Re: libata passthru: support PIO multi commands

From: Alan Cox
Date: Tue Jun 12 2007 - 06:11:25 EST

> >> + 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.

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