From a8535aba58c3fe5056d35e5fd14d0400e757ca38 Mon Sep 17 00:00:00 2001
From: Michael Terry <mike@mterry.name>
Date: Fri, 4 Apr 2025 10:22:54 -0400
Subject: [PATCH] backend/local: ignore chmod "not supported" errors

---
 changelog/unreleased/issue-5342      | 7 +++++++
 internal/backend/local/local_unix.go | 9 ++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 changelog/unreleased/issue-5342

diff --git a/changelog/unreleased/issue-5342 b/changelog/unreleased/issue-5342
new file mode 100644
index 000000000..e9887fda2
--- /dev/null
+++ b/changelog/unreleased/issue-5342
@@ -0,0 +1,7 @@
+Bugfix: Ignore "chmod not supported" errors when writing files
+
+Restic 0.18.0 introduced a bug that caused "chmod xxx: operation not supported"
+errors to appear when writing to a local file repository that did not support
+chmod (like CIFS or WebDAV mounted via FUSE). Restic now ignores those errors.
+
+https://github.com/restic/restic/issues/5342
diff --git a/internal/backend/local/local_unix.go b/internal/backend/local/local_unix.go
index e52587456..b885ae1a3 100644
--- a/internal/backend/local/local_unix.go
+++ b/internal/backend/local/local_unix.go
@@ -43,5 +43,12 @@ func isMacENOTTY(err error) bool {
 
 // set file to readonly
 func setFileReadonly(f string, mode os.FileMode) error {
-	return os.Chmod(f, mode&^0222)
+	err := os.Chmod(f, mode&^0222)
+
+	// ignore the error if the FS does not support setting this mode (e.g. CIFS with gvfs on Linux)
+	if err != nil && errors.Is(err, errors.ErrUnsupported) {
+		return nil
+	}
+
+	return err
 }