Date: Tue, 12 Jun 2007 11:16:21 +0100
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Jeff Garzik <jeff@garzik.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: libata passthru: support PIO multi commands
Message-ID: <20070612111621.10074408@the-village.bc.nu>
In-Reply-To: <466DE438.70108@garzik.org>
References: <200706112200.l5BM0qFn005767@hera.kernel.org>
	<20070611233917.4bd8c6d7@the-village.bc.nu>
	<466DE438.70108@garzik.org>
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> >> +		if (multi_count != dev->multi_count)
> >> +			ata_dev_printk(dev, KERN_WARNING,
> >> +				       "invalid multi_count %u ignored\n",
> >> +				       multi_count);
> >> +	}
> > 
> > What limits log spamming here ?
> 
> Intelligence of the user with privs?

Not ever SG_IO call requires priviledges. Not all priviledged users are
so perfect they never make a mistake.

> > Also shouldn't we error this
> > situation not proceed and hope that enough data was supplied not
> > to leave us stuck half way through a command having made a nasty
> > mess on disk ?
> 
> Is that English?  Can you be more specific and more clear?

Issue a multi count sized write. Acidentally collide with another program
which mucks up the multiwrite count (for once it probably won't be HAL
making a mess ;)) and send data. The state of the disk at the point a
short multiwrite terminates is undefined, it may have written some of the
sectors, it may have blanked them all (Optical media) etc. Far better
just to error the invalid command - especially as in some cases without
Mark's fixes for DRQ cleanup on error it may even hang in one direction.

Alan
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