From 1ea2764a30cd2fbad93a1a6d8b13ce1e5fdb8f8c Mon Sep 17 00:00:00 2001
From: uxtbd <dev@kthread.dev>
Date: Tue, 18 Aug 2026 09:40:18 -0300
Subject: 4init: minimal but functional init

---
 4init/4init.c | 82 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 82 insertions(+)
 create mode 100644 4init/4init.c

(limited to '4init/4init.c')

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;
+				}
+			}
+		}
+	}
+}
-- 
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