## 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 ![df](./image/ssd.png) #### 对齐数据类型长度 ![fs](./image/dfd.png) #### 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; ``` #### list.h