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

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Date:   Thu, 30 Apr 2020 16:02:52 +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
Subject: Re: [PATCH 1/1] s390/dasd: remove ioctl_by_bdev from DASD driver

Am 30.04.20 um 15:13 schrieb Christoph Hellwig:
> On Thu, Apr 30, 2020 at 01:17:54PM +0200, Stefan Haberland wrote:
>> Remove the calls to ioctl_by_bdev from the DASD partition detection code
>> to enable the removal of the specific code.
>>
>> To do so reuse the gendisk private_data pointer and not only provide a
>> pointer to the devmap but provide a new structure containing a pointer
>> to the devmap as well as all required information for the partition
>> detection. This makes it independent from the dasd_information2_t
>> structure.
> I think sharing the data structure in private data is pretty dangerous.

Thought of this as well. This is why I check for the major number before I
use the private pointer to reference the data structure. Thought this would
be enough checking.
Do you think this is not sufficient?

> In the meantime I thought of another idea - the partition code could
> do a symbol_get of a symbol exported by the dasd driver and use that
> to query the information.

Then I would need to export a lot of DASD internal structures to be
available
in thepartition detection code if I would like to walk down our device
map to
findthe corresponding device for example. Not sure if this is that easy.