Double-fork() to avoid zombies
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23b62f621d
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@ -12,6 +12,7 @@
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#include <unistd.h>
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#include <sys/types.h>
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#include <signal.h>
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#include <sys/wait.h>
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#include <stdio.h>
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#include <fcntl.h>
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#include <string.h>
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@ -100,41 +101,67 @@ void child_sig_cb(struct ev_loop *loop, ev_child *watcher, int revents) {
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/*
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* Start a child-process with the specified command and reroute stdin.
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* We actually start a $SHELL to execute the command so we don't have to care
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* about arguments and such
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* about arguments and such.
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* We also double-fork() to avoid zombies and pass the pid of the child through a
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* temporary pipe back to i3bar
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*
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*/
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void start_child(char *command) {
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child_pid = 0;
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if (command != NULL) {
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int fd[2];
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int fd[2], tmp[2];
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/* This pipe will be used to communicate between e.g. i3status and i3bar */
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pipe(fd);
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child_pid = fork();
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switch (child_pid) {
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/* We also need this temporary pipe to get back the pid of i3status */
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pipe(tmp);
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switch (fork()) {
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case -1:
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ELOG("Couldn't fork()\n");
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exit(EXIT_FAILURE);
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case 0:
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/* Child-process. Reroute stdout and start shell */
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close(fd[0]);
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/* Double-fork(), so the child gets reparented to init */
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switch(child_pid = fork()) {
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case -1:
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ELOG("Couldn't fork() twice\n");
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exit(EXIT_FAILURE);
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case 0:
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/* Child-process. Reroute stdout and start shell */
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close(fd[0]);
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dup2(fd[1], STDOUT_FILENO);
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dup2(fd[1], STDOUT_FILENO);
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static const char *shell = NULL;
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static const char *shell = NULL;
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if ((shell = getenv("SHELL")) == NULL)
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shell = "/bin/sh";
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if ((shell = getenv("SHELL")) == NULL)
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shell = "/bin/sh";
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execl(shell, shell, "-c", command, (char*) NULL);
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return;
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execl(shell, shell, "-c", command, (char*) NULL);
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return;
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default:
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/* Temporary parent. We tell i3bar about the pid of i3status and exit */
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write(tmp[1], &child_pid, sizeof(int));
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close(tmp[0]);
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close(tmp[1]);
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exit(EXIT_SUCCESS);
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}
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default:
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/* Parent-process. Rerout stdin */
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close(fd[1]);
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dup2(fd[0], STDIN_FILENO);
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/* We also need to get the pid of i3status from the temporary pipe */
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size_t rec = 0;
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while (rec < sizeof(int)) {
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rec += read(tmp[0], &child_pid, sizeof(int) - rec);
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}
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/* The temporary pipe is no longer needed */
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close(tmp[0]);
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close(tmp[1]);
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break;
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}
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}
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wait(0);
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/* We set O_NONBLOCK because blocking is evil in event-driven software */
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fcntl(STDIN_FILENO, F_SETFL, O_NONBLOCK);
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