Path: utzoo!attcan!uunet!dino!sharkey!mailrus!tut.cis.ohio-state.edu!killer!elg
From: elg@killer.DALLAS.TX.US (Eric Green)
Newsgroups: comp.sys.amiga.tech
Subject: Re: filesystem links (was: yet another 1.4 request)
Message-ID: <8489@killer.DALLAS.TX.US>
Date: 30 Jun 89 01:11:05 GMT
References: <392@xdos.UUCP>
Organization: The Unix(R) Connection, Dallas, Texas
Lines: 53

From article <392@xdos.UUCP>, by doug@xdos.UUCP (Doug Merritt):
$>Hard links and soft (or symbolic) links are just different
$>implementations of the same idea under UNIX, each with its own
$>strengths and limitations.  Under the Amiga FS in the non-existant
$>v1.4, all links are soft links.  However, UNIX-heads have come to
$>think of soft links as being able to cross file systems, and the FS
$>links under the non-existant v1.4 don't.  So there's some effort to
$>provide a cross-filesystem link "above" FFS, somewhere at the DOS
$>level. 

$ There's a clear need for both hard and soft links, and someone who hasn't
$ used both kinds in the past probably won't clearly understand why, 

The problem is that there is a seperate file system process for each
mounted device on the Amiga, Doug, so it's hard to do cross-device
links (all that DOS is, for the most part, is a converter that turns
your requests into messages to send to the Dos-handler or filesystem).
As for hard links -- in Unix terms, the filename is in the inode under
AmigaDOS. That means you'd have to put the filename somewhere else if
you wanted hard links. That sounds pretty reasonable, actually, if you
stop to think that one of AmigaDOS's biggest problems is pulling up a
directory out of all these scattered "inodes"... unfortunately, the
only DOS routine to pull out filenames from a directory under <=1.3 is
ExNext, which requires one to pull in the complete FIB. Hopefully
that's something that'll be added under later versions of AmigaDOS --
ways of getting filenames out of a directory without pulling in the
entire FIB. 

Needless to say, such a filesystem would be totally different from the
current filesystem, whereas soft links can be plugged into the current
filesystems with little trouble.

$ least Unix V.4 will have a process FS, again an old concept but not one
$ being considered for AmigaDos yet.
  
Are you saying that under Unix V.4 that filesystems run as a process?
That's been true from the earliest versions of AmigaDOS... it's
inherent in the entire system. All that dos.library does is turn your
requests into packets to send (via Exec message-passing) to DOS
handler processes (which may or may not be a file system). See Toebes
& Walker's excellent articles in the last 2 issues of AmiTransactor
for more info.

Of course, under Unix V.4 each filesystem will have only a single
process, while under AmigaDOS each mounted device has a filesystem
process... but I don't want to second-guess the tradeoffs between the
two approaches. 

--
    Eric Lee Green              P.O. Box 92191, Lafayette, LA 70509     
     ..!{ames,decwrl,mit-eddie,osu-cis}!killer!elg     (318)989-9849    
"I have seen or heard 'designer of the 68000' attached to so many names that
 I can only guess that the 68000 was produced by Cecil B. DeMille." -- Bcase