114 lines
3.0 KiB
C
114 lines
3.0 KiB
C
/*
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* popen.c Written by W. Richard Stevens
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* write 20180623 email: aixiao@aixiao.me
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*/
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#include <stdio.h>
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#include <unistd.h>
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#include <stdlib.h>
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#include <sys/wait.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <sys/resource.h>
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static pid_t *childpid = NULL;
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/* ptr to array allocated at run-time */
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static int maxfd; /* from our open_max(), {Prog openmax} */
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#define SHELL "/bin/sh"
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FILE *_popen(const char *cmdstring, const char *type)
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{
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int i, pfd[2];
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pid_t pid;
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FILE *fp;
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/* only allow "r" or "w" */
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if ((type[0] != 'r' && type[0] != 'w') || type[1] != 0) {
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errno = EINVAL; /* required by POSIX.2 */
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return (NULL);
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}
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if (childpid == NULL) { /* first time through */
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/* allocate zeroed out array for child pids */
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#if 0
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maxfd = open_max();
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#else
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/* OPEN_MAX is canceled after linux-2.6.24, and become a part of RLIMIT_NOFILE.
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Execute shell 'ulimit -a' to get more information */
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struct rlimit limit;
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if (getrlimit(RLIMIT_NOFILE, &limit) == -1) {
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perror("getrlimit fail");
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return (NULL);
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}
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maxfd = limit.rlim_cur;
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//print("rlimit = %d.\n", maxfd);
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#endif
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if ((childpid = calloc(maxfd, sizeof(pid_t))) == NULL)
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return (NULL);
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}
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if (pipe(pfd) < 0)
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return (NULL); /* errno set by pipe() */
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if ((pid = fork()) < 0)
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return (NULL); /* errno set by fork() */
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else if (pid == 0) { /* child */
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if (*type == 'r') {
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close(pfd[0]);
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if (pfd[1] != STDOUT_FILENO) {
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dup2(pfd[1], STDOUT_FILENO);
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close(pfd[1]);
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}
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} else {
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close(pfd[1]);
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if (pfd[0] != STDIN_FILENO) {
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dup2(pfd[0], STDIN_FILENO);
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close(pfd[0]);
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}
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}
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/* close all descriptors in childpid[] */
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for (i = 0; i < maxfd; i++)
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if (childpid[i] > 0)
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close(i);
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execl(SHELL, "sh", "-c", cmdstring, (char *)0);
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exit(127);
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}
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/* parent */
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if (*type == 'r') {
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close(pfd[1]);
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if ((fp = fdopen(pfd[0], type)) == NULL)
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return (NULL);
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} else {
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close(pfd[0]);
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if ((fp = fdopen(pfd[1], type)) == NULL)
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return (NULL);
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}
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childpid[fileno(fp)] = pid; /* remember child pid for this fd */
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return (fp);
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}
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int _pclose(FILE * fp)
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{
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int fd, stat;
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pid_t pid;
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if (childpid == NULL)
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return (-1); /* popen() has never been called */
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fd = fileno(fp);
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if ((pid = childpid[fd]) == 0)
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return (-1); /* fp wasn't opened by popen() */
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childpid[fd] = 0;
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if (fclose(fp) == EOF)
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return (-1);
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while (waitpid(pid, &stat, 0) < 0)
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if (errno != EINTR)
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return (-1); /* error other than EINTR from waitpid() */
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return (stat); /* return child's termination status */
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}
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