if !ok {
		return 0, nil, false
	}

	sc, err := f.SyscallConn()
	if err != nil {
		return 0, nil, false
	}

	var werr error
	err = sc.Read(func(fd uintptr) bool {
		written, werr, handled = poll.SendFile(&c.pfd, int(fd), remain)
		return true
	})
	if err == nil {
		err = werr
	}

	if lr != nil {
		lr.N = remain - written
	}
	return written, wrapSyscallError("sendfile", err), handled

000000d0  52 c7 c2 84 cb 48 81 a3  da bd a1 50 5c ec 5c a7  |R....H.....P\.\.|
000000e0  10 01 58 cc 03 c3 53 04  03 69 80 f4 ad 4d ce 72  |..X...S..i...M.r|
000000f0  26 4e 6c c7 2c 31 69 2b  fd 97 67 5e 7d e0 05 b3  |&Nl.,1i+..g^}...|
00000100  f4 40 64 a1 bd a3 fd a8  f9 7b 18 82 89 8f 25 f9  |.@d......{....%.|
00000110  ca ca c4 8f e4 90 7b 26  7a d5 b2 1e fa 05 db ad  |......{&z.......|

000000d0  02 03 01 00 33 00 47 00  45 00 17 00 41 04 1e 18  |....3.G.E...A...|
000000e0  37 ef 0d 19 51 88 35 75  71 b5 e5 54 5b 12 2e 8f  |7...Q.5uq..T[...|
000000f0  09 67 fd a7 24 20 3e b2  56 1c ce 97 28 5e f8 2b  |.g..$ >.V...(^.+|
00000100  2d 4f 9e f1 07 9f 6c 4b  5b 83 56 e2 32 42 e9 58  |-O....lK[.V.2B.X|
00000110  b6 d7 49 a6 b5 68 1a 41  03 56 6b dc 5a 89        |..I..h.A.Vk.Z.|

package poll

import "syscall"

// maxSendfileSize is the largest chunk size we ask the kernel to copy
// at a time.
const maxSendfileSize int = 4 << 20

// SendFile wraps the sendfile system call.
func SendFile(dstFD *FD, src int, pos, remain int64) (written int64, err error, handled bool) {
	defer func() {
		TestHookDidSendFile(dstFD, src, written, err, handled)
	}()
	if err := dstFD.writeLock(); err != nil {
		return 0, err, false
	}

		return false
	}
	return true
}

func GetFd(f fs.File) (uintptr, error) {
	if fdable, ok := f.(interface{ Fd() uintptr }); ok {
		return fdable.Fd(), nil
	}

	return 0, fmt.Errorf("unable to get fd")
}

/// mostly copy pasted from spire below:

// regexes listed here have to exclusively match a cgroup path

		importpaths[pd.PackagePath()] = struct{}{}
		var fd coverage.FuncDesc
		nf := pd.NumFuncs()
		for fnIdx := uint32(0); fnIdx < nf; fnIdx++ {
			if err := pd.ReadFunc(fnIdx, &fd); err != nil {
				return fmt.Errorf("reading meta-data file %s: %v",
					p.MetaFile, err)
			}
			key := pkfunc{pk: pkIdx, fcn: fnIdx}
			counters, haveCounters := pmm[key]
			for i := 0; i < len(fd.Units); i++ {
				u := fd.Units[i]

000002e0  cf 9b ae c3 e0 2f d4 80  f8 be 4f 9d 87 53 fd 53  |...../....O..S.S|
000002f0  b6 a2 cf b9 8e 56 85 39  16 03 03 00 bc 63 23 39  |.....V.9.....c#9|
00000300  de e9 93 fb f0 9b 64 b6  5e 7c a0 47 f6 b3 99 16  |......d.^|.G....|
00000310  1c 68 f3 f6 3f bd a0 fc  80 09 6d 95 9a 17 65 e0  |.h..?.....m...e.|
00000320  c2 ee fa cf fd af d8 05  5c 17 f1 1f a3 1c f2 47  |........\......G|

			runtime.LockOSThread()
			Fixwd()
			return true
		}
	}
	return false
}

// goroutine-specific getwd
func getwd() (wd string, err error) {
	fd, err := open(".", O_RDONLY)
	if err != nil {
		return "", err
	}
	defer Close(fd)
	return Fd2path(fd)
}

func Getwd() (wd string, err error) {
	wdmu.Lock()
	defer wdmu.Unlock()

	if wdSet {
		return wdStr, nil
	}
	wd, err = getwd()

		t.Errorf("texta value = %q, want %q", g, e)
	}
	fd := testFile(t, f.File["filea"][0], "filea.txt", fileaContents)
	if _, ok := fd.(*os.File); ok {
		t.Error("file is *os.File, should not be")
	}
	fd.Close()
	fd = testFile(t, f.File["fileb"][0], "fileb.txt", filebContents)
	if _, ok := fd.(*os.File); !ok {
		t.Errorf("file has unexpected underlying type %T", fd)
	}
	fd.Close()
}

00000210  10 79 08 d4 ce 9e e2 cb  0b 86 a4 b1 80 e4 1b ac  |.y..............|
00000220  71 15 fd 16 5b aa 01 c2  7b e3 c2 84 01 c0 f6 04  |q...[...{.......|
00000230  a7 31 2b ec f2 50 bf 5a  07 6f b8 03 9f d2 c6 ad  |.1+..P.Z.o......|
00000240  73 18 81 f5 fd 9a 5a b2  bc 9f 85 94 9f f6 da da  |s.....Z.........|
00000250  dd 56 bc 66 17 03 03 00  35 9f 7e 2e 02 66 bb ac  |.V.f....5.~..f..|