internal/poll, net, syscall: enable writev on aix

aix supports iovec read/write, see
https://www.ibm.com/docs/en/aix/7.2?topic=w-write-writex-write64x-writev-writevx-ewrite-ewritev-pwrite-pwritev-subroutine

Define an unexported writev wrapper in package syscall (like on openbsd
and darwin) and linkname it from internal/poll.

Change-Id: I8f9695ceac72ae861afa3692207c154d86d4e690
Reviewed-on: https://go-review.googlesource.com/c/go/+/435260
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>

src/internal/poll/fd_writev_libc.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 || (openbsd && !mips64)
+//go:build aix || darwin || (openbsd && !mips64)
 
 package poll
 

src/internal/poll/iovec_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 || linux || netbsd || openbsd
+//go:build aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd
 
 package poll
 

src/internal/poll/writev.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 || linux || netbsd || openbsd || solaris
+//go:build unix
 
 package poll
 
@@ -30,8 +30,8 @@ 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.
+	if runtime.GOOS == "aix" || runtime.GOOS == "solaris" {
+		// IOV_MAX is set to XOPEN_IOV_MAX on AIX and Solaris.
 		maxVec = 16
 	}
 

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", "solaris":
+		case "aix", "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 || linux || netbsd || openbsd || solaris
+//go:build unix
 
 package net
 

src/syscall/syscall_aix.go

@@ -642,6 +642,7 @@ func PtraceDetach(pid int) (err error) { return ptrace64(PT_DETACH, int64(pid),
 //sys	Unlink(path string) (err error)
 //sysnb	Uname(buf *Utsname) (err error)
 //sys	write(fd int, p []byte) (n int, err error)
+//sys	writev(fd int, iovecs []Iovec) (n uintptr, err error)
 
 //sys	gettimeofday(tv *Timeval, tzp *Timezone) (err error)
 

src/syscall/zsyscall_aix_ppc64.go

@@ -96,6 +96,7 @@ import "unsafe"
 //go:cgo_import_dynamic libc_Unlink unlink "libc.a/shr_64.o"
 //go:cgo_import_dynamic libc_Uname uname "libc.a/shr_64.o"
 //go:cgo_import_dynamic libc_write write "libc.a/shr_64.o"
+//go:cgo_import_dynamic libc_writev writev "libc.a/shr_64.o"
 //go:cgo_import_dynamic libc_gettimeofday gettimeofday "libc.a/shr_64.o"
 //go:cgo_import_dynamic libc_mmap mmap "libc.a/shr_64.o"
 //go:cgo_import_dynamic libc_munmap munmap "libc.a/shr_64.o"
@@ -189,6 +190,7 @@ import "unsafe"
 //go:linkname libc_Unlink libc_Unlink
 //go:linkname libc_Uname libc_Uname
 //go:linkname libc_write libc_write
+//go:linkname libc_writev libc_writev
 //go:linkname libc_gettimeofday libc_gettimeofday
 //go:linkname libc_mmap libc_mmap
 //go:linkname libc_munmap libc_munmap
@@ -285,6 +287,7 @@ var (
 	libc_Unlink,
 	libc_Uname,
 	libc_write,
+	libc_writev,
 	libc_gettimeofday,
 	libc_mmap,
 	libc_munmap libcFunc
@@ -1381,6 +1384,21 @@ func write(fd int, p []byte) (n int, err error) {
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
+func writev(fd int, iovecs []Iovec) (n uintptr, err error) {
+	var _p0 *Iovec
+	if len(iovecs) > 0 {
+		_p0 = &iovecs[0]
+	}
+	r0, _, e1 := syscall6(uintptr(unsafe.Pointer(&libc_writev)), 3, uintptr(fd), uintptr(unsafe.Pointer(_p0)), uintptr(len(iovecs)), 0, 0, 0)
+	n = uintptr(r0)
+	if e1 != 0 {
+		err = errnoErr(e1)
+	}
+	return
+}
+
+// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
+
 func gettimeofday(tv *Timeval, tzp *Timezone) (err error) {
 	_, _, e1 := syscall6(uintptr(unsafe.Pointer(&libc_gettimeofday)), 2, uintptr(unsafe.Pointer(tv)), uintptr(unsafe.Pointer(tzp)), 0, 0, 0, 0)
 	if e1 != 0 {