[Simh] Fwd: Making tape/disk images

[Ken Cornetet]

Not sure you need to go to the effort. Most simh hosts already have a perfectly usable tar and it is trivial to convert a file into a simh tape image.

Now, what would be handy is a portable (c, perl, etc) of your guest OS native tape archiving tool, if it has no way to read or write tar tapes.

But that has little to do with the original discussion.  In the original discussion, we aren’t talking about having simh know anything about guest OS tape handling, file systems, or archive programs. Simh handles tapes the same regardless of OS. Virtual tapes consist of “files”. These tape files consist of variable length records.

What we are talking about doing is adding simh code to allow attaching a directory as a tape device. Remember, a virtual tape needs “files” consisting of records. We know how to build the file information (logical file = physical file). Next, we need record length. For this we have two options:  User specified fixed size records or text file records. You’d have to supply this information to simh when attaching the tape device.

Simple so far. However, the devil is in the details. How to sort files in the folder (date or name). How to handle backward tape reading. When to read the directory to get a list of files. What if a physical file gets deleted? This would all have to be worked out, but I think it is doable.

From: simh-bounces at trailing-edge.com [mailto:simh-bounces at trailing-edge.com] On Behalf Of Michael Richter
Sent: Wednesday, May 05, 2010 9:46 AM
To: simh
Subject: [Simh] Fwd: Making tape/disk images

Oops.  Sent this to Tim only instead of list.
---------- Forwarded message ----------
From: Michael Richter <ttmrichter at gmail.com<mailto:ttmrichter at gmail.com>>
Date: 5 May 2010 21:45
Subject: Re: [Simh] Making tape/disk images
To: "Shoppa, Tim" <tshoppa at wmata.com<mailto:tshoppa at wmata.com>>

On 5 May 2010 20:59, Shoppa, Tim <tshoppa at wmata.com<mailto:tshoppa at wmata.com>> wrote:
Al writes:
> On 5/3/10 12:30 PM, Tim Newsham wrote:
>> the code that reads tape images in simh can also
>> read from a directory instead of a tape image.
>

>and create what type of on-tape directory structure?

>tape image code knows of nothing above tape blocks and
>file marks.
Al hits the issue exactly on the head.

If SIMH only had to emulate one operating system, with one OS/application tape format, then I think the concept of a "virtual filesystem tape image" would be OK.

But SIMH is used with dozens of OS's, with hundreds of different tape formats. Seems like things spin out of control to support them all inside SIMH.

Now, tools that can manipulate files and load them into tape and disk images in OS-specific formats, or go the other way and extract files from tape and disk images, has a long tradition. Going back to at least the 1970's. My gut feeling is to extend this tradition, not abandon it.

Would it not be possible to make a general-purpose tape archive system that has mid-end plugins for the OS-specific formats and back-end plug-ins for the simulated physical formats?  This way a single tool with a single command line could be made that allows things like (example command lines only):

 *   simtar --create --file=myfile.tap --file-system=RSTS9 --tape-format=SIMH ./*
 *   simtar --extract --file=myfile.tcp --file-system=VMS --tape-format=TPC
Unless someone can see any reason why this is intrinsically impossible, I wouldn't mind taking a crack at such a program written in some scripting language for proof of concept (and maybe even final form -- I don't see any particular advantage to writing something like this in C since performance won't be a huge issue).  Since I'm screwing around with RSTS right now my first version would be for RSTS, naturally.  I could then pop the code up somewhere for others to hack onto for other formats.  As new emulators get attached, new operating systems get resurrected, etc. the program could be expanded with plug-ins.

--
"Perhaps people don't believe this, but throughout all of the discussions of entering China our focus has really been what's best for the Chinese people. It's not been about our revenue or profit or whatnot."
--Sergey Brin, demonstrating the emptiness of the "don't be evil" mantra.



--
"Perhaps people don't believe this, but throughout all of the discussions of entering China our focus has really been what's best for the Chinese people. It's not been about our revenue or profit or whatnot."
--Sergey Brin, demonstrating the emptiness of the "don't be evil" mantra.
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