linux-kernel - Re: libata/PATA: GPCMD_SET_STREAMING via SG

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Date:	Thu, 15 Nov 2007 21:55:30 +0100
From:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
To:	Mark Lord <lkml@....ca>
Cc:	Sebastian Kemper <sebastian_ml@....net>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: libata/PATA: GPCMD_SET_STREAMING via SG_IO does nothing


Hi,

On Wednesday 14 November 2007, Mark Lord wrote:
> Sebastian Kemper wrote:
> > Hi Mark!
> > 
> > On Wed, Nov 14, 2007 at 11:41:37AM -0500, Mark Lord wrote:
> >> Ahh.. got it.  The host_status returned (not checked by that code) was 7,
> >> which means "host error".
> >>
> >> In this case, that's because the cmd_len is (16), which is too large for 
> >> ATAPI.
> >> It needs to be changed to (12) instead.
> > 
> > I don't understand. You seem to use a cmd_len of 16 in hdparm yourself.
> ..
> 
> Really?  Where?
> 
> 
> > And why does it work with the "old" ATA driver and not with libata if
> > 16 is too large for ATAPI in general?
> ..
> 
> Now that *is* the question.
> And the answer appears to be that ide-cd.c ignores the passed-in cmd_len,
> and replaces it with:
> 
>    cmd_len = COMMAND_SIZE(rq->cmd[0]);
> 
> That's a SCSI macro to calculate the correct cmd_len based on the SCSI opcode,
> which is very appropriate here.   We should do that too (we don't) in libata.
> 
> But not exactly as IDE does it -- that's actually a bug:  the code needs to also
> check that the new cmd_len is no larger than the original, or we'll get an Oops.
> 
> I'll cook up a patch for that shortly and try it before posting it here.

Could you please also fix ide-cd while at it?

Thanks,
Bart
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