Use string type for extended attribute values, instead of []byte.

Strings are a better fit for this usage because they are immutable in Go, and
can contain arbitrary bytes. It also allows us to avoid casting bytes to string
(and the associated allocation) in the hot path when checking for overlay
whiteouts.

PiperOrigin-RevId: 242208856
Change-Id: I7699ae6302492eca71787dd0b72e0a5a217a3db2

pkg/sentry/fs/fsutil/inode.go

@@ -197,25 +197,25 @@ func (i *InodeSimpleAttributes) NotifyStatusChange(ctx context.Context) {
 type InodeSimpleExtendedAttributes struct {
 	// mu protects xattrs.
 	mu     sync.RWMutex `state:"nosave"`
-	xattrs map[string][]byte
+	xattrs map[string]string
 }
 
 // Getxattr implements fs.InodeOperations.Getxattr.
-func (i *InodeSimpleExtendedAttributes) Getxattr(_ *fs.Inode, name string) ([]byte, error) {
+func (i *InodeSimpleExtendedAttributes) Getxattr(_ *fs.Inode, name string) (string, error) {
 	i.mu.RLock()
 	value, ok := i.xattrs[name]
 	i.mu.RUnlock()
 	if !ok {
-		return nil, syserror.ENOATTR
+		return "", syserror.ENOATTR
 	}
 	return value, nil
 }
 
 // Setxattr implements fs.InodeOperations.Setxattr.
-func (i *InodeSimpleExtendedAttributes) Setxattr(_ *fs.Inode, name string, value []byte) error {
+func (i *InodeSimpleExtendedAttributes) Setxattr(_ *fs.Inode, name, value string) error {
 	i.mu.Lock()
 	if i.xattrs == nil {
-		i.xattrs = make(map[string][]byte)
+		i.xattrs = make(map[string]string)
 	}
 	i.xattrs[name] = value
 	i.mu.Unlock()
@@ -424,12 +424,12 @@ func (InodeNotSymlink) Getlink(context.Context, *fs.Inode) (*fs.Dirent, error) {
 type InodeNoExtendedAttributes struct{}
 
 // Getxattr implements fs.InodeOperations.Getxattr.
-func (InodeNoExtendedAttributes) Getxattr(*fs.Inode, string) ([]byte, error) {
-	return nil, syserror.EOPNOTSUPP
+func (InodeNoExtendedAttributes) Getxattr(*fs.Inode, string) (string, error) {
+	return "", syserror.EOPNOTSUPP
 }
 
 // Setxattr implements fs.InodeOperations.Setxattr.
-func (InodeNoExtendedAttributes) Setxattr(*fs.Inode, string, []byte) error {
+func (InodeNoExtendedAttributes) Setxattr(*fs.Inode, string, string) error {
 	return syserror.EOPNOTSUPP
 }
 

pkg/sentry/fs/inode.go

@@ -253,7 +253,7 @@ func (i *Inode) UnstableAttr(ctx context.Context) (UnstableAttr, error) {
 }
 
 // Getxattr calls i.InodeOperations.Getxattr with i as the Inode.
-func (i *Inode) Getxattr(name string) ([]byte, error) {
+func (i *Inode) Getxattr(name string) (string, error) {
 	if i.overlay != nil {
 		return overlayGetxattr(i.overlay, name)
 	}

pkg/sentry/fs/inode_operations.go

@@ -174,11 +174,11 @@ type InodeOperations interface {
 	// do not support extended attributes return EOPNOTSUPP. Inodes that
 	// support extended attributes but don't have a value at name return
 	// ENODATA.
-	Getxattr(inode *Inode, name string) ([]byte, error)
+	Getxattr(inode *Inode, name string) (string, error)
 
 	// Setxattr sets the value of extended attribute name. Inodes that
 	// do not support extended attributes return EOPNOTSUPP.
-	Setxattr(inode *Inode, name string, value []byte) error
+	Setxattr(inode *Inode, name, value string) error
 
 	// Listxattr returns the set of all extended attributes names that
 	// have values. Inodes that do not support extended attributes return

pkg/sentry/fs/inode_overlay.go

@@ -25,12 +25,12 @@ import (
 )
 
 func overlayHasWhiteout(parent *Inode, name string) bool {
-	buf, err := parent.Getxattr(XattrOverlayWhiteout(name))
-	return err == nil && string(buf) == "y"
+	s, err := parent.Getxattr(XattrOverlayWhiteout(name))
+	return err == nil && s == "y"
 }
 
 func overlayCreateWhiteout(parent *Inode, name string) error {
-	return parent.InodeOperations.Setxattr(parent, XattrOverlayWhiteout(name), []byte("y"))
+	return parent.InodeOperations.Setxattr(parent, XattrOverlayWhiteout(name), "y")
 }
 
 func overlayWriteOut(ctx context.Context, o *overlayEntry) error {
@@ -491,28 +491,28 @@ func overlayUnstableAttr(ctx context.Context, o *overlayEntry) (UnstableAttr, er
 	return attr, err
 }
 
-func overlayGetxattr(o *overlayEntry, name string) ([]byte, error) {
+func overlayGetxattr(o *overlayEntry, name string) (string, error) {
 	// Hot path. This is how the overlay checks for whiteout files.
 	// Avoid defers.
 	var (
-		b   []byte
+		s   string
 		err error
 	)
 
 	// Don't forward the value of the extended attribute if it would
 	// unexpectedly change the behavior of a wrapping overlay layer.
 	if strings.HasPrefix(XattrOverlayPrefix, name) {
-		return nil, syserror.ENODATA
+		return "", syserror.ENODATA
 	}
 
 	o.copyMu.RLock()
 	if o.upper != nil {
-		b, err = o.upper.Getxattr(name)
+		s, err = o.upper.Getxattr(name)
 	} else {
-		b, err = o.lower.Getxattr(name)
+		s, err = o.lower.Getxattr(name)
 	}
 	o.copyMu.RUnlock()
-	return b, err
+	return s, err
 }
 
 func overlayListxattr(o *overlayEntry) (map[string]struct{}, error) {

pkg/sentry/fs/inode_overlay_test.go

@@ -383,13 +383,13 @@ type dir struct {
 }
 
 // Getxattr implements InodeOperations.Getxattr.
-func (d *dir) Getxattr(inode *fs.Inode, name string) ([]byte, error) {
+func (d *dir) Getxattr(inode *fs.Inode, name string) (string, error) {
 	for _, n := range d.negative {
 		if name == fs.XattrOverlayWhiteout(n) {
-			return []byte("y"), nil
+			return "y", nil
 		}
 	}
-	return nil, syserror.ENOATTR
+	return "", syserror.ENOATTR
 }
 
 // GetFile implements InodeOperations.GetFile.

pkg/sentry/fs/tmpfs/tmpfs.go

@@ -150,12 +150,12 @@ func (d *Dir) CreateFifo(ctx context.Context, dir *fs.Inode, name string, perms
 }
 
 // Getxattr implements fs.InodeOperations.Getxattr.
-func (d *Dir) Getxattr(i *fs.Inode, name string) ([]byte, error) {
+func (d *Dir) Getxattr(i *fs.Inode, name string) (string, error) {
 	return d.ramfsDir.Getxattr(i, name)
 }
 
 // Setxattr implements fs.InodeOperations.Setxattr.
-func (d *Dir) Setxattr(i *fs.Inode, name string, value []byte) error {
+func (d *Dir) Setxattr(i *fs.Inode, name, value string) error {
 	return d.ramfsDir.Setxattr(i, name, value)
 }