internal/outcome/shim: move signal constants

The magic numbers hurt readability.

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

internal/outcome/shim-signal.c

@@ -8,35 +8,32 @@
 static pid_t hakurei_shim_param_ppid = -1;
 static int hakurei_shim_fd = -1;
 
-static ssize_t hakurei_shim_write(const void *buf, size_t count) {
+/* see shim.go for handling of the message */
+static inline ssize_t hakurei_shim_write(hakurei_shim_msg msg) {
   int savedErrno = errno;
-  ssize_t ret = write(hakurei_shim_fd, buf, count);
+  unsigned char buf = (unsigned char)msg;
+  ssize_t ret = write(hakurei_shim_fd, &buf, 1);
   if (ret == -1 && errno != EAGAIN)
     exit(EXIT_FAILURE);
   errno = savedErrno;
   return ret;
 }
 
-/* see shim_linux.go for handling of the value */
 static void hakurei_shim_sigaction(int sig, siginfo_t *si, void *ucontext) {
   if (sig != SIGCONT || si == NULL) {
-    /* unreachable */
+    hakurei_shim_write(HAKUREI_SHIM_INVALID);
-    hakurei_shim_write("\2", 1);
     return;
   }
 
   if (si->si_pid == hakurei_shim_param_ppid) {
-    /* monitor requests shim exit */
+    hakurei_shim_write(HAKUREI_SHIM_EXIT_REQUESTED);
-    hakurei_shim_write("\0", 1);
     return;
   }
 
-  /* unexpected si_pid */
+  hakurei_shim_write(HAKUREI_SHIM_BAD_PID);
-  hakurei_shim_write("\3", 1);
 
   if (getppid() != hakurei_shim_param_ppid)
-    /* shim orphaned before monitor delivers a signal */
+    hakurei_shim_write(HAKUREI_SHIM_ORPHAN);
-    hakurei_shim_write("\1", 1);
 }
 
 void hakurei_shim_setup_cont_signal(pid_t ppid, int fd) {

internal/outcome/shim-signal.h

@@ -1,3 +1,11 @@
 #include <signal.h>
 
+/* see shim.go for documentation */
+typedef enum {
+  HAKUREI_SHIM_EXIT_REQUESTED,
+  HAKUREI_SHIM_ORPHAN,
+  HAKUREI_SHIM_INVALID,
+  HAKUREI_SHIM_BAD_PID,
+} hakurei_shim_msg;
+
 void hakurei_shim_setup_cont_signal(pid_t ppid, int fd);

internal/outcome/shim.go

@@ -22,6 +22,17 @@ import (
 //#include "shim-signal.h"
 import "C"
 
+const (
+	/* hakurei requests shim exit */
+	shimMsgExitRequested = C.HAKUREI_SHIM_EXIT_REQUESTED
+	/* shim orphaned before hakurei delivers a signal */
+	shimMsgOrphaned = C.HAKUREI_SHIM_ORPHAN
+	/* unreachable */
+	shimMsgInvalid = C.HAKUREI_SHIM_INVALID
+	/* unexpected si_pid */
+	shimMsgBadPID = C.HAKUREI_SHIM_BAD_PID
+)
+
 // setupContSignal sets up the SIGCONT signal handler for the cross-uid shim exit hack.
 // The signal handler is implemented in C, signals can be processed by reading from the returned reader.
 // The returned function must be called after all signal processing concludes.
@@ -161,7 +172,7 @@ func shimEntrypoint(k syscallDispatcher) {
 			}
 
 			switch buf[0] {
-			case 0: // got SIGCONT from monitor: shim exit requested
+			case shimMsgExitRequested: // got SIGCONT from hakurei: shim exit requested
 				if fp := cancelContainer.Load(); stateParams.params.ForwardCancel && fp != nil && *fp != nil {
 					(*fp)()
 					// shim now bound by ShimWaitDelay, implemented below
@@ -171,13 +182,13 @@ func shimEntrypoint(k syscallDispatcher) {
 				// setup has not completed, terminate immediately
 				k.exit(hst.ExitRequest)
 
-			case 1: // got SIGCONT via pdeath_signal: monitor died before delivering signal
+			case shimMsgOrphaned: // got SIGCONT after orphaned: hakurei died before delivering signal
 				k.exit(hst.ExitOrphan)
 
-			case 2: // unreachable
+			case shimMsgInvalid: // unreachable
 				msg.Verbose("sa_sigaction got invalid siginfo")
 
-			case 3: // got SIGCONT from unexpected process: hopefully the terminal driver
+			case shimMsgBadPID: // got SIGCONT from unexpected process: hopefully the terminal driver
 				msg.Verbose("got SIGCONT from unexpected process")
 
 			default: // unreachable

internal/outcome/shim_test.go

@@ -148,9 +148,9 @@ func TestShimEntrypoint(t *testing.T) {
 			// deferred
 			call("wKeepAlive", stub.ExpectArgs{}, nil, nil),
 		}, Tracks: []stub.Expect{{Calls: []stub.Call{
-			call("rcRead", stub.ExpectArgs{}, []byte{2}, nil),
+			call("rcRead", stub.ExpectArgs{}, []byte{shimMsgInvalid}, nil),
 			call("verbose", stub.ExpectArgs{[]any{"sa_sigaction got invalid siginfo"}}, nil, nil),
-			call("rcRead", stub.ExpectArgs{}, []byte{3}, nil),
+			call("rcRead", stub.ExpectArgs{}, []byte{shimMsgBadPID}, nil),
 			call("verbose", stub.ExpectArgs{[]any{"got SIGCONT from unexpected process"}}, nil, nil),
 			call("rcRead", stub.ExpectArgs{}, nil, nil), // stub terminates this goroutine
 		}}}}, nil},