Handle if ENODATA error and some data already written

Author: Bojan Nikolic

Lib/shutil.py

@@ -214,6 +214,16 @@ def _fastcopy_sendfile(fsrc, fdst):
                 # ENODATA: In rare cases, sendfile() on Linux Lustre
                 # returns ENODATA.
                 _USE_CP_SENDFILE = False
+
+                dstpos = os.lseek(outfd, 0, os.SEEK_CUR)
+                if dstpos > 0:
+                    # Some data has already been written but we use
+                    # sendfile in a mode that does not update the
+                    # input fd position when reading. Hence seek the
+                    # input fd to the correct position before falling
+                    # back on POSIX read/write method
+                    os.lseek(infd, dstpos, os.SEEK_SET)
+                    
                 raise _GiveupOnFastCopy(err)
 
             if err.errno == errno.ENOSPC:  # filesystem is full