[CRIU] rewriting images via criu (or crit?)

[Ruslan Kuprieiev]

Hi all,

I was recently thinking about converting/modifying images and i want to 
share some of my thoughts.
For now I see 4 main ways:

1) Use existing patch set for crit written in python.
Pros:
     1. Already works.
     2. Python project is easy to support.
     3. Adding xpath-like language for modifying images should be easy 
in Python.
     4. All needed dependencies are available in (any?) repo.
Cons:
     1. Performance(maybe we could use Cython to make it better?).

2) Rewrite crit in C
Pros:
     1. Performance.
Cons:
     1. C project is hard to support.
     3. Adding xpath-like language for modifying images is not as easy 
as in Python.
     4. Requires protobuf-c-text, which is quite new and isn't available 
in repos.

3) Add crit functionality to criu ("criu convert", "criu modify").
Pros:
     1. Performance
     2. Allows us to reuse a bunch of existing code.
     3. Having such tool shipped along with "criu show" looks like a 
nice feature.
     4. We can easily teach criu how to use images in text format, which 
seems
         quite handy.
Cons:
     1. criu is already complex enough and adding more stuff might be 
too much,
         especially xpath-like language engine.
     2. Hard to support.
     3. Requires protobuf-c-text, which is quite new and isn't available 
in repos.
     4. Requires heavy patching to existing code.

4) Use 1), but for _high-speed_ image modification use criu plugins and 
hooks
     to modify images on restore.
Pros:
     1. Performance.
     2. No heavy patching.
Cons:
     Can't see any.

I prefer 4) because it seems like a good compromise.
What do you guys think?