01父子进程利用管道实现cp工具

思路:

创建管道，fork;然后在父进程中用fget从源文件中读取内容，然后写到管道；子进程从管道中读取内容，然后写入到目标文件

实现:

/***target : use fgets() and write() to copy files
 *  main points : pipe() fork()
 */
#include <sys/types.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/wait.h>

#define READBLOCK 1024

int main(int argc, char *argv[])
{
    FILE* sfp;
    int fd;
    char opt;
    int  wp[2];

    if(argc < 2){
        printf("Usage:\n    fcp [OPTION] SOURCE DEST\n");
        printf("OPTION: -r copy directories recursively\n");
        abort();
    }else if(argc == 3){
        sfp = fopen(argv[1], "r");
        fd = open(argv[2], O_CREAT | O_WRONLY | O_APPEND, 0666);
    }else if(argc == 4 && *argv[1] == 'r'){
        opt = *argv[1];
        sfp = fopen(argv[2], "r");
        fd = open(argv[2], O_CREAT | O_WRONLY | O_APPEND, 0666);
    }

    if(!sfp || (fd < 0))
    {
        printf("open error, errno: %d\n", errno);
        return 1;
    }

    pipe(wp);

    char buffer[READBLOCK];

    pid_t pid = fork();
    if(pid > 0)
    {
        close(wp[0]);
        FILE *wf = fdopen(wp[1], "w");
        size_t nread = 0, nwrite = 0;
        while(fgets(buffer, READBLOCK, sfp) != NULL)
        {
            nread = strlen(buffer);
            write(wp[1], buffer, nread);
        }

        close(wp[1]);

        if(waitpid(pid, NULL, 0) < 0)
            printf("waitpid error\n");

        fclose(sfp);
        close(fd);
        exit(0);
    }
    else if( pid == 0)
    {
        close(wp[1]);
        FILE* rf = fdopen(wp[0], "r");
        size_t nread = 0, nwrite = 0;
        while(fgets(buffer, READBLOCK, rf) != NULL)
        {
            nread = strlen(buffer);
            write(fd, buffer, nread);
            memset(buffer, '\0', READBLOCK);
        }
    }

}

---

理想是美好的，现实却是，利用父子进程通过管道实现cp工具就是一坨屎

，性能差得不行。

$ time cp file.0 tf1
real    0m6.077s
user    0m0.013s
sys    0m3.176s

$ time ./fcpv2 file.0 tf4
real	2m23.157s
user	0m17.228s
sys	2m38.983s