vfs: --vfs-used-is-size uses `rclone size` to give used space (full recursive listing)

The same algorithm as `rclone size` is used, but without filtering.
It is advised to only use this with caching.

cmd/mountlib/mount.go

@@ -260,6 +260,19 @@ This is the same as setting the attr_timeout option in mount.fuse.
 Note that all the rclone filters can be used to select a subset of the
 files to be visible in the mount.
 
+### Alternate report of used bytes
+
+Some backends, most notably S3, do not report the amount of bytes used.
+If you need this information to be available when running ` + "`df`" + ` on the filesystem,
+then pass the parameter “--vfs-used-is-size=true” to rclone.
+With this parameter set, instead of relying on the backend to report this information,
+rclone will scan the whole remote like ` + "`rclone size …`" + ` does, and compute the total used space itself.
+
+Notes:
+
+* Contrary to ` + "`rclone size …`" + `, this flag ignores filters so that the result is accurate.
+* It is advised to only use this with caching.
+
 ### systemd
 
 When running rclone ` + commandName + ` as a systemd service, it is possible

vfs/vfs.go

@@ -35,6 +35,7 @@ import (
 
 	"github.com/rclone/rclone/fs"
 	"github.com/rclone/rclone/fs/log"
+	"github.com/rclone/rclone/fs/walk"
 	"github.com/rclone/rclone/vfs/vfscache"
 	"github.com/rclone/rclone/vfs/vfscommon"
 )
@@ -478,9 +479,25 @@ func (vfs *VFS) Statfs() (total, used, free int64) {
 	defer vfs.usageMu.Unlock()
 	total, used, free = -1, -1, -1
 	doAbout := vfs.f.Features().About
-	if doAbout != nil && (vfs.usageTime.IsZero() || time.Since(vfs.usageTime) >= vfs.Opt.DirCacheTime) {
+	if (doAbout != nil || vfs.Opt.UsedIsSize) && (vfs.usageTime.IsZero() || time.Since(vfs.usageTime) >= vfs.Opt.DirCacheTime) {
 		var err error
-		vfs.usage, err = doAbout(context.TODO())
+		ctx := context.TODO()
+		if doAbout == nil {
+			vfs.usage = &fs.Usage{}
+		} else {
+			vfs.usage, err = doAbout(ctx)
+		}
+		if vfs.Opt.UsedIsSize {
+			var usedBySizeAlgorithm int64 = 0
+			// Algorithm from `rclone size`
+			err = walk.ListR(ctx, vfs.f, "", true, -1, walk.ListObjects, func(entries fs.DirEntries) error {
+				entries.ForObject(func(o fs.Object) {
+					usedBySizeAlgorithm += o.Size()
+				})
+				return nil
+			})
+			vfs.usage.Used = &usedBySizeAlgorithm
+		}
 		vfs.usageTime = time.Now()
 		if err != nil {
 			fs.Errorf(vfs.f, "Statfs failed: %v", err)

vfs/vfscommon/options.go

@@ -30,6 +30,7 @@ type Options struct {
 	CaseInsensitive   bool
 	WriteWait         time.Duration // time to wait for in-sequence write
 	ReadWait          time.Duration // time to wait for in-sequence read
+	UsedIsSize        bool          // if true, use the `rclone size` algorithm for Used size
 }
 
 // DefaultOpt is the default values uses for Opt
@@ -54,4 +55,5 @@ var DefaultOpt = Options{
 	CaseInsensitive:   runtime.GOOS == "windows" || runtime.GOOS == "darwin", // default to true on Windows and Mac, false otherwise
 	WriteWait:         1000 * time.Millisecond,
 	ReadWait:          5 * time.Millisecond,
+	UsedIsSize:        false,
 }

vfs/vfsflags/vfsflags.go

@@ -35,5 +35,6 @@ func AddFlags(flagSet *pflag.FlagSet) {
 	flags.BoolVarP(flagSet, &Opt.CaseInsensitive, "vfs-case-insensitive", "", Opt.CaseInsensitive, "If a file name not found, find a case insensitive match.")
 	flags.DurationVarP(flagSet, &Opt.WriteWait, "vfs-write-wait", "", Opt.WriteWait, "Time to wait for in-sequence write before giving error.")
 	flags.DurationVarP(flagSet, &Opt.ReadWait, "vfs-read-wait", "", Opt.ReadWait, "Time to wait for in-sequence read before seeking.")
+	flags.BoolVarP(flagSet, &Opt.UsedIsSize, "vfs-used-is-size", "", Opt.UsedIsSize, "Use the `rclone size` algorithm for Used size.")
 	platformFlags(flagSet)
 }