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Date:   Thu, 7 May 2020 17:45:54 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Stefan Haberland <sth@linux.ibm.com>
Cc:     Christoph Hellwig <hch@lst.de>, axboe@kernel.dk,
        linux-block@vger.kernel.org, hoeppner@linux.ibm.com,
        linux-s390@vger.kernel.org, heiko.carstens@de.ibm.com,
        gor@linux.ibm.com, borntraeger@de.ibm.com,
        linux-kernel@vger.kernel.org,
        Peter Oberparleiter <oberpar@linux.ibm.com>
Subject: Re: [PATCH 1/1] s390/dasd: remove ioctl_by_bdev from DASD driver
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On Thu, May 07, 2020 at 05:43:40PM +0200, Stefan Haberland wrote:
> Not checked till now. I just was thinking about the basicapproach.
> 
> I could either check the block_device_operations like you suggested
> or I could verify that the gendisk pointer is already in our devmap
> and therefor belongs to the DASD driver.

The ops pointer check is simpler and cheaper, so I'd suggest that.