对linux内核的数据类型做一下总结。
下面部分内容参考了：
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 |
下面是在其他平台上的数据类型所占的字节数：
|
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。所有类型在头文件中声明，这个文件又被头文件所包含。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
|
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，在中又把你所配置的体系结构中定义的类型的类型定义
包含进去了：下面把这个文件贴出来，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 */
|
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,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
|
现在，你看起内核的一些函数的参数的类型为loff_t，ssize_t这些类型就不会发怵了吧！呵呵。
不过我也发现了一个非常不错网站，你可以把linux 的一个参数或者数据类型输入进去，便可查询内部相关数据类型。
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