[Libguestfs] [PATCH libnbd v3 0/2] lib: Implement closure lifetimes.

[Richard W.M. Jones]

I think I've addressed everything that was raised in review.
Some of the highlights:

 - Callbacks should be freed reliably along all exit paths.

 - There's a simple test of closure lifetimes.

 - I've tried to use VALID|FREE in all the places where I'm confident
   that it's safe and correct to do.  There may be more places.  Note
   this is an optimization and shouldn't affect correctness.

 - It's a bit difficult to use VALID|FREE when freeing the debug
   callback (because context is not easily available) so I didn't make
   that change.

Rich.