From 51f2932082ecfc7c92aad774be3ebea6436d662b Mon Sep 17 00:00:00 2001
From: Rob Pike <r@golang.org>
Date: Wed, 9 Dec 2009 14:18:32 -0800
Subject: [PATCH] syscalls can return negative i/o counts. fix bugs in ReadAt
 and WriteAt not to include negative counts in return values.

R=rsc
CC=golang-dev
https://golang.org/cl/170044
---
 src/pkg/os/file.go | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/pkg/os/file.go b/src/pkg/os/file.go
index 03c6d57018..459b78cc22 100644
--- a/src/pkg/os/file.go
+++ b/src/pkg/os/file.go
@@ -141,11 +141,11 @@ func (file *File) ReadAt(b []byte, off int64) (n int, err Error) {
 		if m == 0 && e == 0 {
 			return n, EOF
 		}
-		n += m;
 		if e != 0 {
 			err = &PathError{"read", file.name, Errno(e)};
 			break;
 		}
+		n += m;
 		b = b[m:];
 		off += int64(m);
 	}
@@ -186,11 +186,11 @@ func (file *File) WriteAt(b []byte, off int64) (n int, err Error) {
 	}
 	for len(b) > 0 {
 		m, e := syscall.Pwrite(file.fd, b, off);
-		n += m;
 		if e != 0 {
 			err = &PathError{"write", file.name, Errno(e)};
 			break;
 		}
+		n += m;
 		b = b[m:];
 		off += int64(m);
 	}
-- 
2.50.0