xattr: added passing of a "flags" parameter

Pass the "flags" parameter to the lower layer syscall.
This makes Apple applications being able to successfully save data.

internal/fusefrontend/xattr.go

@@ -54,14 +54,12 @@ func (fs *FS) SetXAttr(path string, attr string, data []byte, flags int, context
 	if fs.isFiltered(path) {
 		return fuse.EPERM
 	}
-	if flags != 0 {
-		// Drop this once https://github.com/pkg/xattr/pull/26 is merged
-		return fuse.ENOSYS
-	}
 	if disallowedXAttrName(attr) {
 		return fuse.EPERM
 	}
 
+	flags = filterXattrSetFlags(flags)
+
 	cPath, err := fs.getBackingPath(path)
 	if err != nil {
 		return fuse.ToStatus(err)
@@ -69,7 +67,7 @@ func (fs *FS) SetXAttr(path string, attr string, data []byte, flags int, context
 	cAttr := fs.encryptXattrName(attr)
 	// xattr data is encrypted like a symlink target
 	cData64 := []byte(fs.encryptSymlinkTarget(string(data)))
-	return unpackXattrErr(xattr.Set(cPath, cAttr, cData64))
+	return unpackXattrErr(xattr.SetWithFlags(cPath, cAttr, cData64, flags))
 }
 
 // RemoveXAttr implements pathfs.Filesystem.

internal/fusefrontend/xattr_darwin.go

@@ -0,0 +1,15 @@
+// +build darwin
+
+// Package fusefrontend interfaces directly with the go-fuse library.
+package fusefrontend
+
+import "github.com/pkg/xattr"
+
+func disallowedXAttrName(attr string) bool {
+	return false
+}
+
+// On Darwin it is needed to unset XATTR_NOSECURITY 0x0008
+func filterXattrSetFlags(flags int) int {
+	return flags &^ xattr.XATTR_NOSECURITY
+}

internal/fusefrontend/xattr_linux.go

@@ -13,3 +13,7 @@ const xattrUserPrefix = "user."
 func disallowedXAttrName(attr string) bool {
 	return !strings.HasPrefix(attr, xattrUserPrefix)
 }
+
+func filterXattrSetFlags(flags int) int {
+	return flags
+}

internal/fusefrontend/xattr_notlinux.go

@@ -1,8 +0,0 @@
-// +build !linux
-
-// Package fusefrontend interfaces directly with the go-fuse library.
-package fusefrontend
-
-func disallowedXAttrName(attr string) bool {
-	return false
-}