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From: zambotti@wpowz.enet.dec.com (Walter Zambotti DEC)
Newsgroups: comp.os.os9
Subject: Re: open() + sharable file = no disk
Message-ID: <1991Jun13.014701.22156@tkou02.enet.dec.com>
Date: 13 Jun 91 01:47:01 GMT
References: <1991Jun11.012640.904@tkou02.enet.dec.com> <1656@seq.uncwil.edu> <1991Jun12.012958.10534@tkou02.enet.dec.com> <1991Jun12.051830.4900@ncsu.edu> <1661@seq.uncwil.edu>
Sender: usenet@tkou02.enet.dec.com (USENET News System)
Reply-To: zambotti@wpowz.enet.dec.com (Walter Zambotti DEC)
Organization: Digital Equipment Corporation
Lines: 71

Hi guys,

nothing like a bug to get the blood stiring.  I checked the program on a
floppy and low and behold I found it works ok.    Which confirms what
you have already found out.

I'll patch my /r0 descriptor and recheck the program.

I'm pretty close to finishing the ln(1) command just some debugging to do now!

You wont believe how much checking has to be done in order to create
this link.  Here is a brief overview :

	ln existing_file/dir new_file/dir

	does existing_file exist ?
	does new_file not-exist ?
	are both existing_file and new_file on the same device ? (cant link
across disks!)

	if existing_file is a file then
	 	if existing_file contains a directory path then
			open directory portion of path
		else
			open .
		endif
	else must be directory
		open directory
		read second 32 byte entry (which is .. )
		open ..
	endif

	search for existing_file entry in directory
	extract header sector lsn
	open raw device and read header sector lsn
	extract the link count and bump by one

	don't write back yet

	if new_file contains directory path then
		open directory portion of path
	else
		open .
	endif

	search in directory for empty entry
	if no empty entry then
		seek to end of file+1
	endif

	write new entry with existing_file header sector lsn
	if write succeed then
		write back header sector now
		if write failed then
			erase new entry from directory
		endif
	endif

	done

The current version is quit large about 8k.  It  has every line of code
checked for error conditions which I feel is important until I start to
trust links on OS9.

Links are excellent but if you dont get them wrong it would be easy to
screw up a disk quite quickly.   The moment I get it going I'll release
the source and then start stream lining.

see ya round like a beach ball,

Walter