linux-kernel - Re: [PATCH 1/1] s390/dasd: remove ioctl_by

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Date:   Thu, 7 May 2020 17:43:40 +0200
From:   Stefan Haberland <sth@...ux.ibm.com>
To:     Christoph Hellwig <hch@....de>
Cc:     axboe@...nel.dk, linux-block@...r.kernel.org,
        hoeppner@...ux.ibm.com, linux-s390@...r.kernel.org,
        heiko.carstens@...ibm.com, gor@...ux.ibm.com,
        borntraeger@...ibm.com, linux-kernel@...r.kernel.org,
        Peter Oberparleiter <oberpar@...ux.ibm.com>
Subject: Re: [PATCH 1/1] s390/dasd: remove ioctl_by_bdev from DASD driver

Am 07.05.20 um 17:29 schrieb Christoph Hellwig:
> On Thu, May 07, 2020 at 05:22:28PM +0200, Stefan Haberland wrote:
>> OK, just thought again about your suggestion and also that
>> you have already been talking about a symbol lookup I just
>> have written a prototype that took your first two patches
>> as base, exports the symbol of dasd_biodasdinfo and in
>> ibm.c I do a kallsyms_lookup_name("dasd_biodasdinfo").
>>
>> So I would not have to define a structure twice or rely on
>> MAJORs. Also we would not have to define an own file
>> operation only for DASD devices.
>>
>> What do you think about this? If you agree I will polish
>> the patches, test them and send them for review.
> How do you figure out a given gendisk is a DASD device?  I guess
> dasd_biodasdinfo could just check the block_device_operations
> pointer first thing.  That's still a little ugly, but seems the
> least bad idea so far, so please at least post it for discussion.

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.

Will post a patch shortly.