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List:       linux-390
Subject:    Read-only DASD and CMSCONFFILE
From:       Philip Rowlands <linux-390 () dimebar ! com>
Date:       2011-02-28 16:42:16
Message-ID: 4D6BD068.3030001 () dimebar ! com
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Short version:

DASD='777,888(ro)'
is valid and useful CMSCONFFILE, but we don't see that syntax in either
the documentation or the script's own output.


Long version:

Picture the scene; there's a minidisk holding kickstart files and the
full RHEL install file set. Other users LINK this minidisk in order to
read the data locally. We configure the target and repo dasd with
DASD=777,888. What happens next?

- The R/O LINK is not detected by the Linux dasd module.
/sys/bus/ccw/devices/0.0.0888/readonly is 0.

- For reasons unclear to me, anaconda wants to write to all the
partition tables it can see, despite having no clearpart, initlabel or
partitions defined for that disk.

- The kernel logs spews out the usual "EXAMINE 24" error and sense hex
data seen when you try to write to a read-only disk.

- anaconda stalls and prompts to Ignore the error on dasdb, unless we're
using non-interactive kickstart, in which case it stalls for good.

How to fix this? The CMSCONFFILE read by linuxrc.s390 (the /sbin/init of
RHEL's initrd installer image) supports a DASD= parameter, which is
sanity-checked and passed to the kernel. Tell linux which minidisks are
readonly like this: DASD=777,888(ro)

If we follow the RHEL install documentation, or rely on linuxrc.s390's
own interactive option "p" to print out the CONF file, we have a
problem. CMSCONFFILE is a shell script, sourced by bash. It must be
written in syntax-compliant bash, which DASD=777,888(ro) is not.

DASD='777,888(ro)' # quoted to protect the parentheses

is correct syntax, and will successfully protect the disk from
anaconda's attempts to write to it.

I'll probably file this in RHEL Bugzilla, and send a note to IBM's Linux
team in Germany, but wanted to post here first for feedback and to see
if anyone else has run into similar problems.


Cheers,
Phil

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