internal/poll, internal/syscall/unix, net: enable writev on illumos

Illumos supports iovec read/write. Add the writev wrapper to
internal/syscall/unix and use it to implement internal/poll.writev for
net.(*netFD).writeBuffers.

Change-Id: Ie256c2f96aba8e61fb21991788789a049425f792
Reviewed-on: https://go-review.googlesource.com/c/go/+/254638
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Trust: Tobias Klauser <tobias.klauser@gmail.com>

1 files changed, 30 insertions, 0 deletions

diff --git a/src/internal/syscall/unix/writev_illumos.go b/src/internal/syscall/unix/writev_illumos.go
new file mode 100644
index 0000000000..eb7973d65b
--- /dev/null
+++ b/src/internal/syscall/unix/writev_illumos.go
@@ -0,0 +1,30 @@
+// Copyright 2020 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.
+
+// +build illumos
+
+package unix
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+//go:cgo_import_dynamic libc_writev writev "libc.so"
+
+//go:linkname procwritev libc_writev
+
+var procwritev uintptr
+
+func Writev(fd int, iovs []syscall.Iovec) (uintptr, error) {
+	var p *syscall.Iovec
+	if len(iovs) > 0 {
+		p = &iovs[0]
+	}
+	n, _, errno := syscall6(uintptr(unsafe.Pointer(&procwritev)), 3, uintptr(fd), uintptr(unsafe.Pointer(p)), uintptr(len(iovs)), 0, 0, 0)
+	if errno != 0 {
+		return 0, errno
+	}
+	return n, nil
+}