On Tue, Mar 31, 2020 at 07:11:11AM +0200, Miklos Szeredi wrote: > On Mon, Mar 30, 2020 at 11:17 PM Christian Brauner > <christian.brauner@xxxxxxxxxx> wrote: > > > Fwiw, putting down my kernel hat and speaking as someone who maintains > > two container runtimes and various other low-level bits and pieces in > > userspace who'd make heavy use of this stuff I would prefer the fd-based > > fsinfo() approach especially in the light of across namespace > > operations, querying all properties of a mount atomically all-at-once, > > fsinfo(2) doesn't meet the atomically all-at-once requirement. Sure, > it's possible to check the various change counters before and after a > batch of calls to check that the result is consistent. Still, that's > not an atomic all-at-once query, if you'd really require that, than > fsinfo(2) as it currently stands would be inadequate. It at all that's only true for batch requests. > > > and safe delegation through fds. Another heavy user of this would be > > systemd (Cced Lennart who I've discussed this with) which would prefer > > the fd-based approach as well. I think pulling this into a filesystem > > and making userspace parse around in a filesystem tree to query mount > > information is the wrong approach and will get messy pretty quickly > > especially in the face of mount and user namespace interactions and > > various other pitfalls. > > Have you actually looked at my proposed patch? Do you have concrete Yes. So have others, Al actively disliked and nacked it and no-one got excited about it. > issues or just vague bad feelings? We have had that discussion on-list where I made my "vague bad feelings" clear where you responded with the same dismissive style so I don't see the point in repeating this experience. Again, I want to make it clear that here I'm stating my preference as a user of this api and as such I don't want to have to parse through a filesystem to get complex information about filesystems. We've had fruitful discussions [1] around how fsinfo() ties in with supervised mounts and the rest of the mount api and its clear and simple especially in the face of namespaces and implements a nice delegation model. So +1 from me. Christian [1]: https://youtu.be/LN2CUgp8deo?t=6840
