[3510] in Release_7.7_team
Re: CORRECTION: Odd error from Partition Magic
daemon@ATHENA.MIT.EDU (Greg Hudson)
Thu Sep 19 00:17:39 2002
Date: Thu, 19 Sep 2002 00:17:36 -0400
Message-Id: <200209190417.AAA15418@error-messages.mit.edu>
From: Greg Hudson <ghudson@MIT.EDU>
To: Bill Cattey <wdc@MIT.EDU>
CC: release-team@MIT.EDU, jmhunt@MIT.EDU
In-reply-to: <1030737304.13324.23.camel@tokata.mit.edu>
I think the C/H/S errors are orthogonal to the fatal error, and are
not important. I think they simply represent a mostly-harmless bug in
Bill's version of Partition Magic for the case when a partition's
starting sector cannot be represented in C/H/S form due to field width
restrictions. sfdisk assigns the highest possible C/H/S value in this
case; I'm not sure if Partition Magic would be happy about anything it
could possibly see.
I think sfdisk is generating a partition table which looks like:
1: Windows
2: Maint
3: Extended --> 1: Swap
4: <empty> 2: Extended --> 1: Cache
3: <empty> 2: Extended --> 1: Root
4: <empty> 3: <empty> 2: <empty>
4: <empty> 3: <empty>
4: <empty>
The Linux kernel assigns this partition table device numbers as:
hda1: Windows Partition
hda2: Maintenance Partition
hda3: Extended partition
hda4: <nothing>
hda5: Linux swap partition
hda6: Linux cache partition
hda7: Linux root partition
I think Bill's version of Partition Magic simply can't handle a
partition table like this, so it barfs. I think it's within our
rights to throw up our hands and say that this is an issue between the
user and PowerQuest; it is not of critical importance to us that
Partition Magic works after a Linux-Athena install, as long as it
works beforehand.
However, this new revelation about sfdisk's behavior (and the kernel's
behavior) does mean that we'll need to rethink our installer
partitioning strategy a bit.
---
For the sake of science, here is the evidence which I have and have
not procured in favor of the above theory:
* I verified, by reading /usr/src/linux-*/fs/partitions/msdos.c,
that the Linux kernel assigns hda[1-4] to the primary partitions,
if they exist, whether they are data partitions or extended
partitions; then, for any extended partitions, it assigns
sequentially increasing numbers to logical data partitions found
within the extended partitions or in nested extended partitions
within them.
* The following expert-mode fdisk output came from a laptop in
Bill's possession, which exhibits the Partition Magic errors:
Disk /dev/hda: 240 heads, 63 sectors, 5168 cylinders
Nr AF Hd Sec Cyl Hd Sec Cyl Start Size ID
1 80 1 1 0 239 63 1023 63 37920897 07
2 00 239 63 1023 239 63 1023 75645360 2494800 1c
3 00 239 63 1023 239 63 1023 37920960 37724400 05
4 00 0 0 0 0 0 0 0 0 00
5 00 239 63 1023 239 63 1023 1 1105919 82
6 00 239 63 1023 239 63 1023 1 276479 83
7 80 239 63 1023 239 63 1023 1 36341999 83
Note that the LBA "Start" sector is 1 for each of the logical
partitions. Unless sfdisk created overlapping partitions (which I
think we would have noticed), that implies that each logical
partition lives at the beginning of a distinct extended partition.
* I looked at sfdisk's source code, but didn't find it immediately
easy to understand, so I have not verified that it creates chained
extended partitions.
* I did not examine Bill's laptop's partition table using a tool
other than fdisk in expert mode. However, I can corroborate from
my crash and burn machine, which was also partitioned with sfdisk
via the IS Linux installer (in "wipe the disk" mode):
Disk /dev/hda: 255 heads, 63 sectors, 2431 cylinders
Nr AF Hd Sec Cyl Hd Sec Cyl Start Size ID
1 80 0 2 0 254 63 3 1 64259 83
2 00 0 1 4 254 63 1023 64260 38989755 05
3 00 0 0 0 0 0 0 0 0 00
4 00 0 0 0 0 0 0 0 0 00
5 00 0 2 4 254 63 69 1 1060289 82
6 00 0 2 70 254 63 86 1 273104 83
7 00 0 2 87 254 63 1023 1 37656359 83
Disk /dev/hda: 255 heads, 63 sectors, 2431 cylinders
Units = cylinders of 16065 * 512 bytes
Device Boot Start End Blocks Id System
/dev/hda1 * 1 4 32129+ 83 Linux
/dev/hda2 5 2431 19494877+ 5 Extended
/dev/hda5 5 70 530144+ 82 Linux swap
/dev/hda6 71 87 136552 83 Linux
/dev/hda7 88 2431 18828179+ 83 Linux
Note that the expert-mode listing has the same starting sector for
the three logical partitions, but the standard-mode listing shows
a different starting cylinder for each. (This is kind of
interesting; it's a case where fdisk's expert mode listing doesn't
contain a strict superset of the information in standard mode.)
