Re: [RFC 09/10] scsi: sd: Avoid sending medium write commands if device is write protected

[Christoph Hellwig <hch@infradead.org>]

This looks reasonable to me.  Martin, and objections?

On Mon, Aug 11, 2014 at 03:40:37PM +0300, Dolev Raviv wrote:
> From: Sujit Reddy Thumma <sthumma@codeaurora.org>
> 
> The SYNCHRONIZE_CACHE command is a medium write command and hence can
> fail when the device is write protected. Avoid sending such commands by
> making sure that write-cache-enable is disabled even though the device
> claim to support it.
> 
> Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>
> Signed-off-by: Dolev Raviv <draviv@codeaurora.org>
> 
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index 3663e38..67282bf 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -185,7 +185,7 @@ cache_type_store(struct device *dev, struct device_attribute *attr,
>  	if (ct < 0)
>  		return -EINVAL;
>  	rcd = ct & 0x01 ? 1 : 0;
> -	wce = ct & 0x02 ? 1 : 0;
> +	wce = (ct & 0x02) && !sdkp->write_prot ? 1 : 0;
>  
>  	if (sdkp->cache_override) {
>  		sdkp->WCE = wce;
> @@ -2493,6 +2493,10 @@ sd_read_cache_type(struct scsi_disk *sdkp, unsigned char *buffer)
>  			sdkp->DPOFUA = 0;
>  		}
>  
> +		/* No cache flush allowed for write protected devices */
> +		if (sdkp->WCE && sdkp->write_prot)
> +			sdkp->WCE = 0;
> +
>  		if (sdkp->first_scan || old_wce != sdkp->WCE ||
>  		    old_rcd != sdkp->RCD || old_dpofua != sdkp->DPOFUA)
>  			sd_printk(KERN_NOTICE, sdkp,
> -- 
> 1.8.5.2
> -- 
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