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Subject: Re: [PATCH] scsi: sd: stop SSD (non-rotational) disks before reboot
To:     Bart Van Assche <bvanassche@acm.org>,
        "James E.J. Bottomley" <jejb@linux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-scsi@vger.kernel.org, linux-doc@vger.kernel.org
References: <499138c8-b6d5-ef4a-2780-4f750ed337d3@0882a8b5-c6c3-11e9-b005-00805fc181fe>
 <b92ce48a-55d8-9377-f6c5-510d7e3beb1b@acm.org>
From:   Simon Arlott <simon@octiron.net>
Message-ID: <04bf3c02-85f4-3fbc-525a-4189aadf9241@0882a8b5-c6c3-11e9-b005-00805fc181fe>
Date:   Wed, 17 Jun 2020 20:32:08 +0100
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On 17/06/2020 20:19, Bart Van Assche wrote:
> On 2020-06-17 11:49, Simon Arlott wrote:
>> @@ -3576,9 +3582,19 @@ static void sd_shutdown(struct device *dev)
>>  		sd_sync_cache(sdkp, NULL);
>>  	}
>>  
>> -	if (system_state != SYSTEM_RESTART && sdkp->device->manage_start_stop) {
>> -		sd_printk(KERN_NOTICE, sdkp, "Stopping disk\n");
>> -		sd_start_stop_device(sdkp, 0);
>> +	if (sdkp->device->manage_start_stop) {
>> +		bool stop_disk = (system_state != SYSTEM_RESTART);
>> +
>> +		if (stop_before_reboot > 1) { /* stop all disks */
>> +			stop_disk = true;
>> +		} else if (stop_before_reboot) { /* non-rotational only */
>> +			stop_disk |= blk_queue_nonrot(sdkp->disk->queue);
>> +		}
>> +
>> +		if (stop_disk) {
>> +			sd_printk(KERN_NOTICE, sdkp, "Stopping disk\n");
>> +			sd_start_stop_device(sdkp, 0);
>> +		}
>>  	}
>>  }
> 
> Is introduction of a new kernel module parameter essential?

It is system-dependent whether or not a reboot is going to result in a
loss of power, so it's required to be able to stop the HDDs too.

They're already always stopped on shutdown where power is definitely
going to be lost. I can't do that by default on a reboot because the
usual convention is that the power stays on during a reboot and it would
be expected that the HDDs keep spinning.

> Or in other
> words, has it been considered to apply the new behavior to all SSDs?

The default value is 1, so it does apply to all SSDs. I want to be able
to configure it to apply to HDDs too.

-- 
Simon Arlott