linux-kernel - RE: [PATCH] blk-mq: export blk_mq_submit

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Date:   Mon, 20 Sep 2021 05:30:14 +0000
From:   Prasad Muppana <Lalita.Muppana@...rosoft.com>
To:     Praveen Kumar <kumarpraveen@...ux.microsoft.com>,
        Christoph Hellwig <hch@...radead.org>
CC:     Chaitanya Kulkarni <chaitanyak@...dia.com>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "schakrabarti@...ux.microsoft.com" <schakrabarti@...ux.microsoft.com>
Subject: RE: [PATCH] blk-mq: export blk_mq_submit_bio symbol

Hi Christoph,

We are in the process of opening the source code for the driver and stuck with this issue which is causing delay in the process. Currently, the Linux customers are impacted by this issue and mostly RHEL8.4 and Ubuntu customers are blocked. So we are looking for any solution that can mitigate this issue as short term goal and in the meantime, we will open the source which will have long term solution to handle this issue. Please help here in this case.

With Thanks,
Prasad 

-----Original Message-----
From: Praveen Kumar <kumarpraveen@...ux.microsoft.com> 
Sent: Monday, September 13, 2021 12:34 PM
To: Christoph Hellwig <hch@...radead.org>
Cc: Chaitanya Kulkarni <chaitanyak@...dia.com>; linux-block@...r.kernel.org; linux-kernel@...r.kernel.org; axboe@...nel.dk; schakrabarti@...ux.microsoft.com; Prasad Muppana <Lalita.Muppana@...rosoft.com>
Subject: Re: [PATCH] blk-mq: export blk_mq_submit_bio symbol

On 13-09-2021 11:39, Christoph Hellwig wrote:
> On Mon, Sep 13, 2021 at 09:54:54AM +0530, Praveen Kumar wrote:
>>>> +EXPORT_SYMBOL_GPL(blk_mq_submit_bio);
>>>>
>>>
>>> Where is the code that used this API ?
>>>
>>
>> Thanks Chaitanya for your response. Please check my response to Christoph.
>> That should give overall understanding of the use-case.
> 
> Which really doesn't matter, while you keep ingoring the relevant 
> question.  If you code is not upstream or at least actively being 
> submitted upstream your questions have no relevance whatsoever.
> If you do not undertand that basic fact your are in the wrong place 
> here.
> 

Hi Christoph,

The upstream activity is being planned and will take sometime to reach to that state as we have to make it ready for latest kernel.

To achieve the same, we were finding some solutions to handle latest changes.
If you have scanned my previous email where I have provided a detail what the driver is doing, I did mention that we plan to use "blk_mq_submit_bio" but failed to do so, as code is not exported. So, to the specific answer, this API is NOT being used anywhere as of now.

However, as you mentioned, the API cannot be exported for any specific driver, is there any solution or way if a custom driver wants to hook the existing bio path and massage it and then fall back to original flow ?

Regards,

~Praveen.