Implement Read/WriteAtCurrentPos correctly

base/platform_file_posix.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/platform_file.h"
 
 #include <fcntl.h>
 #include <errno.h>
 #include <sys/stat.h>
 #include <unistd.h>
@@ skipping 243 matching lines @@
 }
 
 int ReadPlatformFileAtCurrentPos(PlatformFile file, char* data, int size) {
   base::ThreadRestrictions::AssertIOAllowed();
   if (file < 0 || size < 0)
     return -1;
 
   int bytes_read = 0;
   int rv;
   do {
-    rv = HANDLE_EINTR(read(file, data, size));
+    rv = HANDLE_EINTR(read(file, data + bytes_read, size - bytes_read));
     if (rv <= 0)
       break;
 
     bytes_read += rv;
   } while (bytes_read < size);
 
   return bytes_read ? bytes_read : rv;
 }
 
 int ReadPlatformFileNoBestEffort(PlatformFile file, int64 offset,
@@ skipping 40 matching lines @@
 
 int WritePlatformFileAtCurrentPos(PlatformFile file,
                                   const char* data, int size) {
   base::ThreadRestrictions::AssertIOAllowed();
   if (file < 0 || size < 0)
     return -1;
 
   int bytes_written = 0;
   int rv;
   do {
-    rv = HANDLE_EINTR(write(file, data, size));
+    rv = HANDLE_EINTR(write(file, data + bytes_written, size - bytes_written));
     if (rv <= 0)
       break;
 
     bytes_written += rv;
   } while (bytes_written < size);
 
   return bytes_written ? bytes_written : rv;
 }
 
 int WritePlatformFileCurPosNoBestEffort(PlatformFile file,
@@ skipping 120 matching lines @@
     default:
 #if !defined(OS_NACL)  // NaCl build has no metrics code.
       UMA_HISTOGRAM_SPARSE_SLOWLY("PlatformFile.UnknownErrors.Posix",
                                   saved_errno);
 #endif
       return PLATFORM_FILE_ERROR_FAILED;
   }
 }
 
 }  // namespace base