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linux 驱动程序 内核数据类型

## 内核的数据类型

 

### 基本数据类型

 

我们写了两个小的模块来测试实际数据类型和内存对齐的长度。

 

内核基本数据类型

 

 

 

C语言类型(int)

 

char、short、int、long long在不同的平台上大小不变。

 

long、ptr(指针)平台不同其大小不同,但二者的大小始终相同。

 

char的符号问题:

 

大多数平台上char默认是signed,但有些平台上默认是 unsigned。

char i = -1; 大部分平台上i是-1,有些平台上是255。

应该使用:signed char i = -1;   unsigned char i = 255;

确定大小的类型(u32)

 

u8、u16、u32、u64、 s8、s16、s32、s64是Linux内核确定大小的类型。

__u8等式linux用户态确定大小的类型。(头文件linux/types.h)

 

uint8_t、uint32_t是新编译器支持的C99标准确定大小的类型,可以跨平台。

特定内核对象的类型(pid_t)

 

进程标识符使用pid_t类型,而不使用int,屏蔽了实际的数据类型中任何可能的差异。

特定内核对象的类型,打印时,不太好选择printk或printf的输出格式:

 

  1.  一些平台上排除的警告,在另一平台上可能会出现(size_t在一些平台上是unsigned long,在一些平台上是unsigned int)。

 

  1. 将其强制转换成可能的最大类型,然后用响应的格式打印输出。

字节序

 

大端、小端

 

数值0x01020304,内存从低到高依次存储:04 03 02 01 为小端。 存储顺序反过来为大端)

 

数值0x00000001,内存从低到高依次存储:01 00 00 00 为小端。

 

转换函数

 

u32 __cpu_to_be32(u32);    /* 把cpu字节序转为大端字节序 */

 

u32 __be32_to_cpu(u32);    /* 把大端字节序转为cpu字节序 */

u32 __cpu_to_le32(u32);      /* 把cpu字节序转为小端字节序 */

u32 __le32_to_cpu(u32);      /* 把小端字节序转为cpu字节序 */

在头文件<linux/byteorder.h>中

 

 

时间间隔

 

使用HZ代表一秒。

 

不能假定每秒就1000个jiffies。

 

与msec毫秒对应的jiffies数目总是msec*HZ/1000。

 

页大小

 

页大小为PAGE_SIZE个字节,而不是4KB。

 

分配16KB的空间临时存储数据,如下:

 

 

以上,只是基本数据类型中最简单的一部分,绝大多数都是细节问题,要注意。

 

#### 基本数据类型的长度

图片5 图片6

 

#### 对齐数据类型长度

图片6

 

####  types.h 中的重要数据类型

 

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 unsigned short umode_t;

typedef __u32 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;

 

typedef _Bool bool;

 

typedef __kernel_uid32_t uid_t;

typedef __kernel_gid32_t gid_t;

typedef __kernel_uid16_t        uid16_t;

typedef __kernel_gid16_t        gid16_t;

 

typedef unsigned long uintptr_t;

 

#ifdef CONFIG_HAVE_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 */

 

#if defined(__GNUC__)

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__)

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 __u64 __attribute__((aligned(8)))

#define aligned_be64 __be64 __attribute__((aligned(8)))

#define aligned_le64 __le64 __attribute__((aligned(8)))

 

/**

* The type used for indexing onto a disc or disc partition.

*

* Linux always considers sectors to be 512 bytes long independently

* of the devices real block size.

*

* blkcnt_t is the type of the inode's block count.

*/

#ifdef CONFIG_LBDAF

typedef u64 sector_t;

typedef u64 blkcnt_t;

#else

typedef unsigned long sector_t;

typedef unsigned long blkcnt_t;

#endif

 

/*

* The type of an index into the pagecache.

*/

#define pgoff_t unsigned long

 

/*

* A dma_addr_t can hold any valid DMA address, i.e., any address returned

* by the DMA API.

*

* If the DMA API only uses 32-bit addresses, dma_addr_t need only be 32

* bits wide.  Bus addresses, e.g., PCI BARs, may be wider than 32 bits,

* but drivers do memory-mapped I/O to ioremapped kernel virtual addresses,

* so they don't care about the size of the actual bus addresses.

*/

#ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT

typedef u64 dma_addr_t;

#else

typedef u32 dma_addr_t;

#endif

 

typedef unsigned __bitwise__ gfp_t;

typedef unsigned __bitwise__ fmode_t;

typedef unsigned __bitwise__ oom_flags_t;

 

#ifdef CONFIG_PHYS_ADDR_T_64BIT

typedef u64 phys_addr_t;

#else

typedef u32 phys_addr_t;

#endif

 

typedef phys_addr_t resource_size_t;

 

/*

* This type is the placeholder for a hardware interrupt number. It has to be

* big enough to enclose whatever representation is used by a given platform.

*/

typedef unsigned long irq_hw_number_t;

 

typedef struct {

int counter;

} atomic_t;

 

#ifdef CONFIG_64BIT

typedef struct {

long counter;

} atomic64_t;

#endif

 

struct list_head {

struct list_head *next, *prev;

};

 

struct hlist_head {

struct hlist_node *first;

};

 

struct hlist_node {

struct hlist_node *next, **pprev;

};

 

struct ustat {

__kernel_daddr_t f_tfree;

__kernel_ino_t f_tinode;

char f_fname[6];

char f_fpack[6];

};

 

/**

* struct callback_head - callback structure for use with RCU and task_work

* @next: next update requests in a list

* @func: actual update function to call after the grace period.

*

* The struct is aligned to size of pointer. On most architectures it happens

* naturally due ABI requirements, but some architectures (like CRIS) have

* weird ABI and we need to ask it explicitly.

*

* The alignment is required to guarantee that bits 0 and 1 of @next will be

* clear under normal conditions -- as long as we use call_rcu(),

* call_rcu_bh(), call_rcu_sched(), or call_srcu() to queue callback.

*

* This guarantee is important for few reasons:

*  - future call_rcu_lazy() will make use of lower bits in the pointer;

*  - the structure shares storage spacer in struct page with @compound_head,

*    which encode PageTail() in bit 0. The guarantee is needed to avoid

*    false-positive PageTail().

*/

struct callback_head {

struct callback_head *next;

void (*func)(struct callback_head *head);

} __attribute__((aligned(sizeof(void *))));

#define rcu_head callback_head

 

typedef void (*rcu_callback_t)(struct rcu_head *head);

typedef void (*call_rcu_func_t)(struct rcu_head *head, rcu_callback_t func);

 

/* clocksource cycle base type */

typedef u64 cycle_t;

 

本文固定链接: http://zmrlinux.com/2017/05/10/linux-%e9%a9%b1%e5%8a%a8%e7%a8%8b%e5%ba%8f-%e5%86%85%e6%a0%b8%e6%95%b0%e6%8d%ae%e7%b1%bb%e5%9e%8b/ | Kernel & Me

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