Re: Upcoming: Notifications, FS notifications and fsinfo()

[Karel Zak]

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.

I guess your /proc based idea have exactly the same problem... 

I see two possible ways:

- after open("/mnt", O_PATH) create copy-on-write object in kernel to
  represent mount node -- kernel will able to modify it, but userspace
  will get unchanged data from the FD until to close()

- improve fsinfo() to provide set (list) of the attributes by one call

    Karel

-- 
 Karel Zak  <kzak@xxxxxxxxxx>
 http://karelzak.blogspot.com