[Fedora-livecd-list] [patch 00/20] Fix error handling and misc. cleanups

[Mark McLoughlin]

Hi,
	Apologies for spamming the list with 20 mails, but hopefully
it'll make it easier to review the patches.

	The background to this is that I was suprised to see that
livecd-creator had rather poor error handling (e.g. not unmounting
stuff after certain errors, obscure error messages etc.) since
I thought that was the main reason to re-write pilgrim in python :-)

	It's understandable, though. Because Python has exceptions,
it's easy to be fooled into thinking you have error conditions
under control, but in reality, exceptions probably makes it easier
to screw up error handling.

	So, here's an attempt to fix it based on the following
guidelines:

  - don't intercept an exception if you can't do something useful
    with it. Corollary: intercept an exception if you can do something
    useful with it.

  - anticipate user errors or user-fixable system errors in a user
    friendly manner. Corollary: allow other types of exceptions
    to be passed to the toplevel.

  - i.e. there are 3 types of errors/exceptions, and 3 different
    strategies for handling them:

      1) errors which we can handle ourselves without ever telling
         the user - e.g. a directory which we wish to create already
         exists

      2) user errors, or predictable system errors, which we
         should do our best to help the user out with -  e.g.
         a busted kickstart file or running out of loop devices

      3) pathological system errors or programmer errors, all
         of which can be just allowed to propogate up to the
         toplevel where an ugly traceback will be printed -
         e.g creating a dir under the temporary build dir
         fails or an unmount fails because we didn't close
         the rpmdb

  - whatever the error, we should do our best to clean up files,
    directories, mounts, etc. which we created

  - bear in mind that e.g. Ctrl-C can happen at any time

	Also, I've cleanup up various parts of the code as I
worked on the error handling. Those patches come first.

Cheers,
Mark.

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