//sysnb exit(res int) (err error)
//sys   ptrace(request int, pid int, addr uintptr, data uintptr) (err error)
//sysnb getentropy(p []byte) (err error)
//sys   fstatat(fd int, path string, stat *Stat_t, flags int) (err error)
//sys   unlinkat(fd int, path string, flags int) (err error)

	if pfd == nil || !pfd.IsStream || !isUnixOrTCP(string(network)) {
		return
	}

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

	rerr := sc.Read(func(fd uintptr) (done bool) {
		written, err, handled = poll.SendFile(pfd, int(fd), 1<<63-1)
		return true
	})

	if err == nil {
		err = rerr
	}

	return written, handled, wrapSyscallError("sendfile", err)
}

	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

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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
	}

		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]

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00000220  71 15 fd 16 5b aa 01 c2  7b e3 c2 84 01 c0 f6 04  |q...[...{.......|
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00000250  dd 56 bc 66 17 03 03 00  35 9f 7e 2e 02 66 bb ac  |.V.f....5.~..f..|

00000140  5e dd 95 5a ba e4 5a 68  64 a6 44 f5 a2 3a d6 30  |^..Z..Zhd.D..:.0|
00000150  7e b1 27 b1 79 44 ef 79  95 51 75 02 24 2c ea ab  |~.'.yD.y.Qu.$,..|
00000160  d5 e1 fd aa 81 55 89 cf  bc 9c 11 2b 0b 4a 99 9f  |.....U.....+.J..|
00000170  50 93 68 a1 c8 79 3d d8  aa d8 54 e3 d5 1a 97 90  |P.h..y=...T.....|
00000180  33 87 a9 70 1d 9d ba 78  d0 87 8a 98 6f 1b 1e b0  |3..p...x....o...|

000000d0  ec b1 19 dd 68 b5 bd c4  bb ba 63 9a e4 c9 24 af  |....h.....c...$.|
000000e0  88 13 65 11 bf ea d9 07  e9 46 fd 5b 60 ce 57 46  |..e......F.[`.WF|
000000f0  8b a9 bd c6 58 1a 3b bd  5e fb 0f 46 ec fc 8b 2c  |....X.;.^..F...,|
00000100  ea a7 19 06 6a e5 6f 10  7a 27 04 6b aa a4 2c f4  |....j.o.z'.k..,.|
00000110  ef 3b e8 8a 51 88 fd e0  ae 33 b1 4c b3 04 5e 91  |.;..Q....3.L..^.|