Package: e2fsprogs
Version: 1.39+1.40-WIP-2006.11.14+dfsg-2etch1
Severity: wishlist
This is an enhancement request that applies to the s390 and s390x architectures
only. Currently, when mke2fs is run against the single implicit partition of a
CMS minidisk, and the minidisk has been formatted by the CMS FORMAT command
with the RECOMP option, the RECOMP option is ignored and the entire minidisk,
including the RECOMP area, is used for the file system. The RECOMP option is
turned off in the process. The enhancement request is to respect the RECOMP
area and not include it in the filesystem created by mke2fs. The RECOMP flags
in the disk directory should not be altered.
Rationale: Currently, only ECKD DASD devices formatted with the Linux disk
layout (ldl) or the z/OS-compliant compatible disk layout (cdl) are bootable:
ECKD DASD devices formatted with the CMS disk layout are not bootable. But CMS
minidisks formatted with the RECOMP option are potentially bootable under z/VM.
That is how the CMS operating system is booted: from the RECOMP area. zipl
will need to be enhanced also in order to support booting Linux from the RECOMP
area of a CMS minidisk. However, if mke2fs does not respect the RECOMP area
but skates over the top of it, as it does now, such an enhancement to zipl will
be moot. This enhancement request to mke2fs is a prerequisite to the
enhancement request for zipl to support booting from a CMS minidisk. The two
enhancements together would make it possible to implement Linux under z/VM
using only CMS minidisks. This has a number of advantages for z/VM shops, such
as exploitation of existing z/VM DASD
management tools, better exploitation of minidisk caching, etc. Currently, at
least the /boot partition must be cdl or ldl.
(An enhancement to the CMS RESERVE command to respect the RECOMP area might
also be useful, but that is a CMS enhancement request, not a Linux enhancement
request.)
Example:
Assume a minidisk of device type 3390 for 75 cylinders exists at virtual device
number 101. Assume that the CMS operating system is currently running:
format 101 b ( blksize 4096
DMSFOR603R FORMAT WILL ERASE ALL FILES ON DISK B(101). DO YOU WISH TO CONTINUE?
ENTER 1(YES) OR 0(NO).
1
DMSFOR605R ENTER DISK LABEL:
sb0101
DMSFOR733I FORMATTING DISK B
DMSFOR732I 75 CYLINDERS FORMATTED ON B(101)
READY;
format 101 b 74 ( recomp
LABEL VDEV M STAT CYL TYPE BLKSZ FILES BLKS USED-(%) BLKS LEFT BLK TOTAL
SB0101 101 B R/W 74 3390 4096 0 7-00 13313 13320
A CMS file system for a 74-cylinder disk has now been set up, with cylinders
numbered 0-73. The last cylinder, cylinder number 74, which is actually the
75th cylinder, is the RECOMP area. It is reserved for a bootable program. The
RECOMP area is part of the minidisk, but it is not a part of the CMS filesystem
space. CMS is too small for a 1-cylinder RECOMP area. It would need about 7
cylinders or so. But one cylinder is plenty large enough for a boot loader,
such as z/VM's Stand Alone Program Loader (SAPL) or the zipl bootstrap loader
for Linux. In fact, the SAPL can be written to and tested from a CMS minidisk.
Such a minidisk is not bootable by the hardware. I.e., it cannot be IPLed in
an LPAR, even if cylinder 0 of the minidisk corresponds to cylinder 0 of a real
DASD volume. But it can be booted under z/VM by CP.
--
To UNSUBSCRIBE, email to [EMAIL PROTECTED]
with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
