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Mail Archives: djgpp/2002/01/29/05:05:26

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Date: Tue, 29 Jan 2002 12:02:47 +0200 (IST)
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
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To: dom <dcurran AT ti DOT com>
cc: djgpp AT delorie DOT com
Subject: Re: Can't read HDD sectors, why?
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On Mon, 28 Jan 2002, dom wrote:

> How do i go about locking the volume ?

I attach below an excerpt from Ralf Brown's Interrupt List which tells
how to lock and unlock a volume.

> Your right I should have been reading sectors starting from 1, but even if I
> changed this _bios_disk(..) still returned the same errors as before.

I don't think it returned an error, I think you misinterpreted its
return value.  The documentation says that 1 is an error when it is
stored in the _high_ byte of the return value.  A value of 1 has a
zero in its high byte, so _bios_disk actually was telling you it
succeeded.  (The low-byte value of 1 is the number of sectors it
actually read.)

> I also found that calling biosdisk(..) *did* work and I could read sectors.

That's because biosdisk returns only the high byte of the AX register,
while _bios_disk returns the whole AX register.  These two functions
are compatible to different DOS libraries (MSC and Borland), so their
API is a bit different.  Careful reading of the docs should have told
that.


--------D-21440DCX084A-----------------------
INT 21 - MS-DOS 7.0+ - GENERIC IOCTL - LOCK LOGICAL VOLUME
	AX = 440Dh
	CX = 084Ah / 484Ah
	    (category code 08h for FAT12/16, 48h for FAT32; minor code 4Ah)
	BL = drive number (01h=A:,02h=B:,etc)
	BH = lock level (00h-04h)
	DX = drive permissions (see #01575) for Level 1 lock or second
	    Level 0 lock when formatting
Return: CF set on error
	    AX = error code (01h,02h,etc.) (see #01680 at AH=59h/BX=0000h)
	CF clear if successful
Notes:	the logical volume must be locked before direct disk accesses are
	  permitted by Windows95/98
	the commandline LOCK issues a level 4 lock
	Windows98 only permits lock levels 0 and 4
BUG:	Windows98 will return an error (invalid function) if the specified
	  drive number is zero or more than 32, but only allocated 26 bytes
	  for recording locks, so BL=1Bh..20h will trash internal data
	  structures
SeeAlso: AX=440Dh"DOS 3.2+",AX=440Dh/CX=084Bh,AX=440Dh/CX=086Ah
SeeAlso: AX=440Dh/CX=086Ch

Bitfields for drive permissions:
Bit(s)	Description	(Table 01575)
 0	allow writes
 1	disallow new file mappings
 2	volume locked for formatting
--------D-21440DCX084B-----------------------
INT 21 - MS-DOS 7.0+ - GENERIC IOCTL - LOCK PHYSICAL VOLUME
	AX = 440Dh
	CX = 084Bh / 484Bh
	    (category code 08h for FAT12/16, 48h for FAT32; minor code 4Bh)
	BH = logical drive number (00h = default, 01h = A:, etc.)
	BL = lock level (00h-03h)
	DX = drive permissions (see #01575) for Level 1 lock or second
	    Level 0 lock when formatting
Return: CF set on error
	    AX = error code (01h,02h,etc.) (see #01680 at AH=59h/BX=0000h)
	CF clear if successful
Desc:	lock all logical volumes on the same physical volume as the indicated
	  drive
Note:	the physical volume must be locked before direct disk writes via
	  INT 13 are permitted by Windows95
SeeAlso: AX=440Dh"DOS 3.2+",AX=440Dh/CX=084Ah,AX=440Dh/CX=086Bh
SeeAlso: AX=440Dh/CX=086Ch
--------D-21440DCX086A-----------------------
INT 21 - MS-DOS 7.0+ - GENERIC IOCTL - UNLOCK LOGICAL VOLUME
	AX = 440Dh
	CX = 086Ah / 486Ah
	    (category code 08h for FAT12/16, 48h for FAT32; minor code 6Ah)
	BL = drive number (00h=default,01h=A:,etc)
Return: CF set on error
	    AX = error code (01h,02h,etc.) (see #01680 at AH=59h/BX=0000h)
	CF clear if successful
Note:	the logical volume must be locked before direct disk accesses via
	  INT 13 are permitted by Windows95
BUG:	Windows98 will return an error (invalid function) if the specified
	  drive number is zero or more than 32, but only allocated 26 bytes
	  for recording locks, so BL=1Bh..20h will trash internal data
	  structures
SeeAlso: AX=440Dh"DOS 3.2+",AX=440Dh/CX=084Ah,AX=440Dh/CX=086Bh
--------D-21440DCX086B-----------------------
INT 21 - MS-DOS 7.0+ - GENERIC IOCTL - UNLOCK PHYSICAL VOLUME
	AX = 440Dh
	CX = 086Bh / 486Bh
	    (category code 08h for FAT12/16, 48h for FAT32; minor code 6Bh)
	BH = logical drive number (00h = default, 01h = A:, etc.)
Return: CF set on error
	    AX = error code (01h,02h,etc.) (see #01680 at AH=59h/BX=0000h)
	CF clear if successful
Desc:	lock all logical volumes on the same physical volume as the indicated
	  drive
SeeAlso: AX=440Dh"DOS 3.2+",AX=440Dh/CX=084Bh,AX=440Dh/CX=086Ah
--------D-21440DCX086C-----------------------
INT 21 - MS-DOS 7.0+ - GENERIC IOCTL - GET LOCK FLAG STATE
	AX = 440Dh
	CX = 086Ch / 486Ch
	    (category code 08h for FAT12/16, 48h for FAT32; minor code 6Ch)
	BL = drive number (00h=default,01h=A:,etc)
Return: CF set on error
	    AX = error code (01h,02h,etc.) (see #01680 at AH=59h/BX=0000h)
	CF clear if successful
	    AX = access flag (see #01576)
SeeAlso: AX=440Dh"DOS 3.2+",AX=440Dh/CX=084Ah,AX=440Dh/CX=084Bh
SeeAlso: AX=440Dh/CX=0870h

(Table 01576)
Values for drive access flag:
 0000h	no writes/file mappings since last call
 0001h	write operation has occurred since last call
 0002h	file mapping has occurred since last call
Note:	function 6Ch resets the access flag every time it is called

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