linux-kernel - Re: [RFC PATCH] ubd: add io_uring based userspace block driver

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Date:   Mon, 9 May 2022 12:13:41 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Gabriel Krisman Bertazi <krisman@...labora.com>,
        Randy Dunlap <rdunlap@...radead.org>
Cc:     Ming Lei <ming.lei@...hat.com>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, io-uring@...r.kernel.org,
        ZiyangZhang <ZiyangZhang@...ux.alibaba.com>,
        Xiaoguang Wang <xiaoguang.wang@...ux.alibaba.com>
Subject: Re: [RFC PATCH] ubd: add io_uring based userspace block driver

On 5/9/22 12:11 PM, Gabriel Krisman Bertazi wrote:
> Randy Dunlap <rdunlap@...radead.org> writes:
> 
>> On 5/9/22 02:23, Ming Lei wrote:
>>> diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig
>>> index fdb81f2794cd..3893ccd82e8a 100644
>>> --- a/drivers/block/Kconfig
>>> +++ b/drivers/block/Kconfig
>>> @@ -408,6 +408,13 @@ config BLK_DEV_RBD
>>>  
>>>  	  If unsure, say N.
>>>  
>>> +config BLK_DEV_USER_BLK_DRV
>>> +	bool "Userspace block driver"
>>> +	select IO_URING
>>> +	default y
>>
>> Any "default y" driver is highly questionable and needs to be justified.
>>
>> Also: why is it bool instead of tristate?
> 
> I think it's only bool because it depends on task_work_add, which is
> not exported to modules.  It is something to be fixed for sure, can
> that function just be exported?

There might (rightfully) be resistance to doing that, as it's one of
this interfaces that's a bit tricky to use correctly and still have it
be efficient and not introduce dependency loops...

But this is very much RFC and in progress stuff, so I don't really think
we need to pay much attention to that at this point.

-- 
Jens Axboe