1 files changed, 46 insertions, 0 deletions
diff --git a/src/os/readfrom_linux.go b/src/os/readfrom_linux.go
new file mode 100644
index 0000000..63ea45c
--- /dev/null
+++ b/src/os/readfrom_linux.go
@@ -0,0 +1,46 @@
+// Copyright 2020 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 os
+
+import (
+	"internal/poll"
+	"io"
+)
+
+var pollCopyFileRange = poll.CopyFileRange
+
+func (f *File) readFrom(r io.Reader) (written int64, handled bool, err error) {
+	// copy_file_range(2) does not support destinations opened with
+	// O_APPEND, so don't even try.
+	if f.appendMode {
+		return 0, false, nil
+	}
+
+	remain := int64(1 << 62)
+
+	lr, ok := r.(*io.LimitedReader)
+	if ok {
+		remain, r = lr.N, lr.R
+		if remain <= 0 {
+			return 0, true, nil
+		}
+	}
+
+	src, ok := r.(*File)
+	if !ok {
+		return 0, false, nil
+	}
+	if src.checkValid("ReadFrom") != nil {
+		// Avoid returning the error as we report handled as false,
+		// leave further error handling as the responsibility of the caller.
+		return 0, false, nil
+	}
+
+	written, handled, err = pollCopyFileRange(&f.pfd, &src.pfd, remain)
+	if lr != nil {
+		lr.N -= written
+	}
+	return written, handled, NewSyscallError("copy_file_range", err)
+}