RE: [PATCH] storvsc: workaround for virtual DVD SCSI version

[KY Srinivasan]

> -----Original Message-----
> From: Stephen Hemminger [mailto:stephen@xxxxxxxxxxxxxxxxxx]
> Sent: Tuesday, March 7, 2017 9:16 AM
> To: KY Srinivasan <kys@xxxxxxxxxxxxx>; Haiyang Zhang
> <haiyangz@xxxxxxxxxxxxx>; Long Li <longli@xxxxxxxxxxxxx>;
> martin.petersen@xxxxxxxxxx; hch@xxxxxx; hare@xxxxxxx
> Cc: linux-scsi@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> devel@xxxxxxxxxxxxxxxxxxxxxx; Stephen Hemminger
> <sthemmin@xxxxxxxxxxxxx>
> Subject: [PATCH] storvsc: workaround for virtual DVD SCSI version
> 
> Hyper-V host emulation of SCSI for virtual DVD device reports SCSI
> version 0 (UNKNOWN) but is still capable of supporting REPORTLUN.
> 
> Without this patch, a GEN2 Linux guest on Hyper-V will not boot 4.11
> successfully with virtual DVD ROM device. What happens is that the
> SCSI scan process falls back to doing sequential probing by INQUIRY.
> But the storvsc driver has a previous workaround that masks/blocks all
> errors reports from INQUIRY (or MODE_SENSE) commands.  This workaround
> causes the scan to then populate a full set of bogus LUN's on the
> target and then sends kernel spinning off into a death spiral doing
> block reads on the non-existent LUNs.
> 
> By setting the correct blacklist flags, the target with the
> DVD device is scanned with REPORTLUN and that works correctly.
> 
> Patch needs to go in current 4.11, it is safe but not necessary
> in older kernels.
> 
> Signed-off-by: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>

Reviewed-by: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
> ---
>  drivers/scsi/storvsc_drv.c | 27 +++++++++++++++++----------
>  1 file changed, 17 insertions(+), 10 deletions(-)
> 
> PS: The error handling does need to be fixed (have patches pending)
> but that is interrelated with hotplug and can wait.
> 
> diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
> index 638e5f427c90..19973e874830 100644
> --- a/drivers/scsi/storvsc_drv.c
> +++ b/drivers/scsi/storvsc_drv.c
> @@ -400,8 +400,6 @@
> MODULE_PARM_DESC(storvsc_vcpus_per_sub_channel, "Ratio of VCPUs to
> subchannels")
>   */
>  static int storvsc_timeout = 180;
> 
> -static int msft_blist_flags = BLIST_TRY_VPD_PAGES;
> -
>  #if IS_ENABLED(CONFIG_SCSI_FC_ATTRS)
>  static struct scsi_transport_template *fc_transport_template;
>  #endif
> @@ -1383,6 +1381,22 @@ static int storvsc_do_io(struct hv_device *device,
>  	return ret;
>  }
> 
> +static int storvsc_device_alloc(struct scsi_device *sdevice)
> +{
> +	/*
> +	 * Set blist flag to permit the reading of the VPD pages even when
> +	 * the target may claim SPC-2 compliance. MSFT targets currently
> +	 * claim SPC-2 compliance while they implement post SPC-2 features.
> +	 * With this flag we can correctly handle WRITE_SAME_16 issues.
> +	 *
> +	 * Hypervisor reports SCSI_UNKNOWN type for DVD ROM device but
> +	 * still supports REPORT LUN.
> +	 */
> +	sdevice->sdev_bflags = BLIST_REPORTLUN2 |
> BLIST_TRY_VPD_PAGES;
> +
> +	return 0;
> +}
> +
>  static int storvsc_device_configure(struct scsi_device *sdevice)
>  {
> 
> @@ -1396,14 +1410,6 @@ static int storvsc_device_configure(struct
> scsi_device *sdevice)
>  	sdevice->no_write_same = 1;
> 
>  	/*
> -	 * Add blist flags to permit the reading of the VPD pages even when
> -	 * the target may claim SPC-2 compliance. MSFT targets currently
> -	 * claim SPC-2 compliance while they implement post SPC-2 features.
> -	 * With this patch we can correctly handle WRITE_SAME_16 issues.
> -	 */
> -	sdevice->sdev_bflags |= msft_blist_flags;
> -
> -	/*
>  	 * If the host is WIN8 or WIN8 R2, claim conformance to SPC-3
>  	 * if the device is a MSFT virtual device.  If the host is
>  	 * WIN10 or newer, allow write_same.
> @@ -1661,6 +1667,7 @@ static struct scsi_host_template scsi_driver = {
>  	.eh_host_reset_handler =	storvsc_host_reset_handler,
>  	.proc_name =		"storvsc_host",
>  	.eh_timed_out =		storvsc_eh_timed_out,
> +	.slave_alloc =		storvsc_device_alloc,
>  	.slave_configure =	storvsc_device_configure,
>  	.cmd_per_lun =		255,
>  	.this_id =		-1,
> --
> 2.11.0