app/shim: separate signal handler implementation

Signed-off-by: Ophestra <cat@gensokyo.uk>

1 files changed, 48 insertions, 0 deletions

diff --git a/internal/app/shim-signal.c b/internal/app/shim-signal.c
new file mode 100644
index 00000000..b6120f1a
--- /dev/null
+++ b/internal/app/shim-signal.c
@@ -0,0 +1,48 @@
+#include "shim-signal.h"
+#include <errno.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+static pid_t hakurei_shim_param_ppid = -1;
+
+// this cannot unblock hlog since Go code is not async-signal-safe
+static void hakurei_shim_sigaction(int sig, siginfo_t *si, void *ucontext) {
+  if (sig != SIGCONT || si == NULL) {
+    // unreachable
+    fprintf(stderr, "sigaction: sa_sigaction got invalid siginfo\n");
+    return;
+  }
+
+  // monitor requests shim exit
+  if (si->si_pid == hakurei_shim_param_ppid)
+    exit(254);
+
+  fprintf(stderr, "sigaction: got SIGCONT from process %d\n", si->si_pid);
+
+  // shim orphaned before monitor delivers a signal
+  if (getppid() != hakurei_shim_param_ppid)
+    exit(3);
+}
+
+void hakurei_shim_setup_cont_signal(pid_t ppid) {
+  struct sigaction new_action = {0}, old_action = {0};
+  if (sigaction(SIGCONT, NULL, &old_action) != 0)
+    return;
+  if (old_action.sa_handler != SIG_DFL) {
+    errno = ENOTRECOVERABLE;
+    return;
+  }
+
+  new_action.sa_sigaction = hakurei_shim_sigaction;
+  if (sigemptyset(&new_action.sa_mask) != 0)
+    return;
+  new_action.sa_flags = SA_ONSTACK | SA_SIGINFO;
+
+  if (sigaction(SIGCONT, &new_action, NULL) != 0)
+    return;
+
+  errno = 0;
+  hakurei_shim_param_ppid = ppid;
+}