题
我已经准备了一个程序,该程序使用管道模拟Shell(CMD)接口。该程序有两个版本:1。使用一根管道(使用从父母到子传播的管道)2。使用双管(使用父母到子女的两个管道以及从子女到父母的两个管道进行交流)。
因此,第一个程序提供了所需的界面并起作用我想要的方式,但是我无法在第二个程序中达到相同的结果(接口)(使用DUP2()和相似)。
因此,我会在您的帮助下转达,并在下面放置两个代码。
BS:您可以使用以下命令以相同的方式进行编译并尝试这两个程序:
$ gcc prog1.c -o prog1
接下来让我们运行:
$ ./prog1
接下来,让我们运行新的终端,然后尝试将一些数据写入input.txt:
$ echo pwd> input.txt
然后在第一个终端观看结果。
(对于第一个程序的正常工作正常,但我需要在第二个程序中获得相同的界面的工作)
第一个程序的代码(正常工作):
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/stat.h>
void do_child(int data_pipe[]) {
int c;
int rc;
close(data_pipe[1]);
dup2(data_pipe[0], 0); /* This string provides the desired interface of the program */
char* cmd[] = { "bash", (char *)0 };
execvp("bash", cmd);
while ((rc = read(data_pipe[0], &c, 1)) > 0)
{
putchar(c);
}
exit(0);
}
void do_parent(int data_pipe[])
{
int c;
int rc;
FILE *in;
close(data_pipe[0]);
while (1)
{
in = fopen("input.txt", "r");
while ((c = fgetc(in)) > 0)
{
rc = write(data_pipe[1], &c, 1);
if (rc == -1)
{
perror("Parent: write");
close(data_pipe[1]);
exit(1);
}
}
fclose(in);
}
close(data_pipe[1]);
exit(0);
}
int main(int argc, char* argv[])
{
int data_pipe[2];
int pid;
int rc;
umask(0);
mknod("input.txt", S_IFIFO|0666, 0);
rc = pipe(data_pipe);
if (rc == -1)
{
perror("pipe");
exit(1);
}
pid = fork();
switch (pid)
{
case -1:
perror("fork");
exit(1);
case 0:
do_child(data_pipe);
default:
do_parent(data_pipe);
}
return 0;
}
第二个程序的代码(需要纠正一点):
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/stat.h>
/* Original version got from http://www.iakovlev.org */
int parent_to_child[2];
int child_to_parent[2];
void do_parent()
{
int c;
char ch;
int rc;
FILE *in;
close(child_to_parent[1]); /* we don't need to write to this pipe. */
close(parent_to_child[0]); /* we don't need to read from this pipe. */
while (1)
{
in = fopen("input.txt", "r");
while ((c = fgetc(in)) > 0) {
ch = (char)c;
/* write to child */
rc = write(parent_to_child[1], &ch, 1);
if (rc == -1) {
perror("child: write");
close(child_to_parent[0]);
close(parent_to_child[1]);
exit(1);
}
/* read back from child */
rc = read(child_to_parent[0], &ch, 1);
c = (int)ch;
if (rc <= 0) {
perror("parent: read");
close(child_to_parent[0]);
close(parent_to_child[1]);
exit(1);
}
putchar(c);
}
fclose(in);
}
close(child_to_parent[0]);
close(parent_to_child[1]);
exit(0);
}
void do_child()
{
int c;
char ch;
int rc;
close(parent_to_child[1]); /* we don't need to write to this pipe. */
close(child_to_parent[0]); /* we don't need to read from this pipe. */
//dup2(parent_to_child[0], STDIN_FILENO);
//dup2(child_to_parent[1], STDOUT_FILENO);
/* Some dup2() routines must be added here
to get this working as the first program above */
char* cmd[] = { "bash", (char *)0 };
execvp("bash", cmd);
while (read(parent_to_child[0], &ch, 1) > 0) {
c = (int)ch;
ch = (char)c;
putchar(ch);
rc = write(child_to_parent[1], &ch, 1);
if (rc == -1) {
perror("child: write");
close(parent_to_child[0]);
close(child_to_parent[1]);
exit(1);
}
}
close(parent_to_child[0]);
close(child_to_parent[1]);
exit(0);
}
int main(int argc, char* argv[])
{
int pid;
int rc;
umask(0);
mknod("input.txt", S_IFIFO|0666, 0);
rc = pipe(parent_to_child);
if (rc == -1) {
perror("main: pipe parent_to_child");
exit(1);
}
rc = pipe(child_to_parent);
if (rc == -1) {
perror("main: pipe child_to_parent");
exit(1);
}
pid = fork();
switch (pid) {
case -1:
perror("main: fork");
exit(1);
case 0:
do_child();
default:
do_parent();
}
return 0;
}
解决方案
主要区别在这里:
while ((c = fgetc(in)) > 0) {
ch = (char)c;
/* write to child */
rc = write(parent_to_child[1], &ch, 1);
/* .... */
/* read back from child */
rc = read(child_to_parent[0], &ch, 1);
/* .... */
putchar(c);
}
当我懒惰地为您编译/测试时,我只会推测父母在read()中被阻止。因为不能保证其他方面(在儿童过程中进行bash)回荡每个书面角色。否则它甚至可能决定打印多个字符,您的代码无法处理。
在情况下,您必须进行调查()查看是否需要阅读。或使用fcntl(f_setfl)在child_to_parent [0]上设置O_NONBLOCK标志,当Errno == Eagain时,只需跳过read()分支即可。和循环,而仍然有字符要读。
Edit1。 顺便说一句,我完全错过了这一部分:您在do_parent()循环中都必须在两者上使用poll() child_to_parent[0]
和 in
, ,由于另一侧可能会写东西(read()不会阻止),即使您不编写()任何字符。
其他提示
多亏了您,似乎我才能正常工作。
因此,这是do_parent的更新代码:
void do_parent()
{
int c;
char ch;
int rc;
FILE *in;
struct pollfd fds[2];
int pol_ret;
fds[0].fd = child_to_parent[0];
close(child_to_parent[1]); /* we don't need to write to this pipe. */
close(parent_to_child[0]); /* we don't need to read from this pipe. */
while (1)
{
in = fopen("input.txt", "r");
fds[1].fd = fileno(in);
pol_ret = poll(fds, 2, 500);
while ((c = fgetc(in)) > 0) {
ch = (char)c;
/* write to child */
rc = write(parent_to_child[1], &ch, 1);
if (rc == -1) {
perror("child: write");
close(child_to_parent[0]);
close(parent_to_child[1]);
exit(1);
}
/* read back from child */
if (fds[0].revents & POLLIN)
{
rc = read(child_to_parent[0], &ch, 1);
c = (int)ch;
if (rc <= 0) {
perror("parent: read");
close(child_to_parent[0]);
close(parent_to_child[1]);
exit(1);
}
putchar(c);
}
}
fclose(in);
}
close(child_to_parent[0]);
close(parent_to_child[1]);
exit(0);
}
我也将其添加到do_child():
dup2(parent_to_child[0], STDIN_FILENO);