SchOS/cmd/schinit/main.c

// SPDX-License-Identifier: Apache-2.0
//
// schinit — SchOS process 1.
//
// Shaped after launchd rather than sysvinit, and the reason is not the config
// format. It is *demand launching*: the supervisor holds the listening socket
// or watches the path, and starts a job when something actually arrives. That
// inverts the dependency graph — a job stops needing to declare what must be
// running before it, because the thing it depends on answers on first use, and
// runlevels stop being a concept at all.
//
// This is milestone 1: manifests, RunAtLoad, KeepAlive with backoff, and
// reaping. Sockets are parsed and remembered but not yet held; that is
// milestone 2, and the manifest format already has a place to say it.
//
// Constraints worth knowing before editing. This program links against lib/,
// which is raw syscall stubs — there is no libc here. No malloc, no printf, no
// strlen. Everything is static storage and hand-rolled, which is also why the
// limits below are constants rather than growable.

#include "types.h"
#include "user.h"
#include "fcntl.h"
#include "posix.h"   // TIOCSCTTY, TIOCSPGRP

#define MAXJOBS      32
#define MAXARGS      16
#define MAXLABEL     64
#define MAXPATH     128
#define MAXLINE     256
#define JOBDIR      "/etc/schinit"

// ---------------------------------------------------------------------------
// Small string helpers. No libc.
// ---------------------------------------------------------------------------

static int
slen(const char *s)
{
    int n = 0;
    while (s[n]) n++;
    return n;
}

static void
scopy(char *dst, const char *src, int cap)
{
    int i = 0;
    while (src[i] && i < cap - 1) { dst[i] = src[i]; i++; }
    dst[i] = '\0';
}

static int
seq(const char *a, const char *b)
{
    while (*a && *a == *b) { a++; b++; }
    return *a == *b;
}

// Case-insensitive, so a manifest may say KeepAlive, keepalive or KEEPALIVE.
// Keys are for humans and this is not a language.
static int
sieq(const char *a, const char *b)
{
    for (;;) {
        char ca = *a, cb = *b;
        if (ca >= 'A' && ca <= 'Z') ca += 32;
        if (cb >= 'A' && cb <= 'Z') cb += 32;
        if (ca != cb) return 0;
        if (!ca) return 1;
        a++; b++;
    }
}

static int
ends_with(const char *s, const char *suffix)
{
    int ls = slen(s), lf = slen(suffix);
    if (lf > ls) return 0;
    return seq(s + ls - lf, suffix);
}

static void
out(const char *s)
{
    write(1, (void *)s, slen(s));
}

static void
outn(int v)
{
    char buf[12];
    int i = 11;
    int neg = v < 0;
    if (neg) v = -v;
    buf[i--] = '\0';
    if (v == 0) buf[i--] = '0';
    while (v > 0) { buf[i--] = (char)('0' + v % 10); v /= 10; }
    if (neg) buf[i--] = '-';
    out(&buf[i + 1]);
}

// ---------------------------------------------------------------------------
// Jobs
// ---------------------------------------------------------------------------

struct job {
    char label[MAXLABEL];
    char program[MAXPATH];
    char *argv[MAXARGS + 1];
    char argstore[MAXLINE];

    char stdin_path[MAXPATH];
    char stdout_path[MAXPATH];
    char stderr_path[MAXPATH];

    int  run_at_load;
    int  keep_alive;
    int  disabled;
    int  throttle;          // seconds between respawns
    int  own_tty;           // claim the console as controlling terminal

    // A socket the job wants schinit to hold. Parsed now, honoured in
    // milestone 2 -- recorded here so the manifest format does not have to
    // change when it is.
    char sock_path[MAXPATH];

    int  pid;               // 0 when not running
    int  last_start;        // uptime() ticks, for throttling
    int  starts;
};

static struct job jobs[MAXJOBS];
static int njobs;

static void
job_defaults(struct job *j)
{
    j->label[0] = j->program[0] = '\0';
    j->stdin_path[0] = j->stdout_path[0] = j->stderr_path[0] = '\0';
    j->sock_path[0] = '\0';
    j->argstore[0] = '\0';
    j->argv[0] = 0;
    j->run_at_load = 0;
    j->keep_alive  = 0;
    j->disabled    = 0;
    j->throttle    = 1;
    j->own_tty     = 0;
    j->pid = 0;
    j->last_start = 0;
    j->starts = 0;
}

static int
truthy(const char *v)
{
    return sieq(v, "yes") || sieq(v, "true") || sieq(v, "1") || sieq(v, "on");
}

static int
parse_int(const char *s)
{
    int v = 0;
    while (*s >= '0' && *s <= '9') { v = v * 10 + (*s - '0'); s++; }
    return v;
}

// Split Args into argv, in place within the job's own storage. argv[0] is the
// program's name as it should see it, which is conventionally the basename and
// not the full path -- so a manifest says `Args = sh` for `/bin/sh`.
static void
split_args(struct job *j, const char *value)
{
    scopy(j->argstore, value, MAXLINE);
    int n = 0;
    char *p = j->argstore;
    while (*p && n < MAXARGS) {
        while (*p == ' ' || *p == '\t') p++;
        if (!*p) break;
        j->argv[n++] = p;
        while (*p && *p != ' ' && *p != '\t') p++;
        if (*p) *p++ = '\0';
    }
    j->argv[n] = 0;
}

// ---------------------------------------------------------------------------
// Manifest parsing
//
// Sectioned key = value. Comments start with #. A [Socket name] section marks
// everything after it as belonging to that socket, which is why Path is read
// into sock_path rather than treated as a job key.
// ---------------------------------------------------------------------------

static char *
trim(char *s)
{
    while (*s == ' ' || *s == '\t') s++;
    int n = slen(s);
    while (n > 0 && (s[n-1] == ' ' || s[n-1] == '\t' ||
                     s[n-1] == '\r' || s[n-1] == '\n'))
        s[--n] = '\0';
    return s;
}

static int
load_job(const char *path)
{
    if (njobs >= MAXJOBS) {
        out("schinit: too many jobs, ignoring "); out(path); out("\n");
        return -1;
    }

    int fd = open((char *)path, O_RDONLY);
    if (fd < 0) return -1;

    // Whole file into one static buffer. A job manifest that does not fit in
    // 4 KB is a manifest doing something it should not.
    static char buf[4096];
    int n = read(fd, buf, sizeof(buf) - 1);
    close(fd);
    if (n <= 0) return -1;
    buf[n] = '\0';

    struct job *j = &jobs[njobs];
    job_defaults(j);

    int in_socket = 0;
    char *p = buf;
    while (*p) {
        char *line = p;
        while (*p && *p != '\n') p++;
        if (*p) *p++ = '\0';

        // Strip comments before trimming, so trailing comments work too.
        for (char *c = line; *c; c++)
            if (*c == '#') { *c = '\0'; break; }

        line = trim(line);
        if (!*line) continue;

        if (line[0] == '[') {
            // [Socket name] -- the only section kind for now. Anything else is
            // ignored rather than fatal: an unknown section from a newer
            // schinit should not stop this one booting the machine.
            in_socket = (line[1] == 'S' || line[1] == 's');
            continue;
        }

        char *eq = line;
        while (*eq && *eq != '=') eq++;
        if (!*eq) continue;                 // not key = value; skip
        *eq = '\0';
        char *key = trim(line);
        char *val = trim(eq + 1);

        if (in_socket) {
            if (sieq(key, "Path")) scopy(j->sock_path, val, MAXPATH);
            continue;
        }

        if      (sieq(key, "Label"))          scopy(j->label, val, MAXLABEL);
        else if (sieq(key, "Program"))        scopy(j->program, val, MAXPATH);
        else if (sieq(key, "Args"))           split_args(j, val);
        else if (sieq(key, "RunAtLoad"))      j->run_at_load = truthy(val);
        else if (sieq(key, "KeepAlive"))      j->keep_alive = truthy(val);
        else if (sieq(key, "Disabled"))       j->disabled = truthy(val);
        else if (sieq(key, "ThrottleInterval")) j->throttle = parse_int(val);
        else if (sieq(key, "ControllingTerminal")) j->own_tty = truthy(val);
        else if (sieq(key, "StandardIn"))     scopy(j->stdin_path, val, MAXPATH);
        else if (sieq(key, "StandardOut"))    scopy(j->stdout_path, val, MAXPATH);
        else if (sieq(key, "StandardError"))  scopy(j->stderr_path, val, MAXPATH);
        // Unknown keys are ignored on purpose, same reasoning as sections.
    }

    if (!j->program[0]) {
        out("schinit: "); out(path); out(": no Program, ignoring\n");
        return -1;
    }
    if (!j->label[0])
        scopy(j->label, j->program, MAXLABEL);
    if (!j->argv[0]) {
        // No Args given: pass the program path as argv[0], which is what a
        // program expects when nothing better is said.
        scopy(j->argstore, j->program, MAXLINE);
        j->argv[0] = j->argstore;
        j->argv[1] = 0;
    }
    if (j->throttle <= 0)
        j->throttle = 1;

    njobs++;
    return 0;
}

// Read every *.job in JOBDIR. getdents64 rather than a hardcoded list, so
// dropping a file in the directory is all it takes to add a job.
static void
load_jobs(void)
{
    int fd = open(JOBDIR, O_RDONLY);
    if (fd < 0) {
        out("schinit: no " JOBDIR "\n");
        return;
    }

    static char dbuf[4096];
    for (;;) {
        int n = getdents64(fd, dbuf, sizeof(dbuf));
        if (n <= 0) break;

        int off = 0;
        while (off < n) {
            struct dirent64 *d = (struct dirent64 *)(dbuf + off);
            // Step by d_reclen: records are packed and variable length.
            if (d->d_reclen == 0) break;
            off += d->d_reclen;

            if (d->d_name[0] == '.') continue;
            if (!ends_with(d->d_name, ".job")) continue;

            char path[MAXPATH];
            scopy(path, JOBDIR "/", MAXPATH);
            int at = slen(path);
            scopy(path + at, d->d_name, MAXPATH - at);
            load_job(path);
        }
    }
    close(fd);
}

// ---------------------------------------------------------------------------
// Starting and supervising
// ---------------------------------------------------------------------------

static void
redirect(const char *path, int fd, int flags)
{
    if (!path[0]) return;
    int f = open((char *)path, flags);
    if (f < 0) return;
    if (f != fd) { dup2(f, fd); close(f); }
}

static void
start_job(struct job *j)
{
    int pid = fork();
    if (pid < 0) {
        out("schinit: fork failed for "); out(j->label); out("\n");
        return;
    }

    if (pid == 0) {
        // Its own session, so a job cannot reach back and signal the rest of
        // the system through a shared controlling terminal.
        setsid();

        redirect(j->stdin_path,  0, O_RDWR);
        redirect(j->stdout_path, 1, O_RDWR);
        redirect(j->stderr_path, 2, O_RDWR);

        // A job that reads the console has to *own* it, and setsid() is what
        // makes that necessary: a fresh session has no controlling terminal,
        // and the console only delivers input to the foreground process group
        // it is tracking. Without this the shell came up, echoed every
        // keystroke through the line discipline, and executed none of them --
        // which looks like a hung shell and is really a terminal that is not
        // listening to it.
        //
        // Off by default. A daemon has no business seizing the console, and
        // launchd's model is that the console is a thing a job asks for.
        if (j->own_tty) {
            int pg = getpid();          // after setsid(), pgid == pid
            ioctl(0, TIOCSCTTY, 0);
            ioctl(0, TIOCSPGRP, &pg);
        }

        // exec.c enables the Linux ABI automatically for musl binaries. Do NOT
        // call enable_linux_abi() here: it would renumber the syscalls this
        // child still has to make.
        exec(j->program, j->argv);

        out("schinit: cannot exec "); out(j->program);
        out(" for "); out(j->label); out("\n");
        exit();
    }

    j->pid = pid;
    j->last_start = uptime();
    j->starts++;
}

static struct job *
job_by_pid(int pid)
{
    for (int i = 0; i < njobs; i++)
        if (jobs[i].pid == pid)
            return &jobs[i];
    return 0;
}

// ---------------------------------------------------------------------------
// Bootstrap: the device nodes and mounts that must exist before anything runs.
//
// Not jobs. A job needs /dev/console to have somewhere to send its output, so
// this cannot itself be expressed as one without a bootstrapping problem.
// ---------------------------------------------------------------------------

static void
bootstrap(void)
{
    // /dev before the console, because the console now lives in it.
    //
    // The old order was the other way round -- open a console first so every
    // message below had somewhere to go -- and the fallback below is what keeps
    // that guarantee. If the mount fails there is no /dev/console and no way to
    // say so, so the original path stays: a node called `console` in the root
    // directory, which is where this used to put one.
    //
    // /dev is a filesystem now, not a pile of nodes. Every major and minor it
    // contains is the kernel's -- devsw[] in kernel/dev/cdev.c is what they
    // dispatch on -- and this program used to hold a second copy of that
    // mapping with nothing checking the two agreed.
    //
    // It was also slow in a way that only showed on a fresh image: each mknod
    // was one SchFS transaction, and the twenty of them cost 2600 ms of the
    // first boot before this program printed its first line. On a second boot
    // the nodes already existed and the same code took 0 ms, so the cost was
    // invisible to anyone not building images -- which is to say, invisible to
    // everyone except whoever works on this.
    mkdir("/dev");
    mount("dev", "/dev", "devtmpfs", 0, 0);

    if (open("/dev/console", O_RDWR) < 0) {
        // No devtmpfs. Fall back to a real node on the root filesystem, which
        // is what every boot did before this.
        if (open("console", O_RDWR) < 0) {
            mknod("console", 1, 1);
            open("console", O_RDWR);
        }
    }
    dup(0);
    dup(0);

    // /proc is a real filesystem (kernel/fs/procfs.c), not a handful of nodes:
    // it has to be, because one directory per process cannot be created ahead
    // of time. That is what makes ps and top work.
    //
    // The thirteen mknod() calls that used to follow this mount are gone. They
    // ran *after* it, so every one of them was resolving a path into a
    // read-only synthetic filesystem and failing -- dead weight kept as a
    // fallback for a mount that has not failed in a long time, exactly as the
    // note in procfs.c said it was.
    mkdir("/proc");
    mount("proc", "/proc", "proc", 0, 0);

    // Mount points, and nothing mounts on them yet. They are created by the
    // image builder (see sysroot-install), so these are a fallback for an image
    // that does not have them -- a mkdir that fails because the directory is
    // already there costs a path walk and no writes, where creating one costs a
    // whole SchFS transaction.
    mkdir("/sys");
    mkdir("/run");
}

// ---------------------------------------------------------------------------

int
main(void)
{
    if (getpid() != 1)
        exit();

    bootstrap();

    out("schinit: SchOS process 1\n");

    load_jobs();

    if (njobs == 0) {
        // Nothing to supervise. Rather than idle usefully-looking, say so and
        // fall back to a shell -- an unbootable-looking machine because a
        // manifest was missing would be a poor trade for purity.
        out("schinit: no jobs found; falling back to /bin/sh\n");
        struct job *j = &jobs[njobs++];
        job_defaults(j);
        scopy(j->label, "os.schos.fallback-shell", MAXLABEL);
        scopy(j->program, "/bin/sh", MAXPATH);
        split_args(j, "sh");
        scopy(j->stdin_path,  "/dev/console", MAXPATH);
        scopy(j->stdout_path, "/dev/console", MAXPATH);
        scopy(j->stderr_path, "/dev/console", MAXPATH);
        j->run_at_load = 1;
        j->keep_alive  = 1;
        j->own_tty     = 1;
    }

    out("schinit: "); outn(njobs); out(" job");
    if (njobs != 1) out("s");
    out(" loaded\n");

    for (int i = 0; i < njobs; i++) {
        struct job *j = &jobs[i];
        if (j->disabled || !j->run_at_load) continue;
        out("schinit: starting "); out(j->label); out("\n");
        start_job(j);
    }

    out("schinit: ready (pid 1)\n");

    // Supervision loop.
    //
    // wait() reaps whatever exited, including processes reparented here when
    // their own parent died -- those are not jobs and job_by_pid returns 0 for
    // them, which is the whole handling they need.
    for (;;) {
        int pid = wait();
        if (pid < 0) {
            // Nothing left to wait for. Should not happen while any job is
            // alive; sleep rather than spin so a mistake here costs a idle
            // machine and not a hot CPU.
            sleep(100);
            continue;
        }

        struct job *j = job_by_pid(pid);
        if (!j) continue;                   // an adopted orphan; already reaped

        j->pid = 0;

        if (!j->keep_alive) {
            out("schinit: "); out(j->label); out(" exited\n");
            continue;
        }

        // Throttle. A job that exits immediately and forever would otherwise
        // spin the machine; launchd's ThrottleInterval exists for exactly this
        // and defaults to 10 seconds. One is enough here, where the common
        // case is a shell someone just exited on purpose and expects back.
        int since = uptime() - j->last_start;
        int ticks = j->throttle * 100;      // uptime() counts 10ms ticks
        if (since < ticks)
            sleep(ticks - since);

        start_job(j);
    }

    return 0;
}