fmsg: implement suspend in writer

This removes the requirement to call fmsg.Exit on every exit path, and enables direct use of the "log" package. However, fmsg.BeforeExit is still encouraged when possible to catch exit on suspended output.

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

internal/app/shim/main.go

@@ -3,6 +3,7 @@ package shim
 import (
 	"context"
 	"errors"
+	"log"
 	"os"
 	"os/exec"
 	"os/signal"
@@ -25,12 +26,11 @@ import (
 func Main() {
 	// sharing stdout with fortify
 	// USE WITH CAUTION
-	fmsg.SetPrefix("shim")
+	fmsg.Prepare("shim")
 
 	// setting this prevents ptrace
 	if err := internal.PR_SET_DUMPABLE__SUID_DUMP_DISABLE(); err != nil {
-		fmsg.Fatalf("cannot set SUID_DUMP_DISABLE: %s", err)
-		panic("unreachable")
+		log.Fatalf("cannot set SUID_DUMP_DISABLE: %s", err)
 	}
 
 	// receive setup payload
@@ -40,21 +40,20 @@ func Main() {
 	)
 	if f, err := proc.Receive(Env, &payload); err != nil {
 		if errors.Is(err, proc.ErrInvalid) {
-			fmsg.Fatal("invalid config descriptor")
+			log.Fatal("invalid config descriptor")
 		}
 		if errors.Is(err, proc.ErrNotSet) {
-			fmsg.Fatal("FORTIFY_SHIM not set")
+			log.Fatal("FORTIFY_SHIM not set")
 		}
 
-		fmsg.Fatalf("cannot decode shim setup payload: %v", err)
-		panic("unreachable")
+		log.Fatalf("cannot decode shim setup payload: %v", err)
 	} else {
-		fmsg.SetVerbose(payload.Verbose)
+		fmsg.Store(payload.Verbose)
 		closeSetup = f
 	}
 
 	if payload.Bwrap == nil {
-		fmsg.Fatal("bwrap config not supplied")
+		log.Fatal("bwrap config not supplied")
 	}
 
 	// restore bwrap sync fd
@@ -65,7 +64,7 @@ func Main() {
 
 	// close setup socket
 	if err := closeSetup(); err != nil {
-		fmsg.Println("cannot close setup pipe:", err)
+		log.Println("cannot close setup pipe:", err)
 		// not fatal
 	}
 
@@ -73,15 +72,15 @@ func Main() {
 	if s, err := os.Stat(payload.Home); err != nil {
 		if os.IsNotExist(err) {
 			if err = os.Mkdir(payload.Home, 0700); err != nil {
-				fmsg.Fatalf("cannot create home directory: %v", err)
+				log.Fatalf("cannot create home directory: %v", err)
 			}
 		} else {
-			fmsg.Fatalf("cannot access home directory: %v", err)
+			log.Fatalf("cannot access home directory: %v", err)
 		}
 
 		// home directory is created, proceed
 	} else if !s.IsDir() {
-		fmsg.Fatalf("data path %q is not a directory", payload.Home)
+		log.Fatalf("data path %q is not a directory", payload.Home)
 	}
 
 	var ic init0.Payload
@@ -95,10 +94,10 @@ func Main() {
 		// no argv, look up shell instead
 		var ok bool
 		if payload.Bwrap.SetEnv == nil {
-			fmsg.Fatal("no command was specified and environment is unset")
+			log.Fatal("no command was specified and environment is unset")
 		}
 		if ic.Argv0, ok = payload.Bwrap.SetEnv["SHELL"]; !ok {
-			fmsg.Fatal("no command was specified and $SHELL was unset")
+			log.Fatal("no command was specified and $SHELL was unset")
 		}
 
 		ic.Argv = []string{ic.Argv0}
@@ -110,20 +109,20 @@ func Main() {
 
 	// serve setup payload
 	if fd, encoder, err := proc.Setup(&extraFiles); err != nil {
-		fmsg.Fatalf("cannot pipe: %v", err)
+		log.Fatalf("cannot pipe: %v", err)
 	} else {
 		conf.SetEnv[init0.Env] = strconv.Itoa(fd)
 		go func() {
-			fmsg.VPrintln("transmitting config to init")
+			fmsg.Verbose("transmitting config to init")
 			if err = encoder.Encode(&ic); err != nil {
-				fmsg.Fatalf("cannot transmit init config: %v", err)
+				log.Fatalf("cannot transmit init config: %v", err)
 			}
 		}()
 	}
 
 	helper.BubblewrapName = payload.Exec[0] // resolved bwrap path by parent
-	if fmsg.Verbose() {
-		seccomp.CPrintln = fmsg.Println
+	if fmsg.Load() {
+		seccomp.CPrintln = log.Println
 	}
 	if b, err := helper.NewBwrap(
 		conf, path.Join(fst.Tmp, "sbin/init"),
@@ -131,7 +130,7 @@ func Main() {
 		extraFiles,
 		syncFd,
 	); err != nil {
-		fmsg.Fatalf("malformed sandbox config: %v", err)
+		log.Fatalf("malformed sandbox config: %v", err)
 	} else {
 		b.Stdin(os.Stdin).Stdout(os.Stdout).Stderr(os.Stderr)
 		ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
@@ -139,15 +138,15 @@ func Main() {
 
 		// run and pass through exit code
 		if err = b.Start(ctx, false); err != nil {
-			fmsg.Fatalf("cannot start target process: %v", err)
+			log.Fatalf("cannot start target process: %v", err)
 		} else if err = b.Wait(); err != nil {
 			var exitError *exec.ExitError
 			if !errors.As(err, &exitError) {
-				fmsg.Println("wait:", err)
-				fmsg.Exit(127)
+				log.Printf("wait: %v", err)
+				internal.Exit(127)
 				panic("unreachable")
 			}
-			fmsg.Exit(exitError.ExitCode())
+			internal.Exit(exitError.ExitCode())
 			panic("unreachable")
 		}
 	}