Allow O_DIRECT with gofer.specialFileFD that represent regular files.

gofer.specialFileFD can sometimes represent regular files. O_DIRECT
is expected to be supported there.

PiperOrigin-RevId: 476408649

pkg/sentry/fsimpl/gofer/filesystem.go

@@ -1255,7 +1255,7 @@ func (d *dentry) openSocketByConnecting(ctx context.Context, opts *vfs.OpenOptio
 
 func (d *dentry) openSpecialFile(ctx context.Context, mnt *vfs.Mount, opts *vfs.OpenOptions) (*vfs.FileDescription, error) {
 	ats := vfs.AccessTypesForOpenFlags(opts)
-	if opts.Flags&linux.O_DIRECT != 0 {
+	if opts.Flags&linux.O_DIRECT != 0 && !d.isRegularFile() {
 		return nil, linuxerr.EINVAL
 	}
 	// We assume that the server silently inserts O_NONBLOCK in the open flags

pkg/sentry/fsimpl/gofer/special_file.go

@@ -108,8 +108,9 @@ func newSpecialFileFD(h handle, mnt *vfs.Mount, d *dentry, flags uint32) (*speci
 		}
 	}
 	if err := fd.vfsfd.Init(fd, flags, mnt, &d.vfsd, &vfs.FileDescriptionOptions{
-		DenyPRead:  !seekable,
-		DenyPWrite: !seekable,
+		AllowDirectIO: true,
+		DenyPRead:     !seekable,
+		DenyPWrite:    !seekable,
 	}); err != nil {
 		if haveQueue {
 			fdnotifier.RemoveFD(h.fd)