Using system call for downloading files

Using system call `sendfile` for downloading files using glance
image service. It's more efficient than passing the entire image
through Python `shutil`.

Change-Id: Ic36c593538fd97d3ac02d3ad77feebcfdb9f1868
Closes-Bug: #1199522

ironic/common/glance_service/base_image_service.py

@@ -17,10 +17,12 @@
 
 import functools
 import logging
-import shutil
+import os
 import sys
 import time
 
+import sendfile
+
 from glanceclient import client
 import six.moves.urllib.parse as urlparse
 
@@ -209,14 +211,8 @@ class BaseImageService(object):
             url = urlparse.urlparse(location)
             if url.scheme == "file":
                 with open(url.path, "r") as f:
-                    #TODO(ghe): Use system call for downloading files.
-                    # Bug #1199522
-
-                    # FIXME(jbresnah) a system call to cp could have
-                    # significant performance advantages, however we
-                    # do not have the path to files at this point in
-                    # the abstraction.
-                    shutil.copyfileobj(f, data)
+                    filesize = os.path.getsize(f.name)
+                    sendfile.sendfile(data.fileno(), f.fileno(), 0, filesize)
                 return
 
         image_chunks = self.call(method, image_id)

requirements.txt

@@ -19,6 +19,7 @@ python-neutronclient>=2.3.4,<3
 python-glanceclient>=0.9.0
 python-keystoneclient>=0.8.0
 stevedore>=0.14
+pysendfile==2.0.0
 websockify>=0.5.1,<0.6
 oslo.config>=1.2.0
 oslo.rootwrap