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

[Jens Axboe]

On 4/8/19 8:54 AM, Paolo Valente wrote:
> 
> 
>> Il giorno 8 apr 2019, alle ore 16:49, Johannes Thumshirn <jthumshirn@xxxxxxx> ha scritto:
>>
>> On Mon, Apr 08, 2019 at 04:39:35PM +0200, Paolo Valente wrote:
>>> From: Angelo Ruocco <angeloruocco90@xxxxxxxxx>
>>>
>>> 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