linux-kernel - Re: Re: [PATCH 1/2] rbd: RBD_DEV_FLAG_THICK rbd_dev

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Date:   Fri, 23 Mar 2018 10:34:01 +0100
From:   Ilya Dryomov <idryomov@...il.com>
To:     亀井仁志 / KAMEI，HITOSHI 
        <hitoshi.kamei.xm@...achi.com>
Cc:     Dongsheng Yang <dongsheng.yang@...ystack.cn>,
        "sage@...hat.com" <sage@...hat.com>,
        "elder@...nel.org" <elder@...nel.org>,
        "ceph-devel@...r.kernel.org" <ceph-devel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Re: [PATCH 1/2] rbd: RBD_DEV_FLAG_THICK rbd_dev_flags bit

On Fri, Mar 23, 2018 at 10:31 AM, Ilya Dryomov <idryomov@...il.com> wrote:
> On Thu, Mar 22, 2018 at 12:57 PM, 亀井仁志 / KAMEI，HITOSHI
> <hitoshi.kamei.xm@...achi.com> wrote:
>> Hi Yang,
>>
>>> I am not sure is this the best way for this case, what about adding an option in "rbd map -o thick rbd/test"?
>>
>> I will add such option to the rbd map command to manipulate image settings. So, the end-user
>> do not change the settings directly via sysfs file.
>>
>>>       @@ -4011,6 +4012,15 @@ static void rbd_queue_workfn(struct work_struct *work)
>>>                       goto err;
>>>               }
>>>
>>>       +       /* Ignore/skip discard requests for thick-provision image */
>>>
>>> Just ignore? or return -EOPNOTSUPP?
>>
>> Thanks, I think -EOPNOTSUPP is better because user programs cannot know
>> the result of requested operation when the kernel rbd driver ignores
>> discard request. The result of requested operation when the kernel rbd driver
>> ignores discard requests, which probably misleads the user programs.
>>
>>> In addition, we should not ignore the REQ_OP_WRITE_ZEROES.
>>
>> Relating to the above, the return code of REQ_OP_WRITE_ZEROS request
>> is also -EOPNOTSUPP instead of ignoring. I think the result of
>> -EOPNOTSUPP is also better for this request because the kernel
>> rbd driver can expect that user programs write zero data by itself.
>
> REQ_OP_WRITE_ZEROES should continue to work, we just need to make
> sure it never issues truncates or deletes and instead writes zeroes
> explicitly.
>
> I think we should be explicit about the fact that discard is not
> supported instead of accepting the discard request and failing it in
> rbd_queue_workfn().  Attached patch is what I have in mind.

Now with the patch.

Thanks,

                Ilya

View attachment "0001-rbd-notrim-map-option.patch" of type "text/x-patch" (2883 bytes)