unix: add Linux CopyFileRange syscall

Introduces the CopyFileRange syscall which first appears in Linux 4.5.
Allows copying file content between file descriptors within the kernel
without transferring data to user space. This syscall also allows the
kernel to take advantage of reflinking or other fast copy methods on
supported file systems.
http://man7.org/linux/man-pages/man2/copy_file_range.2.html

Change-Id: Id365f1e5d4d5ddf7159478e3a13084c9576ebd5c
Reviewed-on: https://go-review.googlesource.com/39992
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/unix/zsyscall_linux_mips64.go b/unix/zsyscall_linux_mips64.go
index 1f97828..60c9629 100644
--- a/unix/zsyscall_linux_mips64.go
+++ b/unix/zsyscall_linux_mips64.go
@@ -312,6 +312,17 @@
 
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
+func CopyFileRange(rfd int, roff *int64, wfd int, woff *int64, len int, flags int) (n int, err error) {
+	r0, _, e1 := Syscall6(SYS_COPY_FILE_RANGE, uintptr(rfd), uintptr(unsafe.Pointer(roff)), uintptr(wfd), uintptr(unsafe.Pointer(woff)), uintptr(len), uintptr(flags))
+	n = int(r0)
+	if e1 != 0 {
+		err = errnoErr(e1)
+	}
+	return
+}
+
+// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
+
 func Dup(oldfd int) (fd int, err error) {
 	r0, _, e1 := Syscall(SYS_DUP, uintptr(oldfd), 0, 0)
 	fd = int(r0)