>> The FAT file system is defined by DOS, and I want UIDE/UIDE2 to
>> have NO run-time "dependencies" on the DOS system.
>
> Nice in theory, but unfortunately doesn't work in practice.

Sure seems to, since before this thread, UIDE/UIDE2 have "trapped" only
BIOS Int 13h I-O requests, and no one has ever complained that it needs
to do anything more!

> DOS's management of the change line is under the sole auspices of the  
> block device driver, not hardware/BIOS (INT 13h).  Since the early 80's,  
> the device drivers built into the DOS kernel for disks with removable  
> media (floppies, removable hard drives) have not solely depended on the  
> BIOS.

Fine for them.   But UIDE/UIDE2 are NOT block-device drivers, and never
will be, since they need NOT be!

> ... If you're caching floppies, but ignoring the DOS device driver and
> just looking at the BIOS, you are out of sync with the OS.

Then why, in fact, has no one ever complained about UIDE/UIDE2 diskette
problems before "VirtualBox"??

I also dispute being "out of sync" with the OS.   On a PC system with NO
"flaky" diskette media-change lines, as I expect they all have been from
1985 on, SO WHAT if the DOS system does a timeout check??   It will find
no change in the diskette UNLESS the user actually DID insert a new one,
in which case the media-change line will also tell UIDE/UIDE2 that a new
diskette is present!   So, where in all that did we get "out of sync"??

> If I'm not mistaken, this is the exact same reason you refuse to support
> removable hard drives with UIDE (you're afraid the BIOS change line might
> be invalid).

You are BADLY MISTAKEN as anyone who read BTTR back in 2010 can tell you!!
I refuse to support "removable" HARD disks as I can't be sure ALL variants
of DOS have the logic to handle a "media-change" for a supposed HARD disk!
Until I am POSITIVE of this, I will NOT have UIDE/UIDE2 "taking the blame"
for any "removable" hard-disk NOT causing the DOS system to flush its disk
buffers if a disk gets changed!!

> Also, to be fair in the particular situation that started this thread,
> this may not actually be the VM's fault ... It could in fact be the VM's 
> fault, but it may not be.

Since all diskettes from 1985 onward have had "change lines", my strong
suspicion is that "VirtualBox" simply is NOT posting a media-change bit
in the BIOS data table, like any real BIOS would do.   That is one more
omission, or "BAD BUG!" if you will, in their "emulation" scheme!!

>> "NO re-entrant calls!", I say again!   Having UIDE/UIDE2 issue
>> an Int 13h of their own WOULD require re-entrancy!
>
> This has been discussed before, also.  With few exceptions, TSR's and  
> device drivers should ALWAYS be re-entrant.  How can you guarantee,  
> e.g., that a software interrupt (such as INT 13h) will never be called  
> from inside a hardware (IRQ) interrupt handler (like INT 08h)?

UIDE/UIDE2 "trap" only Int 13h calls, actually only I-O calls.   Other
Int 13h requests (if any!) are "passed" directly to the BIOS and don't
execute on the UIDE/UIDE2 stack.   My drivers will execute diskette or
non-UltraDMA (or /E disk) I-O requests by "calling the BIOS", but that
needs no re-entrancy, as in such cases the BIOS becomes an "extension"
of UIDE/UIDE2.

So, since UIDE/UIDE2 do "one at a time" I-O requests only (including a
"call the BIOS" I-O request), and as they have NO need to handle other
Int 13h run-time calls, then Why-in-HELL do I need to have re-entrancy
in my drivers??   Bloody waste of time!!

> Granted, an INT 13h call to actually read or write to a disk would not
> (normally) happen from inside an INT 08, but there's no legitimate
> reason it can't check the state of the cache or other similar
> "housekeeping" functions.   You can/should not prevent IRQ handlers
> from calling functions/services provided by your TSR/device driver.
> And if an IRQ handler can do it, there's a possibility of re-entrancy.

And if the user does such a call from an ISR, while my drivers are in
fact still processing a PREVIOUS I-O request, where do I save the ISR
call's variables, where do I get enough stack space to handle TWO (or
maybe more) such re-entrant calls, etc.??

Also, what "check cache status" or "housekeeping" functions have you
found to use in UIDE/UIDE2??   As I follow the "K.I.S.S. Principle",
TAKE A GOOD GUESS how many such functions there are, in UIDE/UIDE2!!

What you suggest as "legitimate" is really DANGEROUS and IS NOT what
most DOS device-drivers have EVER supported, including mine, given a
long-standing DOS convention known as "one at a time I-O"!!


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