vfs: add --vfs-read-wait and --vfs-write-wait flags

--vfs-read-wait duration    Time to wait for in-sequence read before seeking. (default 5ms)
    --vfs-write-wait duration   Time to wait for in-sequence write before giving error. (default 1s)

See: https://forum.rclone.org/t/constantly-high-iowait-add-log/14156

vfs/read.go

@@ -232,9 +232,10 @@ func (fh *ReadFileHandle) readAt(p []byte, off int64) (n int, err error) {
 	if gap := off - fh.offset; gap > 0 && gap < int64(8*maxBuf) {
 		// Set a background timer so we don't wait for long
 		// Waits here potentially affect all seeks so need to keep them short
-		// This time here was made by finding the smallest when mounting a local backend
-		// that didn't cause seeks.
-		const maxWait = 5 * time.Millisecond
+		// The default time here was made by finding the
+		// smallest when mounting a local backend that didn't
+		// cause seeks.
+		maxWait := fh.file.d.vfs.Opt.ReadWait
 		timeout := time.NewTimer(maxWait)
 		done := make(chan struct{})
 		abort := int32(0)

vfs/vfs.go

@@ -53,6 +53,8 @@ var DefaultOpt = Options{
 	ChunkSizeLimit:    -1,
 	CacheMaxSize:      -1,
 	CaseInsensitive:   runtime.GOOS == "windows" || runtime.GOOS == "darwin", // default to true on Windows and Mac, false otherwise
+	WriteWait:         1000 * time.Millisecond,
+	ReadWait:          5 * time.Millisecond,
 }
 
 // Node represents either a directory (*Dir) or a file (*File)
@@ -202,6 +204,8 @@ type Options struct {
 	CacheMaxSize      fs.SizeSuffix
 	CachePollInterval time.Duration
 	CaseInsensitive   bool
+	WriteWait         time.Duration // time to wait for in-sequence write
+	ReadWait          time.Duration // time to wait for in-sequence read
 }
 
 // New creates a new VFS and root directory.  If opt is nil, then

vfs/vfsflags/vfsflags.go

@@ -33,5 +33,7 @@ func AddFlags(flagSet *pflag.FlagSet) {
 	flags.FVarP(flagSet, DirPerms, "dir-perms", "", "Directory permissions")
 	flags.FVarP(flagSet, FilePerms, "file-perms", "", "File permissions")
 	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.")
 	platformFlags(flagSet)
 }

vfs/write.go

@@ -132,7 +132,8 @@ func (fh *WriteFileHandle) writeAt(p []byte, off int64) (n int, err error) {
 	}
 	if fh.offset != off {
 		// Set a background timer so we don't wait forever
-		timeout := time.NewTimer(10 * time.Second)
+		maxWait := fh.file.d.vfs.Opt.WriteWait
+		timeout := time.NewTimer(maxWait)
 		done := make(chan struct{})
 		abort := int32(0)
 		go func() {