On Mon, 8 Apr 2019 at 17:05, Jens Axboe <axboe@xxxxxxxxx> wrote: > > 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@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. > > > > 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, didn't we actually break userspace ABI when dropping the legacy block code and its I/O schedulers? So, to me, it seems like introducing symlinks as suggested above, would actually fix this "regression", wouldn't it? Kind regards Uffe
