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From: Wilko Bulte <wilko@yedi.iaf.nl>
Message-Id: <199605301927.VAA08360@yedi.iaf.nl>
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Subject: Re: removing 32 kbyte limit from dump
To: bde@zeta.org.au (Bruce Evans)
Date: Thu, 30 May 1996 21:27:05 +0200 (MET DST)
Cc: freebsd-scsi@FreeBSD.ORG
In-Reply-To: <199605301219.WAA19690@godzilla.zeta.org.au> from "Bruce Evans" at May 30, 96 10:19:02 pm
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As Bruce Evans wrote...
> 
> >But I'm not really satisfied by this. I'd rather see that the st.c
> >driver returns EINVAL or something like that when an attempt is made
> >to write an impossible block size (and of course dump should act 
> >accordingly when it receives the error value).
> 
> 96K is not impossible.  It just gets mutilated to 64K+32K by physio(),

Read impossible as: as the physio() code now handles it.


> and the error isn't detected because both 64K and 32K are possible.
> physio() needs to have a do-not-split flag.

Hm.

> Similar problems probably affect cd and worm devices.  An i/o of
> 100 * 2352 byte blocks would be mutilated at 64K boundaries.  This
> can be fixed using the current physio() interface: don't use rawread()/
> rawwrite(), and provided a minphys() function that returns
> (MAXPHYS / 2352) * 2352 (it must be <= MAXPHYS because physio()
> uses min(MAXPHYS, minphys()).

For cd this is possible not a big problem. I'm not sure about worm.

> >! 			/* so lets tell the user now and not wait for him/her 
> >! 			/* to see the console message */
> >! 			if ( ntrec > 64 ) {
> >! 				msg("Please choose a blocksize <= 64 \n");
> >  				exit(X_ABORT);
> 
> 64 should be MAXPHYS/1024.

True!

Wilko
_     __________________________________________________________________________
 |   / o / /  _   Wilko Bulte             email: wilko@yedi.iaf.nl
 |/|/ / / /( (_)  Private FreeBSD site  - Arnhem - The Netherlands
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