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Date:	Sat, 17 Mar 2012 11:04:44 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	"K. Y. Srinivasan" <kys@...rosoft.com>
CC:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	devel@...uxdriverproject.org, virtualization@...ts.osdl.org,
	ohering@...e.com, jbottomley@...allels.com, hch@...radead.org,
	linux-scsi@...r.kernel.org
Subject: Re: [PATCH 2/2] Drivers: scsi: storvsc: Don't pass ATA_16 command
 to the host

On 03/16/2012 04:24 PM, K. Y. Srinivasan wrote:
> The current Windows hosts don't handle the ATA_16 command and furthermore
> return a generic error code after filtering the command on the host side.
> For now filter the command on the guest side until the host is modified to
> properly handle unsupported commands.
>
> Signed-off-by: K. Y. Srinivasan<kys@...rosoft.com>
> Reviewed-by: Haiyang Zhang<haiyangz@...rosoft.com>
> ---
>   drivers/scsi/storvsc_drv.c |    9 +++++++++
>   1 files changed, 9 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
> index 8b967c9..783bab8 100644
> --- a/drivers/scsi/storvsc_drv.c
> +++ b/drivers/scsi/storvsc_drv.c
> @@ -1229,8 +1229,17 @@ static bool storvsc_scsi_cmd_ok(struct scsi_cmnd *scmnd)
>   	/*
>   	 * smartd sends this command and the host does not handle
>   	 * this. So, don't send it.
> +	 * The current Windows hosts implement a subset of scsi commands
> +	 * and for the commands that are not implemented, the host filters
> +	 * them and returns a generic failure SRB status. I have been in
> +	 * discussions with the Windows team to return the appropriate SRB
> +	 * status code for unsupported scsi commands and while they have
> +	 * agreed to implement this, it is not clear when this change will be
> +	 * available. Consequently, filtering the command before submitting it
> +	 * to the host is a resonable interim solution.
>   	 */
>   	case SET_WINDOW:
> +	case ATA_16:
>   		scmnd->result = ILLEGAL_REQUEST<<  16;
>   		allowed = false;

It would be even nicer to fill out a nice SCSI status for this.  For an 
illegal request such as this, the libata SCSI simulator 
(drivers/ata/libata-scsi.c) uses a more complete sense buffer setup,

	static void ata_scsi_set_sense(struct scsi_cmnd *cmd, u8 sk,
					u8 asc, u8 ascq)
	{
         cmd->result = (DRIVER_SENSE << 24) | SAM_STAT_CHECK_CONDITION;

         scsi_build_sense_buffer(0, cmd->sense_buffer, sk, asc, ascq);
	}

and calls this function for invalid/unknown/unsupported command ops thusly,

         ata_scsi_set_sense(cmd, ILLEGAL_REQUEST, 0x20, 0x0);
         /* "Invalid command operation code" */

Supplying asc/ascq provides additional information that may be useful in 
determining whether or not to retry, provide better error diagnostics, etc.

The asc/ascq values are found in the SCSI standards documents.

	Jeff


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