1. Feature Overview:
Feature Id: [60872]
a. Name of Feature: [5.6 FEAT] cio_ignore usage with installer, boot and tools (AKA: cio_ignore
entry in generic.prm for LPARs)
b. Feature Description
Currently customers are complaining that when lots of devices are visible to a Linux on System z
system, although not all these devices are in use, they consume precious resources and time, during
installation, boot process and normal work, in case of a device recovery situation, for example when
uCode in the machine or storage is updated or a HW card is changed on the fly.

We would like Red Hat to avoid this resources and performance issue and document which implication
has for the user during
(1) installation,
(2) boot and
(3) normal work
by making use of the cio_ignore kernel parameter to mask/unmask selected devices and the capability
to mask/unmask selected devices on the fly using the proc interface.
For documentation about this kernel parameter and proc interface please read:
http://www.ibm.com/developerworks/linux/linux390/october2005_documentation.html
Device Drivers, Features, and Commands - SC33-8289-04
Chapter 33, pages 405-407

Even more details:
A Linux on System z system will in most cases see a lot more devices than it should be using (up to
a current theoretical maximum of 262144 devices, in practice, 1000-4000 devices are common) Using
the cio_ignore kernel parameter and /proc interface, this feature should mask the ccw devices which
are not used and unmask them if they are needed. Note: When unmasking should be waited/verified that
dev. is there (via sysfs) with a timeout (in case device does not exist).

This should be done during the installation and HW setup tools (like
system-config-network) and persistent for each boot.

What is needed for this feature:
- Patch anaconda to: By default mask all the devices except the console (0009) in generic.prm
(default parmfile for installation)and propagate this kernel parameter to the zipl.conf (for boot)
Unmask and wait for appearance of devices needed (interactive and kickstart)[linuxrc.s390 already
has support; backport for zfcp in anaconda]
- Patch mkinitrd (for root devices only) / initscripts (for all other devices)
to: Unmask and wait for appearance of devices needed which are enumerated in already existing config
files such as modprobe.conf (options dasd_mod dasd=...), zfcp.conf (1st column) and ifcfg-*
(SUBCHANNELS=...) where device numbers are listed (doing so automatically handles all cases of
device configuration during installation, post-installation or manual editing of config files)
- Patch device configuration tools (at this moment only system-config-network) to: Unmask and wait
for appearance of devices as needed during user-interactive configuration


2. Feature Details:
Sponsor: ---
Architectures:
  zSeries - 64 native

Arch Specificity: purely arch specific code
Affects Kernel Modules: No
Delivery Mechanism: LDP Deliverable
Category: other
Request Type: Installer - Enhancement from Distributor
d. Upstream Acceptance: Accepted
Sponsor Priority P1
f. Severity: ship issue
IBM Confidential: No
Code Contribution: no
g. Component Version Target:
---

3. Business Case
Allow customers to Install Linux on an LPAR configured to have potential access to a huge number of
devices, without having the performance impacts suffering right now.


4. Primary contact at Red Hat:
John Jarvis
jjarvis

5. Primary contacts at Partner:
Project Management Contact:
Hans-Georg Markgraf, mgrf.com

Technical contact(s):
Gonzalo Muelas Serrano, gmuelas.com