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    SubjectRe: READ SCSI cmd seems to fail on SATA optical devices...
    On Tue, 2006-11-14 at 11:02 +0900, Tejun Heo wrote:
    > Hello, Mattieu Fluhr.
    > Mathieu Fluhr wrote:
    > > The problem is that, on SATA devices controlled by libata, on some big
    > > files (like for example a 600 MB file) the READ command seems to fail
    > > and outputs garbage (not 1 or 2 bytes diff, but the whole buffer).
    > > -> This problem does not come out everytime, and each time on
    > > different sectors.
    > >
    > > Please note that:
    > > - it is not chipset dependant (tested on nforce4 and sii3114)
    > > - it is not medium or device dependant
    > Hmmm... Interesting. So, you're reading the media by directly issuing
    > commands through the sg interface, right? Can you please try the
    > followings?
    > * Try using /dev/srX or /dev/scdX device instead of /dev/sgX. You can
    > use the command SG_IO but the code path is different, so it will help us
    > rule out sg bug.
    > * Perform rounds of read-verify test using standard block interface (ie.
    > simply opening /dev/srX and reading it).
    I will try this and report the results.

    > [--snip--]
    > > - When I force the bus type to be IDE, our software will then send ATA
    > > commands. In this case, everything works like a charm. No errors at all.
    > What do you mean by 'sending ATA commands'? libata exports all devices
    > as SCSI devices. For ATA devices, you can use ATA passthrough but you
    > send CDBs to ATAPI devices anyway.
    Inside our code, we first guess which the bus type of every device using
    an INQUIRY cmd (0x12).
    - If the device appears to be a SCSI one, then we send "pure" SCSI CDBs
    - For an IDE device, we do, as described in the Annex A of the MMC-5
    spec, and pad each CDBs to 12 bytes.

    So in the case of a READ CDB, we send 10 bytes if the device is a SCSI
    one and 12 for IDE one.

    > Thanks.

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