linux-kernel - Re: [PATCH] block: Add block level changes for inline encryption

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Date:   Fri, 1 Jun 2018 06:27:04 +0000
From:   Ladvine D Almeida <Ladvine.DAlmeida@...opsys.com>
To:     Jens Axboe <axboe@...nel.dk>,
        Ladvine D Almeida <Ladvine.DAlmeida@...opsys.com>,
        "ming.lei@...hat.com" <ming.lei@...hat.com>
CC:     "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Manjunath M Bettegowda" <Manjunath.MB@...opsys.com>,
        Prabu Thangamuthu <Prabu.T@...opsys.com>,
        Tejas Joglekar <Tejas.Joglekar@...opsys.com>,
        "Joao Pinto" <Joao.Pinto@...opsys.com>
Subject: Re: [PATCH] block: Add block level changes for inline encryption

On Thursday 31 May 2018 04:46 PM, Jens Axboe wrote:
> On 5/31/18 1:47 AM, Ladvine D Almeida wrote:
>> On Monday 28 May 2018 04:54 PM, Jens Axboe wrote:
>>> On 5/28/18 7:43 AM, Ladvine D Almeida wrote:
>>>> This patch introduces new variable under bio structure to
>>>> facilitate inline encryption. This variable is used to
>>>> associate I/O requests to crypto information.
>>> Hard no on this, for two reasons:
>>>
>>> 1) Any additions to struct bio are scrutinized heavily and
>>>    need strong justification.
>> Thanks for sharing your feedback on the patch.
>> I am providing reference to an earlier article related to inline encryption support below:
>> https://urldefense.proofpoint.com/v2/url?u=https-3A__lwn.net_Articles_717754_&d=DwICaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=z00zRD9ARrwHpe-XSl1OtUp1uNKGYoXI1G2DhOaDDBI&m=m8U0bg9QiswO2oVJgJKq3MmJpqPPK_tN667XwsjojcM&s=9VPcl80YTKwbf8T-oCxWTRahYzS2xNDHZMexpFbuepY&e=
> Took a quick look, and this looks like a classic case of something
> that should just be a cloned bio. If you clone, you own the bi_private
> field, which is what you need.

Cloning the bio gives ownership of the bi_private variable which i can use to refer to the crypto context.
But i have the following problem here:
1. In the dm-crypt subsystem, we clone the bio and assign the bi_private variable. Afterwards, generic_make_request() is done to submit I/O request to block device.
2. The bio will be cloned further in the below layers. The reference in the bi_private variable is now lost as the bio_clone function will not copy the bi_private variable.

Also, the bi_private variable is already used in the dm-crypt layer for storing its private data. This prevents me from using the same.

>

Thanks,

Ladvine