code review 4538088: http,io,net: sendfile support

src/pkg/net/sendfile_linux.go

 // Copyright 2011 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.
 
 package net
 
 import (
         "fmt"
         "io"
         "os"
         "syscall"
         "unsafe"
 )
 
 const maxSendfileSize int64 = 4 << 20 // arbitrary size that fits in an int
 
-// SendFile sends f to c using sendfile(2), bypassing userspace copies,
-// if possible. If n >= 0, it specifies the max number of bytes to copy.
-// If n < 0, it means until EOF. SendFile returns the number of bytes copied
-// and any error, if not EOF.
+// SendFile copies the contents of f to c, avoiding unnecessary copies
+// where possible.
+//
+// If n >= 0, n specifies the maximum number of bytes to copy.
+// If n < 0, Sendfile copies until EOF
+
+// SendFile returns the number of bytes copied and any error, if not
+// EOF.
 func (c *TCPConn) SendFile(f *os.File, n int64) (written int64, err os.Error) {
         destfd := c.fd.sysfd
         srcfd := f.Fd()
         for {
                 toCopy := maxSendfileSize
                 if n >= 0 {
                         toCopy = n - written
                         if toCopy > maxSendfileSize {
                                 toCopy = maxSendfileSize
                         }
                 }
                 if toCopy <= 0 {
                         return
                 }
-                sn, err := syscall.Sendfile(destfd, srcfd, (*int64)(unsafe.Pointer(nil)), int(toCopy))
-                switch err {
+                sn, errno := syscall.Sendfile(destfd, srcfd, (*int64)(unsafe.Pointer(nil)), int(toCopy))
+                switch errno {
                 case 0:
                         if n == 0 {
                                 return written, nil
                         }
                         written += int64(sn)
                 case syscall.EAGAIN:
                         pollserver.WaitWrite(c.fd)
                 default:
                         return written, fmt.Errorf("io: sendfile error %d", err)
                 }
@@ skipping 27 matching lines @@
                         return written, nil
                 }
                 if written != 0 {
                         return written, err
                 }
                 // if sendfile failed, but didn't copy any bytes, fall through...
         }
 
         return io.BufferedCopyn(c, r, n)
 }