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From: "Rodney W. Grimes" <rgrimes@gndrsh.aac.dev.com>
Message-Id: <199504190641.XAA01137@gndrsh.aac.dev.com>
Subject: Re: [DEVFS] your opinions sought!
To: julian@freefall.cdrom.com (Julian Elischer)
Date: Tue, 18 Apr 1995 23:41:25 -0700 (PDT)
Cc: fs@freefall.cdrom.com, hackers@freefall.cdrom.com,
        hardware@freefall.cdrom.com
In-Reply-To: <199504190519.WAA06359@freefall.cdrom.com> from "Julian Elischer" at Apr 18, 95 10:19:33 pm
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[Should this really be on 3 lists??? ]
> 
> I am about ready to let people hack at devfs.
> but one thing I'm not sure about:
> 
> what is a good way for the devfs to appear?
> 
> I personally favour something hierachical,
> such as:

I think you are confused about a few things, or at least from looking
at this it leaves me confused:-(.

> 
> /devices/disks/sd0/all
Okay, that is the entire disk.

> /devices/disks/sd0/FAT/all	/* I suppose it could be called C: */
Ah, is that the FAT in slice 0 (DOS would call it partition 0, and it
would *probably* be the C: drive).  Or is this something else?  You
do realize there can be more than 1 primary FAT partition per volume,
though DOS won't grok more than 1 primary active at a time.  

> /devices/disks/sd0/BSD/all
== BSD/c???
And what happens when I have more than 1 BSD slice on a disk (this is
one of the reasons for the slice code after all).

> /devices/disks/sd0/BSD/a
> /devices/disks/sd0/BSD/b
> /devices/disks/sd0/BSD/c
> /devices/disks/sd0/99/all	/* MACH but not recognised */
> /devices/disks/sd0/DOSX/all
> /devices/disks/sd0/DOSX/A
> /devices/disks/sd0/DOSX/B

Is this an extended partition?  If so, extended partitions are not DOS
specific.

> 
> but maybe the following might be as good: (same disk)
> (P=PARTITION, S=SLICE)

I think you have transposed our definitions.  A ``Slice'' is either one of
the 4 primary MBR entries, or 1 of the 26 (is that the right number Bruce?)
logical volumes in an extended MBR entry.  

> 
> /devices/sd0
> /devices/sd0P0
...
> /devices/wd0P0Sa
> 
> 
> Whichever scheme is chosen, I expect a  link (or symlink) from
> /devices/scsi/bus0/targ0/lun0/all->/devices/disks/sd0/all
> or something similar
> e.g.
> /devices/scsi/b0t0l0 -> ../../disks/sd0  (?)
> or
> /devices/scsi/b0t0l0_all hardlink to /devices/sd0  (?)
> /devices/scsi/b0t0l0_P0 hardlink to /devices/sd0P0  (?)
> /devices/scsi/b0t0l0_P1Sa hardlink to /devices/sd0P1Sa  (?)

And who creates these symlinks/hardlinks?  And why do we need them?
How much memory does all this devfs data structure take up?

> remember:
> you can only hardlink devices not directories
> you can symlink anything but it takes a longer lookup sequence.
> (also symlinks are not supported yet)

:-(.


-- 
Rod Grimes                                      rgrimes@gndrsh.aac.dev.com
Accurate Automation Company                   Custom computers for FreeBSD