First draft

Signed-off-by: Adrien Gallouët <[email protected]>

.gitignore

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+init

LICENSE

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+Copyright (c) 2015-2020, Adrien Gallouët <[email protected]>
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+* Redistributions of source code must retain the above copyright notice, this
+  list of conditions and the following disclaimer.
+
+* Redistributions in binary form must reproduce the above copyright notice,
+  this list of conditions and the following disclaimer in the documentation
+  and/or other materials provided with the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+

Makefile

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+DESTDIR ?=
+
+.PHONY: all
+all: init
+
+.PHONY: install
+install: init
+	install -s init $(DESTDIR)/
+
+.PHONY: clean
+clean:
+	rm -f init

init.c

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+#define _GNU_SOURCE
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include <sys/stat.h>
+#include <sys/wait.h>
+#include <sys/mount.h>
+
+static void
+spawn(const char *cmd)
+{
+    pid_t pid = fork();
+
+    if (pid == (pid_t)-1) {
+        perror("fork");
+        return;
+    }
+
+    if (pid == (pid_t)0) {
+        static sigset_t set;
+        sigfillset(&set);
+        sigprocmask(SIG_UNBLOCK, &set, NULL);
+        setsid();
+        execl(cmd, cmd, (char *)NULL);
+        perror("execl");
+        _exit(1);
+    }
+
+    while (waitpid(-1, NULL, 0) != pid);
+}
+
+static void
+init_fs(void)
+{
+    chdir("/");
+
+    if (mount(NULL, "/", NULL, MS_NOSUID|MS_REMOUNT, NULL))
+        perror("remount(/)");
+
+    mkdir("/dev", 0755);
+    mkdir("/proc", 0755);
+    mkdir("/tmp", 01777);
+    mkdir("/sys", 0755);
+
+    if (mount("none", "/dev", "devtmpfs", 0, NULL))
+        perror("mount(dev)");
+
+    if (mount("none", "/proc", "proc", 0, NULL))
+        perror("mount(proc)");
+
+    if (mount("none", "/sys", "sysfs", 0, NULL))
+        perror("mount(sys)");
+
+    if (mount("none", "/sys/fs/cgroup", "cgroup2", 0, NULL))
+        perror("mount(cgroup2)");
+
+    mkdir("/dev/pts", 0755);
+    mkdir("/dev/shm", 0755);
+
+    if (mount("devpts", "/dev/pts", "devpts", 0, "gid=5,mode=0620,ptmxmode=0666"))
+        perror("mount(devpts)");
+}
+
+static void
+init_console(void)
+{
+    int fd = open("/dev/console", O_RDWR | O_NONBLOCK | O_NOCTTY);
+
+    if (fd < 0) {
+        perror("open(console)");
+        return;
+    }
+
+    dup2(fd, 0);
+    dup2(fd, 1);
+    dup2(fd, 2);
+
+    if (fd > 2)
+        close(fd);
+}
+
+static void
+init_term(void)
+{
+    if (getenv("TERM"))
+        return;
+
+    putenv("TERM=linux");
+}
+
+int
+main(void)
+{
+    if (getpid() != 1)
+        return 1;
+
+    setsid();
+
+    init_fs();
+    init_console();
+    init_term();
+
+    static sigset_t set;
+    sigfillset(&set);
+    sigprocmask(SIG_BLOCK, &set, NULL);
+
+    while (1) {
+        spawn("/etc/boot");
+        spawn("/etc/reboot");
+        sleep(1);
+    }
+
+    return 0;
+}