Disk partitioning

[Chris Rende]

Nixdorf Targon M35/50 TOS 3.3 --> Pyramid 9810 OSx 4.0
MP14 disk layout

Background:

I'm confused about how/where/when/why the kernel uses the SIZE parameter
of the partitioning information in /usr/sys/conf/conf.c.

When this machine was installed the vendor changed partition l's entry
in /usr/sys/conf/conf.c (MP14) from 199,262 to 199,409 in order to merge
the 160Mb l and the 90Mb m partitions. Then the vendor ran either MKFS
or NEWFS to create the current 250Mb l partition:

$ ucb df /u1
Filesystem            kbytes    used   avail capacity  Mounted on
/dev/iop/pdisk00l     246150   93228  140614    40%    /u1

(Since /etc/disktab does NOT have the corresponding change I don't think
 that they used NEWFS).

I'm preparing to 'gen a new kernel. I'd like to remove as many of these
"customizations" as possible.

Question:

Can I now change the l entry from 199,409 back to 199,262 without harming
the filesystem or anything else?

My guess is: yes, it can be changed back because of the following:

Rationale:

NEWFS uses the data in /etc/disktab to make the argument list to call MKFS.
NEWFS figures out how many blocks will fit in the target file system and
MKFS creates the file system on the given partition. The size of the new
partition is stored in the filesystem's super-block. Once a filesystem
is created, the values which describe the filesystem's location on disk are:

1) The START parameter from the partition information in the kernel (conf.c)
2) The size parameter from the filesystem's super-block

If the above assumptions are correct then a small 5Mb filesytem can be
built using the 20Mb a partition, and likewise a 180Mb filesystem can be
built accross the m & n partitions using the m partition as a base
(instead of using e).

Actually, the only thing kernel mechanism that I know of that might use the
size paramater (from conf.c) is the swapping routines. Since swap areas or
partitions do not contain filesystems this is the only way for the kernel
to know the size of a given swap partition.

Please correct me if I'm wrong.

Thanks,

car.
-- 
Christopher A. Rende           Central Cartage (Nixdorf/Pyramid/SysVR2/BSD4.3)
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       "I don't ever remember forgetting anything." - Chris Rende