Add disk_folders to disk-load: no tool said which folders fill a disk (issue 1804)

modules/disk-load/cmd/disk-load/machine.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"fmt"
+	"io/fs"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -53,6 +54,13 @@ type Machine struct {
 	Run    Runner
 	Wait   func(time.Duration)
 	Statfs func(path string) (FSStat, error)
+
+	// The folder walk's seams, all optional: the folder reader, the filesystem a path is on, the clock and
+	// the time the walk may take (60 s when zero).
+	ReadDir func(path string) ([]os.DirEntry, error)
+	DevOf   func(path string, info fs.FileInfo) uint64
+	Clock   func() time.Time
+	Budget  time.Duration
 }
 
 // Here is the machine this process runs on.