4init: minimal but functional init

1 files changed, 82 insertions, 0 deletions

diff --git a/4init/4init.c b/4init/4init.c
new file mode 100644
index 0000000..50807b6
--- /dev/null
+++ b/4init/4init.c
@@ -0,0 +1,82 @@
+#define _POSIX_C_SOURCE 200809L
+
+#include <signal.h>
+#include <stdio.h>
+#include <sys/signalfd.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "config.h"
+
+static void reap(void)
+{
+        int status;
+        while (waitpid(-1, &status, WNOHANG) > 0) {}
+}
+
+int main(void)
+{
+        int sigfd = -1;
+        pid_t pid = -1;
+        sigset_t set;
+
+        if (getpid() != 1) {
+                fprintf(stderr, "4init - you need to run this as PID 1...\n");
+                return 1;
+        }
+
+        sigfillset(&set);
+        sigdelset(&set, SIGILL);
+        sigdelset(&set, SIGTRAP);
+        sigdelset(&set, SIGBUS);
+        sigdelset(&set, SIGFPE);
+        sigdelset(&set, SIGSEGV);
+
+        if (sigprocmask(SIG_SETMASK, &set, NULL) < 0) {
+                perror("sigprocmask");
+                return 1;
+        }
+
+        sigfd = signalfd(-1, &set, SFD_CLOEXEC);
+        if (sigfd < 0) {
+                perror("signalfd");
+                return 1;
+        }
+
+        pid = fork();
+        if (pid < 0) {
+                perror("fork");
+                return 1;
+        }
+
+        if (pid == 0) {
+                sigset_t empty_set;
+
+                sigemptyset(&empty_set);
+                sigprocmask(SIG_SETMASK, &empty_set, NULL);
+
+                if (setsid() == -1) {
+                        perror("setsid");
+                }
+
+                close(sigfd);
+
+                execve(rc_path, rc_argv, rc_envp);
+                perror("execve");
+                _exit(1);
+        } else {
+                struct signalfd_siginfo fdsi;
+
+                reap();
+
+                for (;;) {
+                        if (read(sigfd, &fdsi, sizeof(fdsi)) == sizeof(fdsi)) {
+                                switch (fdsi.ssi_signo) {
+                                case SIGCHLD:
+                                        reap();
+                                        break;
+                                }
+                        }
+                }
+        }
+}