vfs: add --vfs-disk-space-total-size option to manually set the total disk space

Now you can specify --vfs-disk-space-total-size to set the total disk
space (default to -1)

fixes #3270

vfs/help.go

@@ -307,6 +307,13 @@ If the flag is not provided on the command line, then its default value depends
 on the operating system where rclone runs: "true" on Windows and macOS, "false"
 otherwise. If the flag is provided without a value, then it is "true".
 
+### VFS Disk Options
+
+This flag allows you to manually set the statistics about the filing system.
+It can be useful when those statistics cannot be read correctly automatically.
+
+    --vfs-disk-space-total-size    Manually set the total disk space size (example: 256G, default: -1)
+
 ### Alternate report of used bytes
 
 Some backends, most notably S3, do not report the amount of bytes used.

vfs/vfs.go

@@ -604,6 +604,7 @@ func (vfs *VFS) Statfs() (total, used, free int64) {
 			return
 		}
 	}
+
 	if u := vfs.usage; u != nil {
 		if u.Total != nil {
 			total = *u.Total
@@ -615,6 +616,11 @@ func (vfs *VFS) Statfs() (total, used, free int64) {
 			used = *u.Used
 		}
 	}
+
+	if int64(vfs.Opt.DiskSpaceTotalSize) >= 0 {
+		total = int64(vfs.Opt.DiskSpaceTotalSize)
+	}
+
 	total, used, free = fillInMissingSizes(total, used, free, unknownFreeBytes)
 	return
 }

vfs/vfscommon/options.go

@@ -34,6 +34,7 @@ type Options struct {
 	ReadAhead          fs.SizeSuffix // bytes to read ahead in cache mode "full"
 	UsedIsSize         bool          // if true, use the `rclone size` algorithm for Used size
 	FastFingerprint    bool          // if set use fast fingerprints
+	DiskSpaceTotalSize fs.SizeSuffix
 }
 
 // DefaultOpt is the default values uses for Opt
@@ -61,6 +62,7 @@ var DefaultOpt = Options{
 	WriteBack:          5 * time.Second,
 	ReadAhead:          0 * fs.Mebi,
 	UsedIsSize:         false,
+	DiskSpaceTotalSize: -1,
 }
 
 // Init the options, making sure everything is withing range

vfs/vfsflags/vfsflags.go

@@ -39,5 +39,6 @@ func AddFlags(flagSet *pflag.FlagSet) {
 	flags.FVarP(flagSet, &Opt.ReadAhead, "vfs-read-ahead", "", "Extra read ahead over --buffer-size when using cache-mode full")
 	flags.BoolVarP(flagSet, &Opt.UsedIsSize, "vfs-used-is-size", "", Opt.UsedIsSize, "Use the `rclone size` algorithm for Used size")
 	flags.BoolVarP(flagSet, &Opt.FastFingerprint, "vfs-fast-fingerprint", "", Opt.FastFingerprint, "Use fast (less accurate) fingerprints for change detection")
+	flags.FVarP(flagSet, &Opt.DiskSpaceTotalSize, "vfs-disk-space-total-size", "", "Specify the total space of disk")
 	platformFlags(flagSet)
 }