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Subject: Re: [PATCH 10/18] fsinfo: Provide notification overrun handling
 support [ver #21]
From:   Ian Kent <raven@themaw.net>
To:     Miklos Szeredi <miklos@szeredi.hu>
Cc:     David Howells <dhowells@redhat.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Miklos Szeredi <mszeredi@redhat.com>,
        Christian Brauner <christian@brauner.io>,
        Jann Horn <jannh@google.com>,
        "Darrick J. Wong" <darrick.wong@oracle.com>,
        Karel Zak <kzak@redhat.com>, Jeff Layton <jlayton@redhat.com>,
        Linux API <linux-api@vger.kernel.org>,
        linux-fsdevel@vger.kernel.org,
        LSM <linux-security-module@vger.kernel.org>,
        linux-kernel@vger.kernel.org
Date:   Wed, 05 Aug 2020 19:23:07 +0800
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On Wed, 2020-08-05 at 09:45 +0200, Miklos Szeredi wrote:
> On Wed, Aug 5, 2020 at 4:46 AM Ian Kent <raven@themaw.net> wrote:
> > Coming back to an actual use case.
> > 
> > What I said above is one aspect but, since I'm looking at this
> > right
> > now with systemd, and I do have the legacy code to fall back to,
> > the
> > "just reset everything" suggestion does make sense.
> > 
> > But I'm struggling to see how I can identify notification buffer
> > overrun in libmount, and overrun is just one possibility for lost
> > notifications, so I like the idea that, as a library user, I can
> > work out that I need to take action based on what I have in the
> > notifications themselves.
> 
> Hmm, what's the other possibility for lost notifications?

In user space that is:

Multi-threaded application races, single threaded applications and
signal processing races, other bugs ...

For example systemd has it's own event handling sub-system and handles
half a dozen or so event types of which the mount changes are one. It's
fairly complex so I find myself wondering if I can trust it and
wondering if there are undiscovered bugs in it. The answer to the
former is probably yes but the answer to the later is also probably
yes.

Maybe I just paranoid!
Ian