linux常用資料類型

 

當Linux核心在體繫結構差異較大的平台之間移植時，會產生與資料類型相關的問題。在編譯核心時使用 -Wall -Wstrict-prototypes選項，可以避免很多錯誤的發生。

核心使用的基礎資料型別 (Elementary Data Type)主要有：

ØØ int          標準C語言整數類型；

ØØ u32          32位整數類型；

ØØ pid_t        特定核心對象pid的類型。

在不同的CPU體繫結構上，C語言的資料類型所佔空間不一樣。下面是在x86下資料類型所佔的位元組數：

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資料類型所佔的位元組數：

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

其中基於sparc64平台的Linux使用者空間可以運行32位代碼，使用者空間指標是32位寬的，但核心空間是64位的。

核心中的地址是unsigned long類型，指標大小和long類型相同。

核心提供下列資料類型。所有類型在標頭檔<include/asm/types.h>中聲明，這個檔案又被標頭檔<Linux/types.h>所包含。下面是include/asm/types.h檔案。這是對ARM體繫結構中 /asm/types.h檔案中的一些定義： 因為我是對arm體繫結構進行了配置

#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

 

使用有首碼的類型用於將變數顯露給使用者空間，如_ _u8類型。例如：一個驅動程式通過ioctl函數與運行在使用者空間的程式交換資料，應該用_ _u32來聲明32位的資料類型。

有時核心使用C語言的類型，如unsigned int，這通常用於大小獨立於體繫結構的資料項目。 核心中許多資料類型由typedef聲明，這樣方便移植。如使用pid_t類型作為進程標誌符（pid）的類型，而不是int類型，pid_t屏蔽了在不同平台上的實際資料類型的差異。

如果不容易選擇合適的類型，就將其強制轉換成最可能的類型（long或unsigned long）。

如上面所說，在<include/linux/types.h>中又把你所配置的體繫結構中定義的類型的類型定義

<include/asm/types.h>包含進去了：下面把<include/linux/types.h>這個檔案貼出來，我的核心版本是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 */

 

這裡面我以可以看到一些自訂類型，如loff_t,size_t等。

typedef __kernel_uid_t        uid_t;
typedef __kernel_gid_t        gid_t;

typedef __kernel_loff_t        loff_t;

這樣就將loff_t類型定義為__kernel_loff_t這個類型了,uid_t類型定義了__kernel_uid_t類型了，但是現在__kernel_loff_t __kernel_uid_t這種類型是很明顯地與體繫結構是相關的，對於arm的體繫結構，則定義在<include/asm-arm/posix_types.h>,代碼如下：

 

/*  * 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

 

現在，你看起核心的一些函數的參數的類型為loff_t，ssize_t這些類型就不會發怵了吧！呵呵。

不過我也發現了一個非常不錯網站，你可以把linux 的一個參數或者資料類型輸入進去，便可查詢內部相關資料類型。

http://www.gelato.unsw.edu.au/lxr/ident?i=loff_t