Re: [FYI] tutorial for process record and reverse debugging

[Michael Snyder <msnyder@vmware.com>]

Greg Law wrote:
> Marc Khouzam wrote:
>>
>>> [...]
>>>> Or do you imagine it being the default?
>>>>
>>> FWIW, early versions of UndoDB operated in "Marc-mode".  We changed
>>> it because replay mode and record are quite different, particularly
>>> w.r.t. to the program's interaction with the outside world.
>>> "Silent" transition from replay to record mode could be quite
>>> confusing/surprising.
>> In cases where the program does interact with the outside world, I
>> agree that "auto-mode" could be confusing.  In fact, "record mode" 
>> may not be the one we want in this case either.  For instance, in 
>> some cases I may want to re-execute instructions that affect the
>> outside world, even if I'm gone backwards.  In this case I would want
>> to use the recorded  data to go backwards, but never to go forward
>> (never use "replay mode").
> 
> I'm not completely sure of the behaviour of process record here, but
> UndoDB in replay mode is completely "neutered", in that the results of
> all system calls are 'synthesised'.  So if, say, in record mode your
> program unlinks a file, then in replay mode the fact the filename is no
> longer present on the filesystem doesn't matter - we don't really do an 
> unlink, we just replay the results of whatever unlink returned when in 
> record mode.

It's the same for process record.