Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!ccut!wnoc-tyo-news!toumon!wucc!ytsuji
From: ytsuji@wucc.waseda.ac.jp (Y.Tsuji)
Newsgroups: comp.sys.atari.st
Subject: Re: Can GCC treat printer like
Summary: file descriptor for raw devices
Message-ID: <5614@wucc.waseda.ac.jp>
Date: 8 May 91 22:13:50 GMT
References: <1912@do.maus.de>
Distribution: world,comp
Organization: The Centre for Informatics, WASEDA Univ.
Lines: 28

It's up to you whether to make use of the TOS Fopen() or not when you
implement your own open() in your own C library. For ordinary files,
the value returned will be similar to what other OS (i.e. unix) expects,
but when it comes to raw devices (/dev/tty,/dev/lpt,/dev/fd0 etc), you
need to be a bit inventive. What I have done is this:
 (1) for keyboard/monitor, parallel port, and RS232C port, the returned
      value by Fopen will be respected but not used. Instead values 128,
      129,130 will be given. (The returned value of fffe etc will be kept
      internally).
 (2) for other devices e.g. disk drives and midi ports, the same trick
     will be applied. drive A will be assigned 256, drive B 257 etc.
     However, as drives are block devices, read/write and lseek can be
     done only in units of 512. And we must keep a file pointer for each
     device. There is no way of knowing the basic features of the device
     as read/write is normally done to disks that are physically formatted
     but may lack boot sector info. I simply followed the nomenclature of
     minix.
      
At any event, I needed a file descriptor table internally that keeps info
to be given to stat() and fstat(). That table also keeps the name of the
file descriptor (I sometimes needed to know the name of the file from the
file descriptor). Read/write of raw device is necessary in such cases as
reformatter(re-initialises the boot sector,FATs and directory) and TAR.

Another thing I needed to use my brain a bit is giving i-node numbers(
real id number of files). I think I better keep this secret to myself so
as not to bore you to death.
Dr Y. Tsuji
ytsuji@cfi.waseda.ac.jp