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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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