[Simh] RQ disk formats broken in the latest build?

[Mark Pizzolato]

On Tuesday, April 10, 2018 at 11:25 AM, Robert Armstrong wrote:
> >I suspect that might be ok.

In general reading and writing the data in a file in "RAW" mode vs "SIMH" mode should produce the same result.  RAW uses open,read,write and close, while SIMH uses the C RTL fopen,fread,fwrite, and fclose.  The C RTL does I/O when it thinks it needs to using buffers (I/O size) that it likes.  RAW I/O uses the buffers (and I/O size) explicitly provided by the calling program.

As it turns out, you can successfully open a CDROM drive with either RAW or CRTL APIs, however read I/O to the CDROM generally has sector size and alignment concerns that the aren't well behaved using the CRTL's buffering.

To address this, RQ disk container files  are now first opened in RAW mode and if that succeeds, things proceed just fine.  If the RAW open fails (for whatever reason) things fall back to using CRTL I/O.  So, for most files, you'll see them being accessed in RAW mode going forward, but as Johnny says it shouldn't matter one way or another.

>   Well, empirically it doesn't work.  The file foo.rd54 is never created and the
> disk appears offline to any guest OK.  Not OK.  Sorry.

This is a case I didn't test (attach a non-existing file) on Linux/Unix.  What is happening here is that open is being called with mode O_RDONLY and that open succeeds and you see the strange behavior.

This is fixed now.

- Mark