From a4587d50708a73b65089c87e17523fac92d0249a Mon Sep 17 00:00:00 2001
From: Luke Shumaker <lukeshu@beefcake.parabola.nu>
Date: Sat, 26 May 2018 00:51:34 -0400
Subject: cow-dedupe: Don't pass too many arguments to cow-dedupe-range at once

---
 go/src/cow-dedupe/dedupe.go | 42 +++++++++++++++++++++++++++++++-----------
 1 file changed, 31 insertions(+), 11 deletions(-)

diff --git a/go/src/cow-dedupe/dedupe.go b/go/src/cow-dedupe/dedupe.go
index dc37491..bc543f1 100644
--- a/go/src/cow-dedupe/dedupe.go
+++ b/go/src/cow-dedupe/dedupe.go
@@ -19,6 +19,7 @@ import (
 import "C"
 
 var arg_max = int(C.sysconf(C._SC_ARG_MAX))
+var open_max = int(C.sysconf(C._SC_OPEN_MAX))
 
 func errhandle(err error) {
 	if err != nil {
@@ -139,21 +140,40 @@ func pruneSingles(key2vals map[string][]string) {
 
 func dedupe(srcFile string, dupFiles []string) error {
 	stat, err := os.Stat(srcFile)
-	errhandle(err)
-	args := []string{
+	if err != nil {
+		return err
+	}
+	baseArgs := []string{
 		"-r", "--", strconv.FormatInt(stat.Size(), 10),
 		srcFile, "0",
 	}
-	for _, dupFile := range dupFiles {
-		args = append(args, dupFile, "0")
-	}
 
-	cmd := exec.Command("./cow-dedupe-range", args...)
-	cmd.Stdout = os.Stdout
-	cmd.Stderr = os.Stderr
-	//fmt.Println("#", checksum)
-	//fmt.Println(cmd.Args)
-	return cmd.Run()
+	dupFilesTodo := dupFiles
+	for len(dupFilesTodo) > 0 {
+		dupFilesDoing := dupFilesTodo
+		arg_len := 0
+		for i := range dupFilesDoing {
+			arg_len += len(dupFilesDoing[i]) + 3
+			if arg_len > arg_max/2 || (i+15) > open_max {
+				dupFilesDoing = dupFilesDoing[:i-1]
+				break
+			}
+		}
+		dupFilesTodo = dupFilesTodo[len(dupFilesDoing):]
+
+		args := baseArgs
+		for _, dupFile := range dupFilesDoing {
+			args = append(args, dupFile, "0")
+		}
+
+		cmd := exec.Command("./cow-dedupe-range", args...)
+		cmd.Stdout = os.Stdout
+		cmd.Stderr = os.Stderr
+		if _err := cmd.Run(); _err != nil {
+			err = _err
+		}
+	}
+	return err
 }
 
 // [ 0s ] size-set[n/d]->c :: sha256-set[t+n/d]->c :: (summed=n deduped=n) :: verb[m/n]
-- 
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