1 files changed, 81 insertions, 0 deletions
diff --git a/src/internal/poll/writev.go b/src/internal/poll/writev.go
new file mode 100644
index 0000000000..fcee388513
--- /dev/null
+++ b/src/internal/poll/writev.go
@@ -0,0 +1,81 @@
+// Copyright 2016 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 darwin dragonfly freebsd linux netbsd openbsd
+
+package poll
+
+import (
+	"io"
+	"syscall"
+	"unsafe"
+)
+
+// Writev wraps the writev system call.
+func (fd *FD) Writev(v *[][]byte) (n int64, err error) {
+	if err := fd.writeLock(); err != nil {
+		return 0, err
+	}
+	defer fd.writeUnlock()
+	if err := fd.pd.prepareWrite(); err != nil {
+		return 0, err
+	}
+
+	var iovecs []syscall.Iovec
+	if fd.iovecs != nil {
+		iovecs = *fd.iovecs
+	}
+	// TODO: read from sysconf(_SC_IOV_MAX)? The Linux default is
+	// 1024 and this seems conservative enough for now. Darwin's
+	// UIO_MAXIOV also seems to be 1024.
+	maxVec := 1024
+
+	for len(*v) > 0 {
+		iovecs = iovecs[:0]
+		for _, chunk := range *v {
+			if len(chunk) == 0 {
+				continue
+			}
+			iovecs = append(iovecs, syscall.Iovec{Base: &chunk[0]})
+			if fd.IsStream && len(chunk) > 1<<30 {
+				iovecs[len(iovecs)-1].SetLen(1 << 30)
+				break // continue chunk on next writev
+			}
+			iovecs[len(iovecs)-1].SetLen(len(chunk))
+			if len(iovecs) == maxVec {
+				break
+			}
+		}
+		if len(iovecs) == 0 {
+			break
+		}
+		fd.iovecs = &iovecs // cache
+
+		wrote, _, e0 := syscall.Syscall(syscall.SYS_WRITEV,
+			uintptr(fd.Sysfd),
+			uintptr(unsafe.Pointer(&iovecs[0])),
+			uintptr(len(iovecs)))
+		if wrote == ^uintptr(0) {
+			wrote = 0
+		}
+		TestHookDidWritev(int(wrote))
+		n += int64(wrote)
+		consume(v, int64(wrote))
+		if e0 == syscall.EAGAIN {
+			if err = fd.pd.waitWrite(); err == nil {
+				continue
+			}
+		} else if e0 != 0 {
+			err = syscall.Errno(e0)
+		}
+		if err != nil {
+			break
+		}
+		if n == 0 {
+			err = io.ErrUnexpectedEOF
+			break
+		}
+	}
+	return n, err
+}