8.0 KiB
8.0 KiB
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）。
2. 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
对齐数据类型长度
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;