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    SubjectRe: Devices not supporting read-6....
    Hi Alan,
    I'm attaching mail I exchanged with Jens Axboe... apparently, I forgot to
    copy linux-scsi on my response.

    There are other appJens approaches, but Jen's should work Ok.

    Sorry, I don't have his patches.


    Alan Cox wrote:
    > > If you read the SCSI MultiMedia spec, you'll notice 6-byte Read/Write commands
    > > are not mandatory (true for ATAPI & SCSI). So, I'd say the drivers need to be updated.
    > Not the drivers fortunately - just the sd.c code that dispatches commands. If
    > its now allowed then it shouldnt be a blacklist item , it has to get handled
    > properly.
    > Is there a "supports read-10" flag anywhere helpful in the drive data pages ?
    > Alan
    Subject: Re: ten byte writes/reads
    Date: Thu, 02 Dec 1999 16:27:59 -0500
    From: "Robin T. Miller" <>
    Organization: Data Products Group (DPG)
    To: Jens Axboe <>
    References: 1

    Hi All,
    I think it's pretty safe to assume SCSI disks will accept 10-byte Read/Write
    CDB's. In fact, I reviewed several O/S drivers recently, and both NT and SCO
    only use 10 byte CDB's.

    I'm not surprised the 6-byte Write didn't work with your DVD-RAM, since 10-byte
    CDB's are mandatory for Optical and DVD's, byte 6-byte CDB's are optional.

    Sure, reverting to a 6-byte request can be done on Illegal Request sense, but
    unless you have some very old SCSI-1/CCS drives, I'm not sure you'll see a


    Jens Axboe wrote:
    > Hi,
    > After having battled with a DVD-RAM that does not (properly
    > at least) support WRITE_6 for some time, I started looking at
    > the 10/6 byte command logic in sd. It is not clear what the
    > intended effect of the 'ten' flag is.
    > sd_init_onedisk() unconditionally sets the 'ten' flag and
    > requests are queued as READ_10/WRITE_10 if it is set _and_
    > we want to transfer more than 256 blocks or go beyond
    > a block size that fits in the _6 variants.
    > The overhead of using a 10 byte command data block versus
    > the 6 byte equivalent is not worth worrying about IMHO.
    > Therefore I propose the following change to be made:
    > Always use WRITE_10/READ_10 when the 'ten' flag is set.
    > For devices that do not support it, the behaviour will
    > be to reverse to WRITE_6/READ_6 upon the first failed
    > read/write. An alternative solution would be to probe
    > the device in sd_init_onedisk() and set the flag conditionally.
    > Attached patch is against 2.2.14-pre9.
    > --
    > * Jens Axboe <>
    > * Linux CD-ROM Maintainer
    > *
    > --------------------------------------------------------------------------------
    > sd_ten.diffName: sd_ten.diff
    > Type: Plain Text (text/plain)

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