[Simh] porting RL01 images to RL02

[Johnny Billquist]

On 2017-02-06 22:10, Paul Koning wrote:
>
>> On Feb 5, 2017, at 6:25 PM, Paul Koning <paulkoning at comcast.net> wrote:
>>
>>
>>> On Feb 5, 2017, at 3:31 PM, Mark Pizzolato <Mark at infocomm.com> wrote:
>>>
>>> ...
>>>
>>> So, I'd like to expand the set of file system types that the auto sizing logic can perform
>>> to include RSTS disks and whatever might be commonly used with RSX and RT11.
>
> A possible complication with RSTS: I can't find the precise device size because that isn't stored anywhere in the file structure.  What I can find is the size rounded up to the next multiple of 4096 times the cluster size (from the free space bitmap size in blocks, since each bit represents a free cluster).  I can also find a lower bound, from the end of the last free cluster in the bitmap.  But if some of the space at the end of the pack is in use -- not all that common but certainly possible -- then that doesn't help.
>
> So if given a table of possible sizes for the controller model in question, this is certainly doable.  If two possible devices have sizes that are close it wouldn't always be possible to get the right answer.  Real disks are probably ok, but MSCP disks with user-selected sizes not corresponding to actual DEC models are likely to be a problem.
>
> Does the autosize routine have access to the controller model designation?

I suspect the need is mostly to determine when the code should give an 
error that you are accessing blocks outside the disk. If the actual 
image file was not preallocated to the correct size, you face a dilemma 
in simh. Access beyond current eof may, or may not be legitimate.

I would say that your upper bound calculation is good enough. A small 
rounding error giving a few extra blocks are probably ok.

This is done for MSCP and Massbus disks. So I don't think controller 
model identifications help.

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
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