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SubjectRe: "Fix ATAPI transfer lengths" causes CD writing regression
On Wed, Oct 31 2007, Jeff Garzik wrote:
> Jens Axboe wrote:
>> On Wed, Oct 31 2007, Alan Cox wrote:
>>> On Tue, 30 Oct 2007 19:21:29 +0000
>>> Daniel Drake <dsd@gentoo.org> wrote:
>>>
>>>> Alan Cox wrote:
>>>>> I would guess Brasero is issuing a command with the length of data
>>>>> wrongly set. In the old code that might well just produce errors of the
>>>>> "Umm wtf is this data left over for ?", with the new code the drive is
>>>>> likely to change state as it knows the transfer size and that will
>>>>> *correctly* cause an HSM error and what follows.
>>>>>
>>>>> Now the question is who gets the length wrong - Brasero or the ata
>>>>> translation code in libata
>>>> Brasero does exactly the same as my test app which I attached to my last
>>>> mail. Is my test app wrong?
>>> Would need to double check the SCSI specificatons to be sure but I think
>>> you are asking for less data than the drive wishes to provide. You
>>> aren't allowed to do that with ATA.
>> ide-cd handles this by throwing the excess away, which I think is the
>> sane way to do this.
>
> That's easy for the PIO case. But CD writing is normally DMA, which means
> you will get a DMA engine exception if the device wants to give you more
> data than the scatter/gather entries permit.

Right, that's of course problematic... There has to be a way to recover
that situation though, or you can't export any user command issue
facility.

--
Jens Axboe

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