bitbake: utils/md5_file: don't iterate line-by-line

Opening a file in binary mode and iterating it seems like the simple solution
but will still break on newlines, which for binary files isn't really useful as
the size of the chunks could be huge or tiny.

Instead, let's be a bit more clever: we'll be MD5ing lots of files, but we don't
want to fill up memory: use mmap() to open the file and read the file in 8k
blocks.

(Bitbake rev: a0ac8d67f1471a0c611d691b856fede67efb53f6)

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/utils.py

@@ -524,12 +524,17 @@ def md5_file(filename):
     """
     Return the hex string representation of the MD5 checksum of filename.
     """
-    import hashlib
-    m = hashlib.md5()
+    import hashlib, mmap
 
     with open(filename, "rb") as f:
-        for line in f:
-            m.update(line)
+        m = hashlib.md5()
+        try:
+            with mmap.mmap(f.fileno(), 0, access=mmap.ACCESS_READ) as mm:
+                for chunk in iter(lambda: mm.read(8192), b''):
+                    m.update(chunk)
+        except ValueError:
+            # You can't mmap() an empty file so silence this exception
+            pass
     return m.hexdigest()
 
 def sha256_file(filename):