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/manager.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/gob"
 	"errors"
+	"log"
 	"os"
 	"os/exec"
 	"strconv"
@@ -54,8 +55,7 @@ func (s *Shim) Start(
 	// prepare user switcher invocation
 	var fsu string
 	if p, ok := internal.Path(internal.Fsu); !ok {
-		fmsg.Fatal("invalid fsu path, this copy of fortify is not compiled correctly")
-		panic("unreachable")
+		log.Fatal("invalid fsu path, this copy of fortify is not compiled correctly")
 	} else {
 		fsu = p
 	}
@@ -75,7 +75,7 @@ func (s *Shim) Start(
 
 	// format fsu supplementary groups
 	if len(supp) > 0 {
-		fmsg.VPrintf("attaching supplementary group ids %s", supp)
+		fmsg.Verbosef("attaching supplementary group ids %s", supp)
 		s.cmd.Env = append(s.cmd.Env, "FORTIFY_GROUPS="+strings.Join(supp, " "))
 	}
 	s.cmd.Stdin, s.cmd.Stdout, s.cmd.Stderr = os.Stdin, os.Stdout, os.Stderr
@@ -87,7 +87,7 @@ func (s *Shim) Start(
 		s.sync = &fd
 	}
 
-	fmsg.VPrintln("starting shim via fsu:", s.cmd)
+	fmsg.Verbose("starting shim via fsu:", s.cmd)
 	// withhold messages to stderr
 	fmsg.Suspend()
 	if err := s.cmd.Start(); err != nil {