Re: [Freedos-devel] documentation for FreeDOS filesystem or other programming functions/interfaces?

[Jim M. <jmi...@ya...>]

by size you mean the size of the structure? ouch...  the size of the  structure 
is exactly 0x2c including the reserved stuff.  if you don't  include the 
reserved stuff, it's 0x24.

the first operation should be a calloc to allocate the structure, which zeros 
the structure memory first before the call, and zero the flags (which includes 
CF).
with djgpp, they additionally instruct you to zero sp, and ss, so that go32 will 
automatically alloc a stack (lest you end up with garbage).

with the thinking that if the OS doesn't support this function whatsoever and 
totally blows it, you will get a zero back your original stuff, and of course 
the zeroing of the structure leaves you with the size member coming back with 
what? zero.  thus it is less than 0x24 (the size of the structure minus the 
reserved area) and thus an error.  and of course of it is greater than 0x2c (the 
size of the structure including the reserved space), it is suspect as well.

good catch.

I set CF to 0 before I started, and I got 0 when I ended.  windows xp.  xp 
totally blew the function call.

I set the entire structure to 0's before I started, and I got 0's back.  but 
then again that's windows xp.  it would be interesting to see what happens on 
other OS's...
now I need a guinea pig freedos FAT32 machine to test my df program on...






________________________________
From: dos386 <do...@gm...>
To: fre...@li...
Sent: Mon, February 14, 2011 12:08:20 AM
Subject: Re: [Freedos-devel] documentation for FreeDOS filesystem or other 
programming functions/interfaces?

> RBIL is pretty much it (right?
> http://www.delorie.com/djgpp/doc/rbinter/id/40/32.htm

NO, see above.

> I am hoping to implement some sort of fallback mechanism into the program
> so that if int 21h, 7303h fails, I have int 21h, 36h to fall back on
> but I need to know exactly how to detect failure

See above: clear buffer, set "size" to $30, set flag(C) to 1, call INT
$21 / AX=$7303, if ((flag(C)=1) or ("size" < $24) or ("size">$2C))
then /* F**K, do fallback to AH=$36 */ ...




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