140 lines
4.3 KiB
C
140 lines
4.3 KiB
C
// extracted from https://raw.githubusercontent.com/Yelp/dumb-init/master/dumb-init.c
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#include <assert.h>
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#include <errno.h>
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#include <getopt.h>
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#include <signal.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/ioctl.h>
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#include <sys/types.h>
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#include <sys/wait.h>
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#include <unistd.h>
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#define PRINTERR(...) do { \
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fprintf(stderr, "[dumb-init] " __VA_ARGS__); \
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} while (0)
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#define DEBUG(...) do { \
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if (debug) { \
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PRINTERR(__VA_ARGS__); \
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} \
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} while (0)
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// Signals we care about are numbered from 1 to 31, inclusive.
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// (32 and above are real-time signals.)
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// TODO: this is likely not portable outside of Linux, or on strange architectures
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#define MAXSIG 31
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// Indices are one-indexed (signal 1 is at index 1). Index zero is unused.
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int signal_rewrite[MAXSIG + 1] = {[0 ... MAXSIG] = -1};
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pid_t child_pid = -1;
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char debug = 0;
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char use_setsid = 1;
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int translate_signal(int signum) {
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if (signum <= 0 || signum > MAXSIG) {
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return signum;
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} else {
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int translated = signal_rewrite[signum];
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if (translated == -1) {
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return signum;
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} else {
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DEBUG("Translating signal %d to %d.\n", signum, translated);
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return translated;
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}
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}
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}
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void forward_signal(int signum) {
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signum = translate_signal(signum);
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if (signum != 0) {
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kill(use_setsid ? -child_pid : child_pid, signum);
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DEBUG("Forwarded signal %d to children.\n", signum);
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} else {
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DEBUG("Not forwarding signal %d to children (ignored).\n", signum);
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}
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}
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/*
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* The dumb-init signal handler.
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*
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* The main job of this signal handler is to forward signals along to our child
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* process(es). In setsid mode, this means signaling the entire process group
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* rooted at our child. In non-setsid mode, this is just signaling the primary
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* child.
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*
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* In most cases, simply proxying the received signal is sufficient. If we
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* receive a job control signal, however, we should not only forward it, but
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* also sleep dumb-init itself.
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*
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* This allows users to run foreground processes using dumb-init and to
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* control them using normal shell job control features (e.g. Ctrl-Z to
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* generate a SIGTSTP and suspend the process).
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*
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* The libc manual is useful:
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* https://www.gnu.org/software/libc/manual/html_node/Job-Control-Signals.html
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*
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*/
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void handle_signal(int signum) {
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DEBUG("Received signal %d.\n", signum);
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if (signum == SIGCHLD) {
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int status, exit_status;
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pid_t killed_pid;
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while ((killed_pid = waitpid(-1, &status, WNOHANG)) > 0) {
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if (WIFEXITED(status)) {
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exit_status = WEXITSTATUS(status);
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DEBUG("A child with PID %d exited with exit status %d.\n", killed_pid, exit_status);
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} else {
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assert(WIFSIGNALED(status));
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exit_status = 128 + WTERMSIG(status);
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DEBUG("A child with PID %d was terminated by signal %d.\n", killed_pid, exit_status - 128);
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}
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if (killed_pid == child_pid) {
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forward_signal(SIGTERM); // send SIGTERM to any remaining children
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DEBUG("Child exited with status %d. Goodbye.\n", exit_status);
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exit(exit_status);
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}
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}
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} else {
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forward_signal(signum);
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if (signum == SIGTSTP || signum == SIGTTOU || signum == SIGTTIN) {
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DEBUG("Suspending self due to TTY signal.\n");
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kill(getpid(), SIGSTOP);
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}
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}
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}
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void set_rewrite_to_sigstop_if_not_defined(int signum) {
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if (signal_rewrite[signum] == -1)
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signal_rewrite[signum] = SIGSTOP;
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}
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// A dummy signal handler used for signals we care about.
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// On the FreeBSD kernel, ignored signals cannot be waited on by `sigwait` (but
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// they can be on Linux). We must provide a dummy handler.
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// https://lists.freebsd.org/pipermail/freebsd-ports/2009-October/057340.html
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void dummy(int signum) {}
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// ------------------------------------------------------------------------
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// Go entry point
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//
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void handleSignals() {
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sigset_t all_signals;
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sigfillset(&all_signals);
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sigprocmask(SIG_BLOCK, &all_signals, NULL);
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int i = 0;
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for (i = 1; i <= MAXSIG; i++)
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signal(i, dummy);
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for (;;) {
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int signum;
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sigwait(&all_signals, &signum);
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handle_signal(signum);
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}
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}
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