Date: Thu, 26 Jan 1995 09:06:56 -0500 (EST) From: Peter Dufault <dufault@hda.com> To: hsu@fx7.cs.hut.fi Cc: freebsd-hackers@freefall.cdrom.com Subject: Re: kern/189: sd renames disks Message-ID: <199501261406.JAA04537@hda.com> In-Reply-To: <199501260150.RAA10377@freefall.cdrom.com> from "Heikki Suonsivu" at Jan 25, 95 05:50:01 pm
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Heikki Suonsivu writes:
>
>
> >Number: 189
> >Category: kern
> >Synopsis: sd renames disks
> >Confidential: no
> >Severity: serious
(...)
>
> sd thinks it is smarter than you on id's you want your disks have. Install
> three disks, sd1a is /tmp and sd2a is users. Guess what happens if sd1
> breaks down, controller misses it by the phase of the moon, or you forget
> to power it up if it is in an external box.
>
> I wouldn't be happy about editing fstab every time disk configuration changes,
> but that is a minor problem compared to potential dangers this brings us.
>
> (I already complained, but maybe it is a good idea to gnats it so that it
> won't be forgotten)
>
> >How-To-Repeat:
>
Some of this is present in sys/scsi/su.c, but there are a few things
that have to be decided before it is complete.
For example, ID 3 is a fujitsu drive:
> hda.com# ls -lt /dev/rsd2d
> crw-r----- 1 root operator 13, 19 Sep 26 00:01 /dev/rsd2d
> hda.com#
> hda.com# scsi -f /dev/rsd2d -c "12 0 0 0 64 0" -i 64 "s8 z8 z16"
> FUJITSU M2654S-512
and I can access it through a fixed device with the SCSI ID
embedded in the minor number (no, the man page isn't
checked in on how the minor number format):
> hda.com# mknod /dev/scsi/id3 c 18 458755
> hda.com# scsi -f /dev/scsi/id3 -c "12 0 0 0 64 0" -i 64 "s8 z8 z16"
FUJITSU M2654S-512
> hda.com# mknod /dev/scsi/sd/rsd3 c 18 458758
> hda.com# mknod /dev/scsi/sd/sd3 b 18 458758
> hda.com# fsck -n /dev/scsi/sd/rsd3
> ** /dev/scsi/sd/rsd3 (NO WRITE)
> ** Last Mounted on /mnt2
> ** Phase 1 - Check Blocks and Sizes
> ^Chda.com#
However, this does it through the minor numbers and not config.
If you look in scsi/su.c (an unfortunate name that should be changed to
fx.c for "fixed devices" before 2.1) you'll see that you can go from
(BUS,ID,LUN) to
underlying device, so if config is modified to build up a mapping
table then you are almost done.
However, we have to consider the problem of booting an old kernel
and having the same problem Heikki mentions, namely, the new sd0
is scsi id3 or something and we mount on top of it and trash the
disk.
The same problem exists with the multiple host adapters: Currently
they are "counting" host adapters also, and adding a host adapter
with a disk will potentially trash your system.
Some thoughts:
1. Keep the current "auto counting" devices exactly as they are.
2. Add "config'd" devices as a new facility, almost
as Garrett proposed once before except they need new names:
controller scbus0 at aha0
controller scbus1 at ncr0
disk ssd0 at scbus0 target 0 unit 0
disk ssd1 at scbus1 target 0 unit 0
tape sst0 at scbus0 target 5
device sch0 at scbus1 target 4
disk scd0 at scbus1 target 5
These have to be new devconf entries to avoid the "reboot old kernel
and trash your system" problem, and can have new device entry points
such as /dev/scsi/sd and so on.
This will mean there will be three ways to get at a single scsi device:
1. Current "auto counting" devices;
2. Current "fixed" devices with target embedded in the minor number
3. Completely new conf'd devices.
Any thoughts?
P.S.: I use the fixed devices to access my tape drives. I don't mount
my disks on them (mostly because I then can't boot old kernels) and
thus don't consider that facility adequately tested.
Peter
--
Peter Dufault Real Time Machine Control and Simulation
HD Associates, Inc. Voice: 508 433 6936
dufault@hda.com Fax: 508 433 5267
-- Formerly hd@world.std.com. E-mail problems? Tell hdslip@iii.net
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