[Simh] Disk sizing

[Mark Pizzolato]

On Monday, February 6, 2017 at 12:39 PM, Johnny Billquist wrote:
> On 2017-02-06 19:38, Mark Pizzolato wrote:
> > Rather than that, please just give the latest github code a spin to
> > see if the
> > ODS1 volumes you have at your fingertips are correctly recognized when
> > they are attached to a RP or RQ device.
> 
> What can I expect to see? I mean, my images are already the correct size
> anyway, so the sizing should not result in any difference than today...
> I'll try it when I get a little time. Maybe this weekend. I guess it's time I
> updated my version of simh anyway. :-)

While processing the ATTACH command, if it detects a particular file system 
it announces what it has found and if auto sizing is enabled and the disk size 
is smaller than the file system size, then the disk size is expanded to allow 
access to the full useful extent of the disk container by the simulated system.  
If auto sizing is disabled, then a message explaining that data access errors are 
likely with the current size of the disk.

> > Bringing this functionality to other disk types is a project for
> > another day and might not provide much value since most, if not all,
> > of them had their last track written with BAD144 data.
> 
> Well, in the case of ODS, the code should work fine on any kind of disk, so
> there is really no reason to limit it to some controllers.

It is not a about a specifically limiting the functionality.  The code is built into 
the sim_disk functionality which currently is only used by the RQ and RP devices.

The project for another day is to either make the existing file system checking 
flexible enough to work for both the sim_disk using code and the legacy sim_fio 
code, OR to convert the RL and HK devices to use sim_disk.

> That said, all RP disks should have BAD144 data written anyway. Standard
> procedure in RSX is that before you create a file system, you should let the bad
> block scanner go over the disk, and create the BAD144 data, which the file
> system initialization code tries to read, in order to remove bad blocks from the
> usable filesystem.
> 
> > An interesting effect is that now all of the ODS1 and ODS2 disk images
> > which were originally created on other  device types (RK, RL, etc.)
> > can be attached to an RQ controller and be properly sized.
> 
> Yup. But it will cause them to be accessed with a "strange" controller, so don't
> try and boot them. :-)

Absolutely.  The boot block code will be completely wrong.

- Mark