unix: add readv/writev for illumos

iovec read/writes (readv, writev, preadv, pwritev) are present on
illumos, but they weren't added to the package. This commit adds
those missing features.

Updates golang/go#36201

Change-Id: Iecf2bab7ef846f5ca5d693e833491d819618c15d
GitHub-Last-Rev: 81a479f4c5f851f81e748cef6eb529c3f89cd1e1
GitHub-Pull-Request: golang/sys#64
Reviewed-on: https://go-review.googlesource.com/c/sys/+/224238
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

unix/syscall_illumos.go

@@ -0,0 +1,57 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// illumos system calls not present on Solaris.
+
+// +build amd64,illumos
+
+package unix
+
+import "unsafe"
+
+func bytes2iovec(bs [][]byte) []Iovec {
+	iovecs := make([]Iovec, len(bs))
+	for i, b := range bs {
+		iovecs[i].SetLen(len(b))
+		if len(b) > 0 {
+			// somehow Iovec.Base on illumos is (*int8), not (*byte)
+			iovecs[i].Base = (*int8)(unsafe.Pointer(&b[0]))
+		} else {
+			iovecs[i].Base = (*int8)(unsafe.Pointer(&_zero))
+		}
+	}
+	return iovecs
+}
+
+//sys   readv(fd int, iovs []Iovec) (n int, err error)
+
+func Readv(fd int, iovs [][]byte) (n int, err error) {
+	iovecs := bytes2iovec(iovs)
+	n, err = readv(fd, iovecs)
+	return n, err
+}
+
+//sys   preadv(fd int, iovs []Iovec, off int64) (n int, err error)
+
+func Preadv(fd int, iovs [][]byte, off int64) (n int, err error) {
+	iovecs := bytes2iovec(iovs)
+	n, err = preadv(fd, iovecs, off)
+	return n, err
+}
+
+//sys   writev(fd int, iovs []Iovec) (n int, err error)
+
+func Writev(fd int, iovs [][]byte) (n int, err error) {
+	iovecs := bytes2iovec(iovs)
+	n, err = writev(fd, iovecs)
+	return n, err
+}
+
+//sys   pwritev(fd int, iovs []Iovec, off int64) (n int, err error)
+
+func Pwritev(fd int, iovs [][]byte, off int64) (n int, err error) {
+	iovecs := bytes2iovec(iovs)
+	n, err = pwritev(fd, iovecs, off)
+	return n, err
+}