Some senseless babbling from Vitus Jensen to Mike Ruskai
on 10-21-99  20:53 about DosDevIOCtl, cat8, f64...

 VJ> Hello Mike,

 VJ> 19.10.99 07:34, MIKE RUSKAI wrote a message to VITUS JENSEN:

 VJ> ...
 VJ>> ===============================================
 VJ>> DosRead/Write in direct-access mode will normally fail if the
 VJ>> partition is greater than four gigabytes in size.  If you wish
 VJ>> to write an HPFS editor or other tool, you will need to know the
 VJ>> "secret password" that unlocks the big disks.  After you use
 VJ>> DosOpen to get a handle to that volume, use FSCTL FSC_SECTORIO
 VJ>> (0x9014) and in the parameter list, put a pointer to 0xDEADFACE.
 VJ>>  Doing so will put the handle in "sector" mode.  All offsets and
 VJ>> sizes will refer to sectors instead of bytes, allowing you to
 VJ>> address 64Gb.
 VJ>> ================================================= 
 VJ>> From "Undocumented Features of OS/2" (os2undoc.zip, 48K)
 
 MR> Interesting.  I've already figured it out using DosDevIOCtl(),
 MR> though the above might prove useful in the future.
 
 MR> Is that to say that DosSetFilePtr() will also treat parameters as
 MR> sector offsets?

 VJ> Never used that IOCtl.

 VJ> I maintain a file/drive/disk editor to help me develop VRAID.  This
 VJ> editor could switch to sector mode if a disk or drive is larger than
 VJ> 4GB.  Unfortunately I don't own such a disk and all my test disks
 VJ> combined would only reach 3*150+500 = 950MB.  So there is no need to do
 VJ> the coding. 
 VJ> I think you have to try it yourself...

Fido sure it slow...

I did try it, and it works as stated above.  Seemingly any API that works
with file handles will do it one sector at a time.

The drawback, however, is that HPFS386 doesn't seem to support sector I/O.

Now I have to *really* figure DosDevIOCtl() out (primary partitions don't
conform to the assumptions I made).

Mike Ruskai
thannymeister@yahoo.com


... If at first you don't succeed, you must be using Windows.

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