[Infrastructures] state machines

[Brandon S. Allbery KF8NH]

On Sep 19, 2006, at 11:40 AM, Wesley Craig wrote:

> On 19 Sep 2006, at 11:18, Brandon S. Allbery KF8NH wrote:
>> On Sep 19, 2006, at 9:44 AM, Wesley Craig wrote:
>>> Stated so generally, I think I can come up with counter  
>>> examples.  For instance, if you make a full disk image before  
>>> pushing out a change, you can in fact "undo" the change, by  
>>> restoring the backup.
>>
>> ...unless said change affects something other than disk ---  
>> consider PC BIOS, or more significantly the SPARC/PPC "eeprom"  
>> command.
>
> Sure.  Think you can come up with a solution for that situation?   
> State machines are just that.  If you are able to record the state,  
> you can restart.  It's that simple.

Sure --- assuming you know all of the state that is ever affected by  
any change.  Which is in some sense the fundamental issue here; I do  
*not* reliably know everything that e.g. Cadence installs will  
affect, and once or twice we've been caught by surprise as a result.   
State machines are only useful when *all* possible states are known  
beforehand.

-- 
brandon s. allbery     [linux,solaris,freebsd,perl]       
allbery@kf8nh.com
system administrator  [openafs,heimdal,too many hats]   
allbery@ece.cmu.edu
electrical and computer engineering, carnegie mellon university       
KF8NH