From 147f97d1f78aa473416ed2cae9ef6a9c99fd8065 Mon Sep 17 00:00:00 2001
From: Nick Craig-Wood <nick@craig-wood.com>
Date: Fri, 15 May 2020 11:23:16 +0100
Subject: [PATCH] sync: allow --max-backlog to be -ve meaning as large as
 possible

---
 docs/content/docs.md | 3 +++
 fs/sync/pipe.go      | 4 ++++
 2 files changed, 7 insertions(+)

diff --git a/docs/content/docs.md b/docs/content/docs.md
index f9cbd6ff1..8585fff74 100644
--- a/docs/content/docs.md
+++ b/docs/content/docs.md
@@ -745,6 +745,9 @@ time and make `--order-by` work more accurately.
 Setting this small will make rclone more synchronous to the listings
 of the remote which may be desirable.
 
+Setting this to a negative number will make the backlog as large as
+possible.
+
 ### --max-delete=N ###
 
 This tells rclone not to delete more than N files.  If that limit is
diff --git a/fs/sync/pipe.go b/fs/sync/pipe.go
index 08b40c740..d618ce23b 100644
--- a/fs/sync/pipe.go
+++ b/fs/sync/pipe.go
@@ -2,6 +2,7 @@ package sync
 
 import (
 	"context"
+	"math/bits"
 	"strconv"
 	"strings"
 	"sync"
@@ -30,6 +31,9 @@ type pipe struct {
 }
 
 func newPipe(orderBy string, stats func(items int, totalSize int64), maxBacklog int) (*pipe, error) {
+	if maxBacklog < 0 {
+		maxBacklog = (1 << (bits.UintSize - 1)) - 1 // largest posititive int
+	}
 	less, fraction, err := newLess(orderBy)
 	if err != nil {
 		return nil, fserrors.FatalError(err)