __FD_CLR(fd, fdsetp) /
(((fd_set *)(fdsetp))->fds_bits[(fd) >> 5] &= ~(1<<((fd) & 31)))
#undef __FD_ISSET
#define __FD_ISSET(fd, fdsetp) /
((((fd_set *)(fdsetp))->fds_bits[(fd) >> 5] & (1<<((fd) & 31))) != 0)
#undef __FD_ZERO
#define __FD_ZERO(fdsetp) /
(memset (fdsetp, 0, sizeof (*(fd_set *)(fdsetp))))
#endif
#endif
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