We don't use swapgen for exactly this reason.  We define the vdisks in
the directory, and have an init script that runs very early in the Linux
boot that formats and enables the swap partitions.  Works fine, and
allows us to keep the configuration at a single point.

Remember, there's nothing magical about enabling swap.  It's done during
rc.sysinit, and unless the guest is VERY small, it's unlikely any of the
space will be required before the first init script is run.

We also use boot-time scripts to configure the network interfaces from
files stored on the 191 disk.  This way, the IP address can be 
changed without bringing up the guest.  Disadvantage is, every guest
needs its own 191 disk, but we get a lot of flexibility this way.

There are other ways to handle this I've thought of along the way, but
the basic principle is sound.

-----Original Message-----
From: Linux on 390 Port [mailto:[email protected]] On Behalf Of
Mark Post
Sent: Friday, January 16, 2009 11:56 AM
To: [email protected]
Subject: Re: [LINUX-390] SWAPGEN and PROFILE EXEC's

>>> On 1/16/2009 at  7:57 AM, Michael MacIsaac <[email protected]>
wrote: 
>>  I would rather control the VDISK sizes in the directory instead of
> having PROFILE EXEC
> Makes me wonder - can you pass parameters into PROFILE EXEC by setting
the
> directory?  e.g. "IPL CMS 300 524288 301 1048576"? Then use those
> parameters with SWAPGEN to make the correct vaddrs and swap space
sizes
> ... just a thought.

This assumes that no one does anything other than use those values.
Rob's point is that someone might do something different and hurt
overall system performance.  I think the idea of having the VDISK
defined in the directory, and using SWAPGEN's REUSE option that Rich
mentioned is the "safest" way to do this.  As at least one person on the
list has seen, if you allow "too much" VDISK to be defined and it
_gets_used_, it can really hurt you.

Regarding using PROFILE EXEC versus COMMAND statements in the CP
directory, there is a place for both.  One of the benefits of the
COMMAND statement is that it gets executed, regardless of the privileges
associated with the virtual machine.  So, you can have arbitrary guests
issue commands at logon time that they would not otherwise be able to in
PROFILE EXEC.  The conditional logic that PROFILE EXEC provides gives
you all sorts of other flexibiltiy.


Mark Post

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