Linux 进程间通信 -- mmap实现多进程cp文件

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

/// argv[1]: process num
/// argv[2]: file path
int main(int argc, char *argv[]) {
  if (argc < 3) {
    printf("bad argv, need 3 arg\n");
    return -1;
  }
  // filesize
  struct stat sbuf;
  int ret = stat(argv[2], &sbuf);
  if (ret < 0) {
    perror("stat");
    return -1;
  }

  // filesize
  off_t sz = sbuf.st_size;
  off_t yu = sz % atoi(argv[1]);
  // ever process
  off_t proSz = (sz - yu) / atoi(argv[1]);
  // open source file
  int srcfd = open(argv[2], O_RDONLY);
  // create target file
  char wk[20] = {0};
  sprintf(wk, "%s.copy", argv[2]);
  int decfd = open(wk, O_RDWR | O_CREAT | O_TRUNC, 0766);
  // change size
  ret = ftruncate(decfd, sz);
  if (ret < 0) {
    perror("ftruncate");
    return -1;
  }

  void *src = mmap(NULL, sz, PROT_READ, MAP_SHARED, srcfd, 0);
  if (src == MAP_FAILED) {
    perror("mmap src:");
    return -1;
  }

  // des mmap
  void *dst = mmap(NULL, sz, PROT_WRITE | PROT_READ, MAP_SHARED, decfd, 0);
  if (dst == MAP_FAILED) {
    perror("mmap dst:");
    return -1;
  }

  int i;
  int pCnt = atoi(argv[i]);

  // create child pid
  for (i = 0; i < pCnt; ++i) {
    // in child process
    if (fork() == 0)
      break;
  }
  // in child process
  //子进程的处理
  if (i < pCnt) {
    // last time
    if (i == pCnt - 1) {
      memcpy(dst + i * proSz, src + i * proSz, proSz + yu);
    } else {
      memcpy(dst + i * proSz, src + i * proSz, proSz);
    }
  }
  //父进程的处理
  else {
    /// wait child pid
    for (int i = 0; i < pCnt; ++i) {
      wait(NULL);
    }
    // printf("parent pid=%d\n", getpid());
    if (munmap(src, sz) == -1) {
      perror("munmap src");
    }
    if (munmap(dst, sz) == -1) {
      perror("munmap dsc");
    }
    close(srcfd);
    close(decfd);
  }
  return 0;
}