We're running into an unnecessary ugliness in zSeries
with respect to booting and configuration. We need "the PARM parm".
There's a concept of a "boot command-line". This is good.
Often, the boot command-line can be overridden at boot time.
This is VERY good. But support for override is slipping away from
zSeries Linux.
On Thu, 2004-07-08 at 10:37, Arty Ecock wrote:
> > Something in
> > initrd wants that disk R/W. Adam suggested changing the parmline to
> > something like "DASD=150(ro), ..." but once that is done, you lose the
> > ability to update the basevol root disk (or a copy of it).
On Thu, 8 Jul 2004, Adam Thornton wrote:
> Use multiple parmlines. There's the older Lucius Leland PARM LINE
> stuff, which I really like, which lets you do it very flexibly from CMS,
> and there's also actual official multiboot support in newer s390-tools.
We really need proper support for parm handling.
For those who do not know, VM has long time supported a PARM parm
on the IPL command which effects a 64-byte parm string whether booting
from device or from named saved system (NSS). SAN support breaks it.
So when you're booting Linux on z/VM, you can append parameters,
as long as you're on traditional disk or booting from NSS.
ipl mylinux parm root=/dev/other init=/sbin/blahblah
-or-
ipl 2345 clear parm root=/dev/another mem=1024m
-or-
ipl 1AE clear parm dasd=1AC-1AF root=/dev/dasdc1
You get the idea.
64 bytes is small, but quite sufficient for most overrides.
LOADPARM is another thing, and is seen in the hardware, so you
z/OS folks are more familiar with that one. I don't like LOADPARM.
At only 8 bytes, it doesn't foster entry of arbitrary boot parm text.
The above examples do not fit into LOARPARM space. Any alternate
boot parameters must be pre-set and stamped into a collection.
SAN is good. But the z/VM support for SAN makes "PARM" an
illegal option if the IPL device is SAN. Why is this? But while
SAN support breaks ye olde PARM parm, it supplies a new thing.
IBM calls it SCPDATA, but it looks like an arbitrar buffer
which gets passed to the boot loader. I can't find mention of this
outside of IBM (and SHARE) documentation, so I don't know if it is
architected outside of zSeries. But it's there.
IPL from SAN should pack a PARM string into SCPDATA space,
OR SOMETHING LIKE THAT. There's a lot of value in managed systems
having boot-time overrides containing arbitrary details.
SUMMARY
When booting Linux, there is the concept of a boot parameter line.
We all know and love this as the "parmfile" used by ZIPL, LILO, GRUB.
In many situations, some stage of the bootstrap will allow overrides
to what is stamped on disk. THIS IS A GOOD THING. One such
override is Leland's "vmparm" patch for 2.4.19.
-- R;
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