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From: portier@dutesta.uucp (Robert Portier)
Newsgroups: comp.unix
Subject: AIX floppy file system layout question.
Message-ID: <1647@mcdchg.UUCP>
Date: Wed, 9-Sep-87 01:43:13 EDT
Article-I.D.: mcdchg.1647
Posted: Wed Sep  9 01:43:13 1987
Date-Received: Fri, 11-Sep-87 01:01:41 EDT
Sender: usenet@mcdchg.UUCP
Organization: Delft University of Technology, Netherlands
Lines: 74
Keywords: IBM PC-RT or is it IBM RT-PC.
Approved: usenet@mcdchg.UUCP

In comp.sys.ibm.pc.rt nobody replied. So I try again in other newsgroups:

Hello out there,

Does anyone know something about the layout of the (AIX) file
system on the floppy of the IBM RT-PC?

We are trying to implement a file system supporting indexed files
on the (high density) floppy drive.

According to the AIX OS Technical Reference the structure of 
the superblock is compatible with the file system of the IBM PC/IX.

The format of the PC/IX-format file sytem superblock as given in
the AIX Operating System Technical Reference (june 3 1986, page 4-76)
is:

typedef struct filsys
{
	ushort	s_isize;	  /* size in blocks of i-list */
	daddr_t	s_fsize;	  /* size in blocks of entire volume */
	short	s_nfree;	  /* number of address in s_free */
	daddr_t s_free[NICFREE];  /* free block list */
	short	s_ninode;	  /* number of inodes in s_inode */
	ino_t	s_inode[NICINOD]; /* free I-node list */
 	char    s_flock;	  /* lock during free list manipulation */
	char    s_ilock;	  /* lock during i-list manipulation */
	char 	s_fmod;		  /* superblock modified flag */
	char    s_ronly;	  /* mounted read-only flag */
	time_t	s_time;		  /* last superblock update */
	short	s_dinfo[4];	  /* device information */
	daddr_t s_tfree;	  /* total free blocks */
	ino_t	s_tinode;	  /* total free i-nodes */
	char	s_fname[6];	  /* file system name */
	char 	s_fpack[6];	  /* file system pack name */
	long 	s_fill[13];	  /* fill out to 512 bytes */
	daddr_t s_swaplo;	  /* start of swap area */
	daddr_t s_nswap;	  /* number of blocks of swap */
	long    s_magic;	  /* magic number of file system */
	long    s_type;		  /* file system type -cluster size */
};
	
#define s_m	s_dinfo[0] 	  /* modulo factor in superblock */
#define s_n	s_dinfo[1]	  /* cylinder size in superblock */
#define s_bsize s_dinfo[2]	  /* block size for this file system */

Mapping block 1 of the floppy (which should be the superblock) on to 
the superblock structure given above and extracting information,
gives us no more information than the file system name and file 
system pack name. Trying to extract other information from the structure
results in *garbage*. 
(While mapping the superblock to the the structure, 
we have taken into account the 8 pad bytes which the compiler adds 
to the structure to align the 4-byte data types.)

Typing the command 'od -dc /dev/fd0 0.' or 'od -dc /dev/rfd0 0.' has lead
us to believe that some of the information that is usually present in the 
superblock, like the file system size and block size, are actually stored
in the bootblock (block 0 on the floppy). 

Are we doing something wrong, or what? Can someone enlighten us.
We appreciate any help.

					Robert & Apoorv.

[non-relevent long quote elided.  -mod]
-- 
###########################################################################
Robert John Portier              |   UUCP:  ..!mcvax!dutrun!dutesta!portier
Delft University of Technology   |
Faculty of Electical Engineering |
Department of Digital Systems    |
and Computer Architecture        |
The Netherlands                  |