linux-kernel - Re: Upcoming: Notifications, FS notifications and fsinfo()

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Message-ID: <20200406184626.GE2147@fieldses.org>
Date:   Mon, 6 Apr 2020 14:46:26 -0400
From:   "J. Bruce Fields" <bfields@...ldses.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Karel Zak <kzak@...hat.com>,
        Lennart Poettering <mzxreary@...inter.de>,
        Miklos Szeredi <miklos@...redi.hu>,
        Ian Kent <raven@...maw.net>,
        David Howells <dhowells@...hat.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Al Viro <viro@...iv.linux.org.uk>, dray@...hat.com,
        Miklos Szeredi <mszeredi@...hat.com>,
        Steven Whitehouse <swhiteho@...hat.com>,
        Jeff Layton <jlayton@...hat.com>, andres@...razel.de,
        keyrings@...r.kernel.org,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Aleksa Sarai <cyphar@...har.com>
Subject: Re: Upcoming: Notifications, FS notifications and fsinfo()

On Mon, Apr 06, 2020 at 09:34:08AM -0700, Linus Torvalds wrote:
> On Mon, Apr 6, 2020 at 2:17 AM Karel Zak <kzak@...hat.com> 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.

OK, I can't see why that wouldn't work, thanks.

--b.

> 
> 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