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Message-ID: <CAJfpegvxKTy+4Zk6banvxQ83PeFV7Xnt2Qv=kkOg57rxFKqVEg@mail.gmail.com>
Date: Wed, 5 Aug 2020 09:43:38 +0200
From: Miklos Szeredi <miklos@...redi.hu>
To: Ian Kent <raven@...maw.net>
Cc: David Howells <dhowells@...hat.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Al Viro <viro@...iv.linux.org.uk>,
Casey Schaufler <casey@...aufler-ca.com>,
Stephen Smalley <sds@...ho.nsa.gov>,
Nicolas Dichtel <nicolas.dichtel@...nd.com>,
Christian Brauner <christian@...uner.io>, andres@...razel.de,
Jeff Layton <jlayton@...hat.com>, dray@...hat.com,
Karel Zak <kzak@...hat.com>, keyrings@...r.kernel.org,
Linux API <linux-api@...r.kernel.org>,
linux-fsdevel@...r.kernel.org,
LSM <linux-security-module@...r.kernel.org>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 13/17] watch_queue: Implement mount topology and attribute
change notifications [ver #5]
On Wed, Aug 5, 2020 at 3:54 AM Ian Kent <raven@...maw.net> wrote:
>
> > > It's way more useful to have these in the notification than
> > > obtainable
> > > via fsinfo() IMHO.
> >
> > What is it useful for?
>
> Only to verify that you have seen all the notifications.
>
> If you have to grab that info with a separate call then the count
> isn't necessarily consistent because other notifications can occur
> while you grab it.
No, no no. The watch queue will signal an overflow, without any
additional overhead for the normal case. If you think of this as a
protocol stack, then the overflow detection happens on the transport
layer, instead of the application layer. The application layer is
responsible for restoring state in case of a transport layer error,
but detection of that error is not the responsibility of the
application layer.
Thanks,
Miklos
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