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

The writev syscall is available since at least Solaris 11.3.

Reuse the existing illumos writev wrapper on solaris to implement
internal/poll.writev for net.(*netFD).writeBuffers.

Change-Id: I23adc3bb4637740c72bfb61bfa9697b432dfe3db
Reviewed-on: https://go-review.googlesource.com/c/go/+/427714
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

src/internal/poll/fd_writev_solaris.go

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build illumos
-
 package poll
 
 import (

src/internal/poll/iovec_solaris.go

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build illumos
-
 package poll
 
 import (

src/internal/poll/writev.go

@@ -2,12 +2,13 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build darwin || dragonfly || freebsd || illumos || linux || netbsd || openbsd
+//go:build darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris
 
 package poll
 
 import (
 	"io"
+	"runtime"
 	"syscall"
 )
 
@@ -29,6 +30,10 @@ func (fd *FD) Writev(v *[][]byte) (int64, error) {
 	// 1024 and this seems conservative enough for now. Darwin's
 	// UIO_MAXIOV also seems to be 1024.
 	maxVec := 1024
+	if runtime.GOOS == "solaris" {
+		// IOV_MAX is set to XOPEN_IOV_MAX on Solaris.
+		maxVec = 16
+	}
 
 	var n int64
 	var err error

src/internal/syscall/unix/writev_solaris.go

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build illumos
-
 package unix
 
 import (

src/net/writev_test.go

@@ -153,7 +153,7 @@ func testBuffer_writeTo(t *testing.T, chunks int, useCopy bool) {
 
 		var wantSum int
 		switch runtime.GOOS {
-		case "android", "darwin", "ios", "dragonfly", "freebsd", "illumos", "linux", "netbsd", "openbsd":
+		case "android", "darwin", "ios", "dragonfly", "freebsd", "illumos", "linux", "netbsd", "openbsd", "solaris":
 			var wantMinCalls int
 			wantSum = want.Len()
 			v := chunks

src/net/writev_unix.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build darwin || dragonfly || freebsd || illumos || linux || netbsd || openbsd
+//go:build darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris
 
 package net