linux 驱动第4课 - 文件io

 

https://ke.qq.com/course/466167?taid=4166603608890615

1:  ls -al /dev 下面显示的第一个字母如果是c 代表的是字符设备，b 代表的是块设备

2: 后面的 信息里面，第一个是主设备好，第二个是次设备号

root@iZrj9e3565o1e423gw4xgiZ:~# ls -al /dev total 4 drwxr-xr-x 18 root root 3740 Jun 24 02:31 . drwxr-xr-x 25 root root 4096 Jun 24 02:53 .. crw-r--r-- 1 root root 10, 235 Jun 24 02:31 autofs drwxr-xr-x 2 root root 240 Jun 24 10:31 block crw------- 1 root root 10, 234 Jun 24 02:31 btrfs-control drwxr-xr-x 3 root root 60 Jun 24 02:30 bus drwxr-xr-x 2 root root 3240 Jun 24 02:31 char crw------- 1 root root 5, 1 Jun 24 02:31 console lrwxrwxrwx 1 root root 11 Jun 24 10:31 core -> /proc/kcore crw------- 1 root root 10, 60 Jun 24 02:31 cpu_dma_latency crw------- 1 root root 10, 203 Jun 24 02:31 cuse drwxr-xr-x 7 root root 140 Jun 24 10:31 disk drwxr-xr-x 3 root root 80 Jun 24 02:31 dri crw------- 1 root root 10, 62 Jun 24 02:31 ecryptfs crw-rw---- 1 root video 29, 0 Jun 24 02:31 fb0 lrwxrwxrwx 1 root root 13 Jun 24 10:31 fd -> /proc/self/fd crw-rw-rw- 1 root root 1, 7 Jun 24 02:31 full crw-rw-rw- 1 root root 10, 229 Jun 24 02:31 fuse crw------- 1 root root 244, 0 Jun 24 02:31 hidraw0 crw------- 1 root root 10, 228 Jun 24 02:31 hpet drwxr-xr-x 2 root root 0 Jun 24 02:31 hugepages crw------- 1 root root 10, 183 Jun 24 02:31 hwrng crw------- 1 root root 89, 0 Jun 24 02:31 i2c-0

3:  查用第二个

查看系统调用 使用man 2 open

Executable programs or shell commands // 命令 System calls (functions provided by the kernel) // 系统调用，比如 man 2 open Library calls (functions within program libraries) // 函数库调用 Special files (usually found in /dev) // 特殊文件, 比如 man 4 tty File formats and conventions eg /etc/passwd // 文件格式和约定, 比如man 5 passwd Games // 游戏 Miscellaneous (including macro packages and conventions), e.g. man(7), groff(7) //杂项 System administration commands (usually only for root) // 系统管理命令 Kernel routines [Non standard] // 内核例程 OPEN(2) Linux Programmer's Manual OPEN(2) NAME open, openat, creat - open and possibly create a file SYNOPSIS #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> int open(const char *pathname, int flags); int open(const char *pathname, int flags, mode_t mode); int creat(const char *pathname, mode_t mode); int openat(int dirfd, const char *pathname, int flags); int openat(int dirfd, const char *pathname, int flags, mode_t mode); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): openat(): Since glibc 2.10: _POSIX_C_SOURCE >= 200809L Before glibc 2.10: _ATFILE_SOURCE

4: 

有时间可以打一下 下面的代码：

#include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <unistd.h> #include <stdio.h> #include <sys/mman.h> /* * ./copy 1.txt 2.txt * argc = 3 * argv[0] = "./copy" * argv[1] = "1.txt" * argv[2] = "2.txt" */ int main(int argc, char **argv) { int fd_old, fd_new; struct stat stat; char *buf; /* 1. 判断参数 */ if (argc != 3) { printf("Usage: %s <old-file> <new-file>\n", argv[0]); return -1; } /* 2. 打开老文件 */ fd_old = open(argv[1], O_RDONLY); if (fd_old == -1) { printf("can not open file %s\n", argv[1]); return -1; } /* 3. 确定老文件的大小 */ if (fstat(fd_old, &stat) == -1) { printf("can not get stat of file %s\n", argv[1]); return -1; } /* 4. 映射老文件 */ buf = mmap(NULL, stat.st_size, PROT_READ, MAP_SHARED, fd_old, 0); if (buf == MAP_FAILED) { printf("can not mmap file %s\n", argv[1]); return -1; } /* 5. 创建新文件 */ fd_new = open(argv[2], O_WRONLY | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH); if (fd_new == -1) { printf("can not creat file %s\n", argv[2]); return -1; } /* 6. 写新文件 */ if (write(fd_new, buf, stat.st_size) != stat.st_size) { printf("can not write %s\n", argv[2]); return -1; } /* 5. 关闭文件 */ close(fd_old); close(fd_new); return 0; }