linux-kernel - Re: [PATCH 1/1] block, bfq: delete "bfq" prefix from cgroup filenames

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Date:   Mon, 8 Apr 2019 09:01:18 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Paolo Valente <paolo.valente@...aro.org>,
        Johannes Thumshirn <jthumshirn@...e.de>
Cc:     linux-block <linux-block@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        'Paolo Valente' via bfq-iosched 
        <bfq-iosched@...glegroups.com>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Angelo Ruocco <angeloruocco90@...il.com>,
        lennart@...ttering.net
Subject: Re: [PATCH 1/1] block, bfq: delete "bfq" prefix from cgroup filenames

On 4/8/19 8:54 AM, Paolo Valente wrote:
> 
> 
>> Il giorno 8 apr 2019, alle ore 16:49, Johannes Thumshirn <jthumshirn@...e.de> ha scritto:
>>
>> On Mon, Apr 08, 2019 at 04:39:35PM +0200, Paolo Valente wrote:
>>> From: Angelo Ruocco <angeloruocco90@...il.com>
>>>
>>> When bfq was merged into mainline, there were two I/O schedulers that
>>> implemented the proportional-share policy: bfq for blk-mq and cfq for
>>> legacy blk. bfq's interface files in the blkio/io controller have the
>>> same names as cfq. But the cgroups interface doesn't allow two
>>> entities to use the same name for their files, so for bfq we had to
>>> prepend the "bfq" prefix to each of its files. However no legacy code
>>> uses these modified file names. This naming also causes confusion, as,
>>> e.g., in [1].
>>>
>>> Now cfq has gone with legacy blk, so there is no need any longer for
>>> these prefixes in (the never used) bfq names. In view of this fact, this
>>> commit removes these prefixes, thereby enabling legacy code to truly
>>> use the proportional share policy in blk-mq.
>>>
>>> [1] https://github.com/systemd/systemd/issues/7057
>>
>> Hmm, but isn't this a user-space facing interface and thus some sort of ABI?
>> Do you know what's using it and what breaks due to this conversion?
>>
> 
> Yep, but AFAIK, the problem is exactly the opposite: nobody uses these
> names for the proportional-share policy, or wants to use these names.  I'm
> CCing Lennart too, in case he has some improbable news on this.
> 
> So the idea is to align names to what people expect, possibly before
> more confusion arises.

We can't just rename them since they've already been in a shipped kernel.
The window for doing this passed long ago.

-- 
Jens Axboe