contrib/fs-idmap: Move logic to a new function

We can't call log.Fatalf() and defer functions, as the former doesn't
call any defers. Let's just move the code to a new function and call
os.Exit() only in main, when all defer executed.

Signed-off-by: Rodrigo Campos <[email protected]>

Author: rata

contrib/cmd/fs-idmap/fs-idmap.go

@@ -14,11 +14,16 @@ func main() {
 	if len(os.Args) != 2 {
 		log.Fatalf("usage: %s path_to_mount_set_attr", os.Args[0])
 	}
-
 	src := os.Args[1]
+	if err := supportsIDMap(src); err != nil {
+		log.Fatalf("fatal error: %v", err)
+	}
+}
+
+func supportsIDMap(src string) error {
 	treeFD, err := unix.OpenTree(unix.AT_FDCWD, src, uint(unix.OPEN_TREE_CLONE|unix.OPEN_TREE_CLOEXEC|unix.AT_EMPTY_PATH))
 	if err != nil {
-		log.Fatalf("error calling open_tree %q: %v", src, err)
+		return fmt.Errorf("error calling open_tree %q: %w", src, err)
 	}
 	defer unix.Close(treeFD)
 
@@ -29,7 +34,7 @@ func main() {
 		GidMappings: []syscall.SysProcIDMap{{ContainerID: 0, HostID: 65536, Size: 65536}},
 	}
 	if err := cmd.Start(); err != nil {
-		log.Fatalf("failed to run the helper binary: %v", err)
+		return fmt.Errorf("failed to run the helper binary: %w", err)
 	}
 	defer func() {
 		_ = cmd.Process.Kill()
@@ -39,7 +44,7 @@ func main() {
 	path := fmt.Sprintf("/proc/%d/ns/user", cmd.Process.Pid)
 	var userNsFile *os.File
 	if userNsFile, err = os.Open(path); err != nil {
-		log.Fatalf("unable to get user ns file descriptor: %v", err)
+		return fmt.Errorf("unable to get user ns file descriptor: %w", err)
 	}
 	defer userNsFile.Close()
 
@@ -48,6 +53,8 @@ func main() {
 		Userns_fd: uint64(userNsFile.Fd()),
 	}
 	if err := unix.MountSetattr(treeFD, "", unix.AT_EMPTY_PATH, &attr); err != nil {
-		log.Fatalf("error calling mount_setattr: %v", err)
+		fmt.Errorf("error calling mount_setattr: %w", err)
 	}
+
+	return nil
 }