NetNews Usenet Archive 1993 #3/NN_1993_3.iso/spool/comp/os/linux/24989

Text File | 1993-01-21 | 2.7 KB | 54 lines

Newsgroups: comp.os.linux
Path: sparky!uunet!usc!howland.reston.ans.net!bogus.sura.net!ra!tantalus.nrl.navy.mil!eric
From: [e-mail] (Eric Youngdale)
Subject: Re: SCSI Autodetect? Static table? (Was:
Message-ID: <[e-mail]>
Sender: [e-mail]
Organization: Naval Research Laboratory
References: <[e-mail]>
Date: Thu, 21 Jan 1993 16:10:51 GMT
Lines: 42

In article <[e-mail]> [e-mail] (Craig Anderson) writes:
>In article <[e-mail]> [e-mail] (D
>>Unfortunately, Linux uses a 16 bit dev_t, with only 8 bits reserved
>>for the minor number, which only lets us have 256 minor numbers.
>
>16 bits is enough.  It's bad software engineering to encode attributes
>into the minor number (other than some abstract concept of disk 1,
>disk 2, disk 3).
>
>For a better (tho still quick and dirty) method, how about having a
>table in the kernel (mapping the scsi id, lun, partition, and N bytes
>of device specific stuff to a major/minor number - obviously the generic
>implementation is M+N bytes of device specific stuff with M bytes defined
>for the scsi driver).  Then a simple program could be used to patch
>this table (on disk and/or in mem) in the kernel.  No kernel rebuilds
>required, allows an arbitrary amount of information to be associated with
>each device, is simple to implement and no less efficient at runtime.

    Well, such a table effectively already exists, but it is built up
automatically at boot time, so it never exists on disk.  I am opposed to the
idea of modifying the table in memory because you could easily corrupt a disk
if you started switching around disk ID numbers on the fly.

    I am sympathetic to those who are concerned about device renumbering if
they take a disk out of the system.  How about if we (they) add some symlink
like /dev/scdisk-a0 /dev/scdisk-b1, etc, and have these point at the correct
disks and/or partitions.  If you remove a disk from the system, you can simply
modify the symlinks to point to the new names for the partitions.  Heck, these
could even be automatically generated at boot time in rc.local, so that you do
not have to worry about changing these whenever you add/remove a disk.

    I could add an ioctl that would return the ID and lun for a given scsi
device in order to make it easier to automate the procedure.  How do people
feel about this approach?

-Eric

--
A host is a host from coast to [e-mail]
& no one will talk to a host that's close..........................
Unless the host (that isn't close).................................
is busy, hung or dead................................Eric Youngdale