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    SubjectRe: [PATCH 1/1] block, bfq: delete "bfq" prefix from cgroup filenames
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    On 4/8/19 9:04 AM, Johannes Thumshirn wrote:
    > [+Cc Michal ]
    > On Mon, Apr 08, 2019 at 04:54:39PM +0200, Paolo Valente wrote:
    >>
    >>
    >>> Il giorno 8 apr 2019, alle ore 16:49, Johannes Thumshirn <jthumshirn@suse.de> ha scritto:
    >>>
    >>> On Mon, Apr 08, 2019 at 04:39:35PM +0200, Paolo Valente wrote:
    >>>> From: Angelo Ruocco <angeloruocco90@gmail.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.
    >
    > OK, crazy idea, not sure if Jens and Tejun will beat me for this, but
    > symlinks?
    >
    > This way we can a) keep the old files and b) have them point to the new (a.k.a
    > cfq style) files.

    I did consider that, and that would be doable. But honestly, I'm having a
    hard time seeing what issue we are attempting to fix by doing this.

    --
    Jens Axboe

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