Return EPERM for mknod

This more directly matches what Linux does with unsupported
nodes.

PiperOrigin-RevId: 248780425
Change-Id: I17f3dd0b244f6dc4eb00e2e42344851b8367fbec

pkg/sentry/fs/gofer/path.go

@@ -281,9 +281,9 @@ func (i *inodeOperations) Bind(ctx context.Context, dir *fs.Inode, name string,
 }
 
 // CreateFifo implements fs.InodeOperations.CreateFifo. Gofer nodes do not support the
-// creation of fifos and always returns EOPNOTSUPP.
+// creation of fifos and always returns EPERM.
 func (*inodeOperations) CreateFifo(context.Context, *fs.Inode, string, fs.FilePermissions) error {
-	return syscall.EOPNOTSUPP
+	return syscall.EPERM
 }
 
 // Remove implements InodeOperations.Remove.

pkg/sentry/fs/host/inode.go

@@ -287,7 +287,7 @@ func (*inodeOperations) CreateHardLink(context.Context, *fs.Inode, *fs.Inode, st
 
 // CreateFifo implements fs.InodeOperations.CreateFifo.
 func (*inodeOperations) CreateFifo(context.Context, *fs.Inode, string, fs.FilePermissions) error {
-	return syserror.EOPNOTSUPP
+	return syserror.EPERM
 }
 
 // Remove implements fs.InodeOperations.Remove.

runsc/fsgofer/fsgofer.go

@@ -860,7 +860,10 @@ func (l *localFile) Link(target p9.File, newName string) error {
 //
 // Not implemented.
 func (*localFile) Mknod(_ string, _ p9.FileMode, _ uint32, _ uint32, _ p9.UID, _ p9.GID) (p9.QID, error) {
-	return p9.QID{}, syscall.ENOSYS
+	// From mknod(2) man page:
+	// "EPERM: [...] if the filesystem containing pathname does not support
+	// the type of node requested."
+	return p9.QID{}, syscall.EPERM
 }
 
 // UnlinkAt implements p9.File.