linux-kernel - Re: [PATCH 1/6] null_blk: allow write zeores on non-membacked

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Message-ID: <41075ae7-6e01-540f-6a68-eac2b9390093@nvidia.com>
Date:   Wed, 5 Oct 2022 18:33:38 +0000
From:   Chaitanya Kulkarni <chaitanyak@...dia.com>
To:     Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "axboe@...nel.dk" <axboe@...nel.dk>,
        "johannes.thumshirn@....com" <johannes.thumshirn@....com>,
        "bvanassche@....org" <bvanassche@....org>,
        "ming.lei@...hat.com" <ming.lei@...hat.com>,
        "shinichiro.kawasaki@....com" <shinichiro.kawasaki@....com>,
        "vincent.fu@...sung.com" <vincent.fu@...sung.com>,
        "yukuai3@...wei.com" <yukuai3@...wei.com>
Subject: Re: [PATCH 1/6] null_blk: allow write zeores on non-membacked

>>> +static bool g_write_zeroes;
>>> +module_param_named(write_zeroes, g_write_zeroes, bool, 0444);
>>> +MODULE_PARM_DESC(write_zeroes, "Support write-zeores operations. Default: false");
>>
>> Why not make this a number of sectors representing the maximum size of a
>> write zero command (blk_queue_max_write_zeroes_sectors()) ? That would
>> allow exercising split write zeros BIOs.
>>
> 
> I kept the implementation identical to the g_discard.
> 
> Perhaps it's time to change it so REQ_OP_DISCARD and
> REQ_OP_WRITE_ZEROES will have same implementation.
> 
> I'll add a discard patch to match your suggested write-zeroes
> behavior.
> 
> -ck
> 

REQ_OP_DISCARD and REQ_OP_WRITE_ZEORES needs to be consistent
when it comes to configuration interface.

I did the change you suggested, it is breaking the backward
compatibility of discard and if we do it only for write-zeroes it
will be inconsistent with the current g_discard behavior.

Let's keep the original behavior and not break the backward
compatibility ?

-ck