From: jmk@plan9.bell-labs.com
To: 9fans@cse.psu.edu
Subject: Re: [9fans] undocumented fs config options?
Date: Wed, 9 May 2001 00:10:52 -0400 [thread overview]
Message-ID: <20010509041059.A94A6199E7@mail.cse.psu.edu> (raw)
On Tue May 8 11:20:27 EDT 2001, anothy@cosym.net wrote:
> in reading through /sys/src/fs/worms and the file
> server source, there seem to be two undocumented
> device types: r and x.
>
> x is Devswab - i believe this bit-swaps whatever's
> on the physical disk, presumably for moving a file
> system between different-endian servers. correct?
yes, 'x' does the non-trivial swap between big and little
endian filesystem formats. this allowed us to move our old
sony jukeboxes from a big-endian mips magnum to a little-endian
pc. since then we've copied the data off the sonys and
turned them off.
>
> i'm not clear on r; it seems related to be the same
> as w, but for optical disks (described in
> port/portdat.h as "scsi video drive"), or l with no
> label (l is described as "scsi video drive
> (labeled)"). in the examples, r, like l, is only
> used within a j device to describe the unmountable
> platters. it seems either r or l is required in the
> device3 section of a j definition; fsconfig(8)
> makes no mention of that.
my understanding is that 'r' and 'l' only differ in that
with 'l' one block is reserved on the platter for a label.
>
> can l or r be used on regular disks? what's the
> difference between r and w devices?
> -α.
i believe 'r' and 'l' devices can only be used as the third
part of a 'j' device. there is no individual 'init' routine for
'r' and 'l' devices, it's part of the 'j' initialisation.
that's not to say it might be possible to concoct a filesystem
specification with 'r' or 'l' devices not associated with a
jukebox that would pass the configuration parsing, but it wouldn't
work.
next reply other threads:[~2001-05-09 4:10 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-05-09 4:10 jmk [this message]
2001-05-09 7:30 ` Nigel Roles
2001-05-10 5:31 ` Boyd Roberts
-- strict thread matches above, loose matches on Subject: below --
2001-05-10 6:00 nigel
2001-05-10 19:46 ` Boyd Roberts
2001-05-08 15:19 anothy
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