Add --chunk-size option to set size of chunks.

Previous hard-coded value is now just the default.
Some day the default should be upped for more speed.

4 files changed, 13 insertions, 5 deletions

diff --git a/blackboxtest b/blackboxtest
index 61ab18b9..7f09bbf6 100755
--- a/blackboxtest
+++ b/blackboxtest
@@ -401,7 +401,9 @@ class UsesChunkGroups(BlackBoxTest):
     def test(self):
         data = self.tempdir()
         ngroups = 2
-        nbytes = obnamlib.CHUNK_SIZE * obnamlib.CHUNK_GROUP_SIZE * ngroups
+        nbytes = (obnamlib.DEFAULT_CHUNK_SIZE * 
+                  obnamlib.DEFAULT_CHUNK_GROUP_SIZE * 
+                  ngroups)
         self.create_file(data, 'file', 'x' * nbytes)
         store = self.tempdir()
         self.backup(store, [data])
diff --git a/obnamlib/__init__.py b/obnamlib/__init__.py
index b1952403..1f53237f 100644
--- a/obnamlib/__init__.py
+++ b/obnamlib/__init__.py
@@ -26,8 +26,8 @@ class AppException(Exception):
 class Error(Exception):
     pass
 
-CHUNK_SIZE = 4096
-CHUNK_GROUP_SIZE = 16
+DEFAULT_CHUNK_SIZE = 4096
+DEFAULT_CHUNK_GROUP_SIZE = 16
 
 from sizeparse import SizeSyntaxError, UnitNameError, ByteSizeParser
 
diff --git a/obnamlib/app.py b/obnamlib/app.py
index 8f7401f0..b460bee7 100644
--- a/obnamlib/app.py
+++ b/obnamlib/app.py
@@ -42,6 +42,11 @@ class App(object):
                                 'do not write or remove anything, just '
                                 'pretend to do that')
 
+        self.config.new_bytesize(['chunk-size'],
+                                 'size of chunks of file data backed up '
+                                 '(default: %default)')
+        self.config['chunk-size'] = '%s' % obnamlib.DEFAULT_CHUNK_SIZE
+
         self.pm = obnamlib.PluginManager()
         self.pm.locations = [self.plugins_dir()]
         self.pm.plugin_arguments = (self,)
diff --git a/obnamlib/plugins/backup_plugin.py b/obnamlib/plugins/backup_plugin.py
index 0f7f4cdc..4d2dbb6c 100644
--- a/obnamlib/plugins/backup_plugin.py
+++ b/obnamlib/plugins/backup_plugin.py
@@ -190,13 +190,14 @@ class BackupPlugin(obnamlib.ObnamPlugin):
         cgids = []
         groupsum = self.store.new_checksummer()
         f = self.fs.open(filename, 'r')
+        chunk_size = int(self.app.config['chunk-size'])
         while True:
-            data = f.read(obnamlib.CHUNK_SIZE)
+            data = f.read(chunk_size)
             if not data:
                 break
             chunkids.append(self.backup_file_chunk(data))
             groupsum.update(data)
-            if len(chunkids) == obnamlib.CHUNK_GROUP_SIZE:
+            if len(chunkids) == obnamlib.DEFAULT_CHUNK_GROUP_SIZE:
                 checksum = groupsum.hexdigest()
                 cgid = self.store.put_chunk_group(chunkids, checksum)
                 cgids.append(cgid)