xfer-hole: Fix bug in copy_slice_from_file.

os.read is limited to an int in size. copy_slice_from_file was trying
to os.read more than that causing an OverflowError.

1 files changed, 8 insertions, 2 deletions

diff --git a/morphlib/xfer-hole b/morphlib/xfer-hole
index 0d4cee7a..22ee06bf 100755
--- a/morphlib/xfer-hole
+++ b/morphlib/xfer-hole
@@ -120,8 +120,14 @@ def make_xfer_instructions(fd):
 
 def copy_slice_from_file(to, fd, start, end):
     safe_lseek(fd, start, os.SEEK_SET)
-    data = os.read(fd, end - start)
-    to.write(data)
+    nbytes = end - start
+    max_at_a_time = 1024**2
+    while nbytes > 0:
+        data = os.read(fd, min(nbytes, max_at_a_time))
+        if not data:
+            break
+        to.write(data)
+        nbytes -= len(data)
     
 
 for kind, start, end in make_xfer_instructions(fd):