begin simple child process interface

cli/child.c

@@ -0,0 +1,63 @@
+#include <signal.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <sys/wait.h>
+
+#include "child.h"
+#include "epty.h"
+
+/* SIGTERM grace period before a child is sent SIGKILL.
+ * Value is in microseconds (us), 1000us = 1ms */
+#define CHILD_GRACE_US 100000
+
+/* Check if a child is still alive by pid
+ * by kill(3p) sending a null signal (0).
+ */
+static int is_alive(struct d_child *child) {
+  return (kill(child->pid, 0) == 0);
+}
+
+/* Force a child to die, first by sending SIGTERM, otherwise SIGKILL.
+ * NOTE: killchild() ASSUMES the child is LIVING at the start.
+ * NOTE: Keep this in mind when threading!
+ */
+void killchild(struct d_child *child) {
+  int stat;
+
+  /* Request Death */
+  kill(child->pid, SIGTERM);
+  usleep(CHILD_GRACE_US);
+  
+  /* Force Death */
+  if (is_alive(child))  
+    kill(child->pid, SIGKILL);
+
+  /* Reap */
+  waitpid(child->pid, &stat, 0);
+}
+
+/* Fork to spawn a child process running bin/shfx in an "epty".
+ */
+int spawnchild(struct d_child *child) {
+  *child = (struct d_child){ 0 };
+  
+  /* fork(2) and allocate an "error-piped pseudoterminal" (epty) */
+  switch (child->pid = forkepty(&child->fdmx, &child->fderr)) {
+  case -1:
+    perror("forkepty");
+    return EXIT_FAILURE;
+  case 0:
+    char *args[] = {"shfx", NULL};
+    execvp("shfx", args);
+    perror("execvp");
+    exit(1);
+  default:
+    usleep(1000);
+    char bufout[10];
+    bufout[9] = '\0';
+    read(child->fdmx, bufout, 9);
+    printf("child stdout: \"%s\"\n", bufout);
+    break;
+  }
+  return EXIT_SUCCESS;
+}

cli/child.h

@@ -0,0 +1,14 @@
+#ifndef DORNE_CHILD_H
+#define DORNE_CHILD_H
+
+#include <unistd.h>
+
+struct d_child {
+  pid_t pid;
+  int fdmx; /* PTY master fd (read/write) */
+  int fderr; /* child's stderr (readonly) */
+} __attribute__((packed, aligned(4)));
+
+int spawnchild(struct d_child *child);
+
+#endif /* DORNE_CHILD_H */

cli/main.c

@@ -1,7 +1,8 @@
-#include <stdio.h>
+#include <fcntl.h>
 #include <stdlib.h>
+#include <unistd.h>
 
-#include "mkpty.h"
+#include "child.h"
 
 // struct d_window {
 //   int ptmx; // fd
@@ -14,17 +15,7 @@
 // }
 
 int main(int argc, char **argv) {
-  pid_t pid;
-  switch (pid = forkmkpty()) {
-  case -1:
-    perror("forkmkpty");
-    break;
-  case 0:
-    printf("fork: children\n");
-    break;
-  default:
-    printf("fork: parent\n");
-    break;
-  }
+  struct d_child child;
+  spawnchild(&child);
   return EXIT_SUCCESS;
 }