From 0f82812b9a514dd2e23ea7ec509f40a9988577f4 Mon Sep 17 00:00:00 2001
From: Ivan Shapovalov <intelfx@intelfx.name>
Date: Thu, 5 Dec 2024 18:12:33 +0400
Subject: [PATCH] WIP: remember and log last non-fatal clone error

---
 internal/fs/file.go           | 10 +++++++---
 internal/restorer/restorer.go |  7 ++++++-
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/internal/fs/file.go b/internal/fs/file.go
index 78db7c696..26b33fb95 100644
--- a/internal/fs/file.go
+++ b/internal/fs/file.go
@@ -151,16 +151,20 @@ func doClone(srcName, destName string, method cloneMethod) (cloned bool, err err
 
 // Clone performs a local possibly accelerated copy of srcName to destName.
 // The cloned flag reports whether an accelerated copy (reflink) was performed.
-func Clone(srcName, destName string) (cloned bool, err error) {
+// The cloneErr value specifies the last non-fatal error during attempted
+// accelerated copy.
+func Clone(srcName, destName string) (cloned bool, err error, cloneErr error) {
 	for _, fn := range cloneMethods {
 		cloned, err = doClone(srcName, destName, fn)
 		// if a particular method is not supported, or we hit the cross-device limitation,
 		// "eat" the error and go to the next method or the fallback
 		if errors.Is(err, unix.EXDEV) || errors.Is(err, unix.ENOTSUP) {
+			cloneErr = err
 			continue
 		}
-		return cloned, err
+		return cloned, err, cloneErr
 	}
 
-	return doClone(srcName, destName, doCloneCopy)
+	cloned, err = doClone(srcName, destName, doCloneCopy)
+	return cloned, err, cloneErr
 }
diff --git a/internal/restorer/restorer.go b/internal/restorer/restorer.go
index 56ec29c21..0312a64dc 100644
--- a/internal/restorer/restorer.go
+++ b/internal/restorer/restorer.go
@@ -318,18 +318,23 @@ func (res *Restorer) restoreHardlinkAt(node *restic.Node, target, path, location
 
 func (res *Restorer) restoreReflink(node *restic.Node, target, path, location string) error {
 	cloned := true
+	var cloneErr error
 	if !res.opts.DryRun {
 		var err error
 		if err = fs.Remove(path); err != nil && !errors.Is(err, os.ErrNotExist) {
 			return errors.Wrap(err, "RemoveNode")
 		}
-		cloned, err = fs.Clone(target, path)
+		cloned, err, cloneErr = fs.Clone(target, path)
 		if err != nil {
 			return errors.WithStack(err)
 		}
 	}
 
 	res.opts.Progress.AddClonedFile(location, node.Size, cloned)
+	if !cloned {
+		fmt.Fprintf(os.Stderr, "warning: could not reflink %v to %v: %v\n", target, path, cloneErr)
+	}
+
 	// reflinked files *do* have separate metadata
 	return res.restoreNodeMetadataTo(node, path, location)
 }