Path: utzoo!utgpu!water!watmath!clyde!att!pacbell!ames!mailrus!cornell!rochester!udel!mmdf
From: Leisner.Henr@xerox.com (marty)
Newsgroups: comp.os.minix
Subject: Re: Block special file sizes
Message-ID: <3428@louie.udel.EDU>
Date: 22 Jul 88 13:52:14 GMT
Sender: mmdf@udel.EDU
Lines: 44

Andy, you say:
mkfs does it.  It's the only way.  This is the only way FS can tell when end
of file has been hit on a device.

So where does FS get the size?  I had a headache with 1.1 trying to run mkfs on
my hard disk.  Eventually what I did was remove size checks on block special
devices and let the device driver break if it can't seek.  Seems reasonable.  

From my current working version (quasi-protected mode 1.2):
minix/fs/read.c
in read_write()

...
  position = f->filp_pos;
  if (position < (file_pos) 0) return(EINVAL);
  rip = f->filp_ino;
  f_size = rip->i_size;
  r = OK;
  cum_io = 0;
  virg = TRUE;
  mode_word = rip->i_mode & I_TYPE;
#ifdef ORIGINAL
  if (mode_word == I_BLOCK_SPECIAL && f_size == 0) f_size = MAX_P_LONG;
#else
  if(mode_word == I_BLOCK_SPECIAL) f_size = MAX_P_LONG;
#endif


I have no idea where rip->i_size got initialized to something meaningful  for
hard disk partitions, but the number did not make sense.  Off the boot disk , it
certainly wasn't 0.  This fix allowed me to make hard disk partitions on my
genuwine IBM PC AT (I initially thought mkfs was broken but the above code makes
the difference.


What happens is rw_chunk fails eventually when the device driver rejects the
request.


marty
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