linux-kernel - Re: [PATCH 2/2] Drivers: scsi: storvsc: Don't pass ATA

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Date:	Sat, 17 Mar 2012 19:55:40 +0100
From:	Douglas Gilbert <dgilbert@...erlog.com>
To:	Jeff Garzik <jeff@...zik.org>
CC:	"K. Y. Srinivasan" <kys@...rosoft.com>, 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 12-03-17 04:04 PM, Jeff Garzik wrote:
> 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,
I agree with your suggestion and would point out that the
originally proposed:
     scmnd->result = ILLEGAL_REQUEST<<  16;

is just plain wrong. result[23:16] is a Linux invented host byte
code (they typically start with "DID_") while ILLEGAL_REQUEST is
a SCSI sense key.

Doug Gilbert

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