const n = this.writeSync(fd, buf);
				callback(null, n);
			},
			chmod(path, mode, callback) { callback(enosys()); },
			chown(path, uid, gid, callback) { callback(enosys()); },
			close(fd, callback) { callback(enosys()); },
			fchmod(fd, mode, callback) { callback(enosys()); },
			fchown(fd, uid, gid, callback) { callback(enosys()); },
			fstat(fd, callback) { callback(enosys()); },
			fsync(fd, callback) { callback(null); },

		{call: "Setreuid(1,0)", fn: func() error { return syscall.Setreuid(1, 0) }, filter: "Uid:", expect: "\t1\t0\t0\t0"},
		{call: "Setreuid(0,2)", fn: func() error { return syscall.Setreuid(0, 2) }, filter: "Uid:", expect: "\t0\t2\t2\t2"},
		{call: "Setreuid(0,0)", fn: func() error { return syscall.Setreuid(0, 0) }, filter: "Uid:", expect: "\t0\t0\t0\t0"},

		want *Header
		ok   bool
	}{{
		in: map[string]string{
			"path":  "a/b/c",
			"uid":   "1000",
			"mtime": "1350244992.023960108",
		},
		want: &Header{
			Name:    "a/b/c",
			Uid:     1000,
			ModTime: time.Unix(1350244992, 23960108),
			PAXRecords: map[string]string{
				"path":  "a/b/c",
				"uid":   "1000",
				"mtime": "1350244992.023960108",
			},
		},
		ok: true,
	}, {

	verifyString(h.Uname, len(ustar.userName()), "Uname", paxUname)
	verifyString(h.Gname, len(ustar.groupName()), "Gname", paxGname)
	verifyNumeric(h.Mode, len(v7.mode()), "Mode", paxNone)
	verifyNumeric(int64(h.Uid), len(v7.uid()), "Uid", paxUid)
	verifyNumeric(int64(h.Gid), len(v7.gid()), "Gid", paxGid)
	verifyNumeric(h.Size, len(v7.size()), "Size", paxSize)
	verifyNumeric(h.Devmajor, len(ustar.devMajor()), "Devmajor", paxNone)

			t.Errorf("i=%d: Name: got %v, want %v", i, got, want)
		}
		if got, want := h2.Size, v.h.Size; got != want {
			t.Errorf("i=%d: Size: got %v, want %v", i, got, want)
		}
		if got, want := h2.Uid, v.h.Uid; got != want {
			t.Errorf("i=%d: Uid: got %d, want %d", i, got, want)
		}
		if got, want := h2.Gid, v.h.Gid; got != want {
			t.Errorf("i=%d: Gid: got %d, want %d", i, got, want)
		}

				Size:     5,
				Mode:     0640,
				Uid:      73025,
				Gid:      5000,
				Uname:    "dsymonds",
				Gname:    "eng",
				ModTime:  time.Unix(1246508266, 0),
			}, nil},
			testWrite{"Kilts", 5, nil},

			testHeader{Header{
				Typeflag: TypeReg,
				Name:     "small2.txt",
				Size:     11,
				Mode:     0640,
				Uid:      73025,
				Uname:    "dsymonds",
				Gname:    "eng",

	sysStat = statUnix
}

// userMap and groupMap caches UID and GID lookups for performance reasons.
// The downside is that renaming uname or gname by the OS never takes effect.
var userMap, groupMap sync.Map // map[int]string

func statUnix(fi fs.FileInfo, h *Header, doNameLookups bool) error {
	sys, ok := fi.Sys().(*syscall.Stat_t)
	if !ok {
		return nil
	}
	h.Uid = int(sys.Uid)
	h.Gid = int(sys.Gid)
	if doNameLookups {

	hdr.Typeflag = v7.typeFlag()[0]
	hdr.Name = p.parseString(v7.name())
	hdr.Linkname = p.parseString(v7.linkName())
	hdr.Size = p.parseNumeric(v7.size())
	hdr.Mode = p.parseNumeric(v7.mode())
	hdr.Uid = int(p.parseNumeric(v7.uid()))
	hdr.Gid = int(p.parseNumeric(v7.gid()))
	hdr.ModTime = time.Unix(p.parseNumeric(v7.modTime()), 0)

	// Unpack format specific fields.
	if format > formatV7 {
		ustar := tr.blk.toUSTAR()

		modTime = time.Unix(0, 0)
	}

	v7 := tw.blk.toV7()
	v7.typeFlag()[0] = hdr.Typeflag
	fmtStr(v7.name(), hdr.Name)
	fmtStr(v7.linkName(), hdr.Linkname)
	fmtNum(v7.mode(), hdr.Mode)
	fmtNum(v7.uid(), int64(hdr.Uid))
	fmtNum(v7.gid(), int64(hdr.Gid))
	fmtNum(v7.size(), hdr.Size)
	fmtNum(v7.modTime(), modTime.Unix())

	ustar := tw.blk.toUSTAR()
	fmtStr(ustar.userName(), hdr.Uname)

pkg syscall (netbsd-arm64-cgo), type Credential struct, Groups []uint32
pkg syscall (netbsd-arm64-cgo), type Credential struct, NoSetGroups bool
pkg syscall (netbsd-arm64-cgo), type Credential struct, Uid uint32
pkg syscall (netbsd-arm64-cgo), type Dirent struct
pkg syscall (netbsd-arm64-cgo), type Dirent struct, Fileno uint64
pkg syscall (netbsd-arm64-cgo), type Dirent struct, Name [512]int8