[Libguestfs] [PATCH] Improve memory management of nbdkit python plugin example

Hi, the nbdkit python plugin example has suboptimal memory management: - it creates the disk image as a string on init - it casts the string to bytearray on every read - it copies the string before and the string after the written region, then reassembles those pieces together with the written region to a new disk image string This is not a problem as long as the image is small, but in my tests with a 5 GB sized image nbdkit already used 15 GB RAM directly after startup, and even more (20-25 GB) on the first write. This changes the code to use bytearray everywhere and use the proper methods to change bytearray objects directly. With the patch applied, nbdkit with a 5 GB image will still only use 5 GB RAM even during heavy read/write activity. Regards, Carl-Daniel diff -r 521366d1854b -r d7d5078d08c7 plugins/python/example.py --- a/plugins/python/example.py Sun Jul 10 17:10:30 2016 +0100 +++ b/plugins/python/example.py Sun Sep 25 05:04:02 2016 +0200 @@ -29,7 +29,7 @@ # reconnect to the same server you should see the same disk. You # could also put this into the handle, so there would be a fresh disk # per handle. -disk = "\0" * (1024*1024); +disk = bytearray(1024 * 1024) # This just prints the extra command line parameters, but real plugins # should parse them and reject any unknown parameters. @@ -50,9 +50,9 @@ def pread(h, count, offset): global disk - return bytearray (disk[offset:offset+count]) + return disk[offset:offset+count] def pwrite(h, buf, offset): global disk end = offset + len (buf) - disk = disk[:offset] + buf + disk[end:] + disk[offset:end] = buf