(P)Dsk functions

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2 total messages Started by scott e garfinkle Mon, 01 Oct 1990 21:20

#1545

Author: scott e garfinkle
Date: Mon, 01 Oct 1990 21:20

22 lines
1417 bytes

Can anybody help me with the functions that directly access disk sectors?
None of the books I have gives a very good description of how to use them.
I need to be able to read and write arbitrary disk sectors.  The OS/2
Programmer's Reference refers to the TRACKLAYOUT structure; but it's
still not clear to me how to use it.  So, the specific questions are:
	1.  How do I set things up so that I read/write a specific
	sector, say the disk's boot sector?

	2.  What are the starting points for the numbering systems?
	(I am guessing that Heads, Cylinder, and FirstSector start at
	zero and SectorNumber starts at 1).

	3.  Is it necessary to do a LOCK[PHYS]DRIVE before any
	read/writes (it would seem so)?

	4.  Is it necessary to fill in the TrackTable array for an
	entire track's worth of sectors?  How much of this array
	*really* has to be filled in?
If there is a reference that explains this that I ought to have, please
feel free to suggest.
	-Scott E. Garfinkle
	Ingres Corp.

Re: (P)Dsk functions

#1546

Author: Jari Artes
Date: Tue, 02 Oct 1990 07:57

39 lines
1813 bytes

seg@ingres.com (scott e garfinkle) writes:

>	1.  How do I set things up so that I read/write a specific
>	sector, say the disk's boot sector?

TRACKLAYOUT is set up as follows:

Command	  db	0	; in this case this could be 1  
Head	  dw	0	; zero based head number
Cylinder  dw	0	; zero based cylinder number
FirstSec  dw	0	; this is zero based INDEX to track table
Sectors	  dw	1	; number of sectors on which to perform the operation
; this is the track table
; first (and last) entry:
SecNum	  dw	1	; one based physical sector number
SecSize	  dw	512	; sector size

>	2.  What are the starting points for the numbering systems?
>	(I am guessing that Heads, Cylinder, and FirstSector start at
>	zero and SectorNumber starts at 1).

Your assumptions are correct.

>	3.  Is it necessary to do a LOCK[PHYS]DRIVE before any
>	read/writes (it would seem so)?

Not necessarily in case you just read partition tables, boot records  
or other data that is not subject to change during your program's lifetime.
It is a good practice to lock the drive(s) you're operating on, but
make sure your program doesn't crash before the lock is released.

>	4.  Is it necessary to fill in the TrackTable array for an
>	entire track's worth of sectors?  How much of this array
>	*really* has to be filled in?

There must be cSectors elements in the array.

--
Jari Artes  jaria@tuura.yj.data.nokia.fi

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