unix: support Readv, Preadv, Writev and Pwritev for darwin

Darwin, starting with Big Sur, supports vectorized IO.

Fixes golang/go#64710

Change-Id: Ic3a3c51009eab24f70665d8d3a145b328a7713c6
Reviewed-on: https://go-review.googlesource.com/c/sys/+/548795
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

unix/syscall_darwin.go

@@ -602,7 +602,150 @@ func Connectx(fd int, srcIf uint32, srcAddr, dstAddr Sockaddr, associd SaeAssocI
 	return
 }
 
-//sys	connectx(fd int, endpoints *SaEndpoints, associd SaeAssocID, flags uint32, iov []Iovec, n *uintptr, connid *SaeConnID) (err error)
+// sys	connectx(fd int, endpoints *SaEndpoints, associd SaeAssocID, flags uint32, iov []Iovec, n *uintptr, connid *SaeConnID) (err error)
+const minIovec = 8
+
+func Readv(fd int, iovs [][]byte) (n int, err error) {
+	if !darwinKernelVersionMin(11, 0, 0) {
+		return 0, ENOSYS
+	}
+
+	iovecs := make([]Iovec, 0, minIovec)
+	iovecs = appendBytes(iovecs, iovs)
+	n, err = readv(fd, iovecs)
+	readvRacedetect(iovecs, n, err)
+	return n, err
+}
+
+func Preadv(fd int, iovs [][]byte, offset int64) (n int, err error) {
+	if !darwinKernelVersionMin(11, 0, 0) {
+		return 0, ENOSYS
+	}
+	iovecs := make([]Iovec, 0, minIovec)
+	iovecs = appendBytes(iovecs, iovs)
+	n, err = preadv(fd, iovecs, offset)
+	readvRacedetect(iovecs, n, err)
+	return n, err
+}
+
+func Writev(fd int, iovs [][]byte) (n int, err error) {
+	if !darwinKernelVersionMin(11, 0, 0) {
+		return 0, ENOSYS
+	}
+
+	iovecs := make([]Iovec, 0, minIovec)
+	iovecs = appendBytes(iovecs, iovs)
+	if raceenabled {
+		raceReleaseMerge(unsafe.Pointer(&ioSync))
+	}
+	n, err = writev(fd, iovecs)
+	writevRacedetect(iovecs, n)
+	return n, err
+}
+
+func Pwritev(fd int, iovs [][]byte, offset int64) (n int, err error) {
+	if !darwinKernelVersionMin(11, 0, 0) {
+		return 0, ENOSYS
+	}
+
+	iovecs := make([]Iovec, 0, minIovec)
+	iovecs = appendBytes(iovecs, iovs)
+	if raceenabled {
+		raceReleaseMerge(unsafe.Pointer(&ioSync))
+	}
+	n, err = pwritev(fd, iovecs, offset)
+	writevRacedetect(iovecs, n)
+	return n, err
+}
+
+func appendBytes(vecs []Iovec, bs [][]byte) []Iovec {
+	for _, b := range bs {
+		var v Iovec
+		v.SetLen(len(b))
+		if len(b) > 0 {
+			v.Base = &b[0]
+		} else {
+			v.Base = (*byte)(unsafe.Pointer(&_zero))
+		}
+		vecs = append(vecs, v)
+	}
+	return vecs
+}
+
+func writevRacedetect(iovecs []Iovec, n int) {
+	if !raceenabled {
+		return
+	}
+	for i := 0; n > 0 && i < len(iovecs); i++ {
+		m := int(iovecs[i].Len)
+		if m > n {
+			m = n
+		}
+		n -= m
+		if m > 0 {
+			raceReadRange(unsafe.Pointer(iovecs[i].Base), m)
+		}
+	}
+}
+
+func readvRacedetect(iovecs []Iovec, n int, err error) {
+	if !raceenabled {
+		return
+	}
+	for i := 0; n > 0 && i < len(iovecs); i++ {
+		m := int(iovecs[i].Len)
+		if m > n {
+			m = n
+		}
+		n -= m
+		if m > 0 {
+			raceWriteRange(unsafe.Pointer(iovecs[i].Base), m)
+		}
+	}
+	if err == nil {
+		raceAcquire(unsafe.Pointer(&ioSync))
+	}
+}
+
+func darwinMajorMinPatch() (maj, min, patch int, err error) {
+	var un Utsname
+	err = Uname(&un)
+	if err != nil {
+		return
+	}
+
+	var mmp [3]int
+	c := 0
+Loop:
+	for _, b := range un.Release[:] {
+		switch {
+		case b >= '0' && b <= '9':
+			mmp[c] = 10*mmp[c] + int(b-'0')
+		case b == '.':
+			c++
+			if c > 2 {
+				return 0, 0, 0, ENOTSUP
+			}
+		case b == 0:
+			break Loop
+		default:
+			return 0, 0, 0, ENOTSUP
+		}
+	}
+	if c != 2 {
+		return 0, 0, 0, ENOTSUP
+	}
+	return mmp[0], mmp[1], mmp[2], nil
+}
+
+func darwinKernelVersionMin(maj, min, patch int) bool {
+	actualMaj, actualMin, actualPatch, err := darwinMajorMinPatch()
+	if err != nil {
+		return false
+	}
+	return actualMaj > maj || actualMaj == maj && (actualMin > min || actualMin == min && actualPatch >= patch)
+}
+
 //sys	sendfile(infd int, outfd int, offset int64, len *int64, hdtr unsafe.Pointer, flags int) (err error)
 
 //sys	shmat(id int, addr uintptr, flag int) (ret uintptr, err error)
@@ -705,3 +848,7 @@ func Connectx(fd int, srcIf uint32, srcAddr, dstAddr Sockaddr, associd SaeAssocI
 //sys	write(fd int, p []byte) (n int, err error)
 //sys	mmap(addr uintptr, length uintptr, prot int, flag int, fd int, pos int64) (ret uintptr, err error)
 //sys	munmap(addr uintptr, length uintptr) (err error)
+//sys	readv(fd int, iovecs []Iovec) (n int, err error)
+//sys	preadv(fd int, iovecs []Iovec, offset int64) (n int, err error)
+//sys	writev(fd int, iovecs []Iovec) (n int, err error)
+//sys	pwritev(fd int, iovecs []Iovec, offset int64) (n int, err error)