local: disable xattr support if the filesystems indicates it is not supported

Before this change, if rclone was run with `-M` on a filesystem
without xattr support, it would error out.

This patch makes rclone detect the not supported errors and disable
xattrs from then on. It prints one ERROR level message about this.

See: https://forum.rclone.org/t/metadata-update-local-s3/32277/7

backend/local/local.go

@@ -234,15 +234,16 @@ type Options struct {
 
 // Fs represents a local filesystem rooted at root
 type Fs struct {
-	name        string              // the name of the remote
-	root        string              // The root directory (OS path)
-	opt         Options             // parsed config options
-	features    *fs.Features        // optional features
-	dev         uint64              // device number of root node
-	precisionOk sync.Once           // Whether we need to read the precision
-	precision   time.Duration       // precision of local filesystem
-	warnedMu    sync.Mutex          // used for locking access to 'warned'.
-	warned      map[string]struct{} // whether we have warned about this string
+	name           string              // the name of the remote
+	root           string              // The root directory (OS path)
+	opt            Options             // parsed config options
+	features       *fs.Features        // optional features
+	dev            uint64              // device number of root node
+	precisionOk    sync.Once           // Whether we need to read the precision
+	precision      time.Duration       // precision of local filesystem
+	warnedMu       sync.Mutex          // used for locking access to 'warned'.
+	warned         map[string]struct{} // whether we have warned about this string
+	xattrSupported int32               // whether xattrs are supported (atomic access)
 
 	// do os.Lstat or os.Stat
 	lstat        func(name string) (os.FileInfo, error)
@@ -286,6 +287,9 @@ func NewFs(ctx context.Context, name, root string, m configmap.Mapper) (fs.Fs, e
 		dev:    devUnset,
 		lstat:  os.Lstat,
 	}
+	if xattrSupported {
+		f.xattrSupported = 1
+	}
 	f.root = cleanRootPath(root, f.opt.NoUNC, f.opt.Enc)
 	f.features = (&fs.Features{
 		CaseInsensitive:         f.caseInsensitive(),

backend/local/xattr.go

@@ -6,6 +6,8 @@ package local
 import (
 	"fmt"
 	"strings"
+	"sync/atomic"
+	"syscall"
 
 	"github.com/pkg/xattr"
 	"github.com/rclone/rclone/fs"
@@ -16,12 +18,30 @@ const (
 	xattrSupported = xattr.XATTR_SUPPORTED
 )
 
+// Check to see if the error supplied is a not supported error, and if
+// so, disable xattrs
+func (f *Fs) xattrIsNotSupported(err error) bool {
+	xattrErr, ok := err.(*xattr.Error)
+	if !ok {
+		return false
+	}
+	// Xattrs not supported can be ENOTSUP or ENOATTR or EINVAL (on Solaris)
+	if xattrErr.Err == syscall.EINVAL || xattrErr.Err == syscall.ENOTSUP || xattrErr.Err == xattr.ENOATTR {
+		// Show xattrs not supported
+		if atomic.CompareAndSwapInt32(&f.xattrSupported, 1, 0) {
+			fs.Errorf(f, "xattrs not supported - disabling: %v", err)
+		}
+		return true
+	}
+	return false
+}
+
 // getXattr returns the extended attributes for an object
 //
 // It doesn't return any attributes owned by this backend in
 // metadataKeys
 func (o *Object) getXattr() (metadata fs.Metadata, err error) {
-	if !xattrSupported {
+	if !xattrSupported || atomic.LoadInt32(&o.fs.xattrSupported) == 0 {
 		return nil, nil
 	}
 	var list []string
@@ -31,6 +51,9 @@ func (o *Object) getXattr() (metadata fs.Metadata, err error) {
 		list, err = xattr.LList(o.path)
 	}
 	if err != nil {
+		if o.fs.xattrIsNotSupported(err) {
+			return nil, nil
+		}
 		return nil, fmt.Errorf("failed to read xattr: %w", err)
 	}
 	if len(list) == 0 {
@@ -45,6 +68,9 @@ func (o *Object) getXattr() (metadata fs.Metadata, err error) {
 			v, err = xattr.LGet(o.path, k)
 		}
 		if err != nil {
+			if o.fs.xattrIsNotSupported(err) {
+				return nil, nil
+			}
 			return nil, fmt.Errorf("failed to read xattr key %q: %w", k, err)
 		}
 		k = strings.ToLower(k)
@@ -64,7 +90,7 @@ func (o *Object) getXattr() (metadata fs.Metadata, err error) {
 //
 // It doesn't set any attributes owned by this backend in metadataKeys
 func (o *Object) setXattr(metadata fs.Metadata) (err error) {
-	if !xattrSupported {
+	if !xattrSupported || atomic.LoadInt32(&o.fs.xattrSupported) == 0 {
 		return nil
 	}
 	for k, value := range metadata {
@@ -80,6 +106,9 @@ func (o *Object) setXattr(metadata fs.Metadata) (err error) {
 			err = xattr.LSet(o.path, k, v)
 		}
 		if err != nil {
+			if o.fs.xattrIsNotSupported(err) {
+				return nil
+			}
 			return fmt.Errorf("failed to set xattr key %q: %w", k, err)
 		}
 	}