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

[Linus Torvalds]

On Mon, Apr 6, 2020 at 2:17 AM Karel Zak <kzak@xxxxxxxxxx> wrote:
>
> On Fri, Apr 03, 2020 at 04:30:24PM -0400, J. Bruce Fields wrote:
> >
> > nfs-utils/support/misc/mountpoint.c:check_is_mountpoint() stats the file
> > and ".." and returns true if they have different st_dev or the same
> > st_ino.  Comparing mount ids sounds better.
>
> BTW, this traditional st_dev+st_ino way is not reliable for bind mounts.
> For mountpoint(1) we search the directory in /proc/self/mountinfo.

These days you should probably use openat2() with RESOLVE_NO_XDEV.

No need for any mountinfo or anything like that. Just look up the
pathname and say "don't cross mount-points", and you'll get an error
if it's a mount crossing lookup.

So this kind of thing is _not_ an argument for another kernel querying
interface.  We got a new (and better) model for a lot of this.

              Linus