Wondering if the proposed new command could actually be added at
the CP level instead of the CMS/MVS level.
CP might save the state of the machine to a prepared location in
DASD then restore it when the user next logs in, essentially
mimicking the VMWare (for example) suspend/restore capability.?
Users can already disconnect and leave the machine intact to
reconnect to it later (even leaving it running in the background),
so from a user perspective this would extend that with the option
to reconnect to it even after a shutdown / re-ipl of VM, but
without leaving it running in between.
There would obviously be limits to this when working with
dedicated hardware, but for virtualized hardware as with a typical
CMS machine, I would think it could be done (granted with a fair
amount of effort)?
On 3/27/24 00:23, Bertram Moshier
wrote:
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Hello Harold,
What you desire doesn't exist in VM/370 today, but it is
possible.? Cray Supercomputers are real memory systems that
use swapping to allow multiple users to use the same real
memory space.? IBM went with paging for its solution to this
problem.? Seymore Cray rejected this method because it added
around seven cycles?to each operation referencing?memory.
Let us see if I understand you correctly.? You want to take
a snapshot of a virtual machine's memory (e.g., 0 to maximum
storage size of the machine).? How you accomplish this depends
upon what you want to do with the image and the memory
methodology used by the users' virtual machine operating
system.
There are two methods for collecting a copy of the memory
for offline examination.? They are:
1) Copy the state of the virtual machine to a binary
file.? What we used for the Cray IBM VM Station. When an
error occurred, the station would dump all of its memory,
registers, etc., to a file. We had tools to examine the
station and even run it to the point of failure. (We would
use the internal trace to simulate the interrupts and data
transmissions (to and from the Cray and users' virtual
machines).) This improved the station's stability?so we
could catch coding and design issues before shipping the
product to customers.
2)? You could (as Bob suggested) use the existing CP DUMP
command.? A better solution would be to allow CP to dump the
data more than the printer.
On the other hand, if you want to stop and restart an
operating system without regard to space or time and support
both paging and swapping, you will need to add a new command
to the operating system. This would be similar to Windows
hibernation but with more functionality.? As this new command
is at the operating system level (e.g., MVS), it would support
both real and virtual environments.
Bertram Moshir
WB8ERT
For
my Stand Alone Tool Kit project I am working on the ability to
create a formatted memory dump.? It depends upon preserving
the
machine's memory in a host (Windows, Linux, etc.) platform's
host file
system.? With Hercules this is accomplished using the Hercules
command
'savecore'.
SATK is sometimes used with z/VM virtual machines.? So, I am
asking:
is it possible to transfer the contents of a virtual machine's
physical
(absolute storage) memory out of VM (any version, VM/370 or
z/VM) in any
manner at all?
The assumption is that a bare-metal program has been executing
within
the virtual machine, so CMS is out of the picture.? This would
strictly
be CP commands as I understand things.
Assuming the storage contents exists outside of the virtual
machine,
whatever format that turns out to be, can be manipulated for
use by the
dump program.? Separate problem for later.
Note, I am not opposed to a programmatic approach from within
the
virtual machine embedded within the bare-metal program if
required to
get the memory content out of the virtual machine, BUT only if
that is
the only way.
Asking the experts...
Harold Grovesteen
