Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley
        Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United
        Kingdom.
        Registered in England and Wales under Company Registration No. 3798903
From:   David Howells <dhowells@redhat.com>
In-Reply-To: <CAHk-=wiMho2AhcTWC3-3zGK7639XL9UT=AheMXY0pxGHDACn6g@mail.gmail.com>
References: <CAHk-=wiMho2AhcTWC3-3zGK7639XL9UT=AheMXY0pxGHDACn6g@mail.gmail.com> <157186182463.3995.13922458878706311997.stgit@warthog.procyon.org.uk> <30394.1571936252@warthog.procyon.org.uk>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     dhowells@redhat.com, Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Nicolas Dichtel <nicolas.dichtel@6wind.com>, raven@themaw.net,
        Christian Brauner <christian@brauner.io>,
        keyrings@vger.kernel.org, linux-usb@vger.kernel.org,
        linux-block <linux-block@vger.kernel.org>,
        LSM List <linux-security-module@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH 11/10] pipe: Add fsync() support [ver #2]
MIME-Version: 1.0
Content-ID: <9190.1571992499.1@warthog.procyon.org.uk>
Date:   Fri, 25 Oct 2019 09:34:59 +0100
Message-ID: <9191.1571992499@warthog.procyon.org.uk>
Content-Type: text/plain; charset=WINDOWS-1252
Content-Transfer-Encoding: quoted-printable
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Linus Torvalds <torvalds@linux-foundation.org> wrote:

> > The keyrings testsuite needs the ability to wait for all the outstandin=
g
> > notifications in the queue to have been processed so that it can then g=
o
> > through them to find out whether the notifications it expected have bee=
n
> > emitted.
>=20
> Can't you just do
>=20
>     ioctl(fd, FIONREAD, &count);
>=20
> in a loop instead? "No paperwork. Just sprinkle some msleep() crack on
> him, and let's get out of here"

Using FIONREAD like this means that I would have to quiesce the tests in or=
der
to sync up.  For the moment that's fine, but at some point I would like to =
be
able to stress test the system by running tests in parallel against the sam=
e
keyring.  Each test needs to check with the monitor whether its keys have
generated the appropriate notifications against a backdrop of events being
continuously generated by other tests.

I can hold this patch for now.  Let me see if I can come up with a better w=
ay
to do it.  Maybe it can be done by dead reckoning, holding up until either
we've counted out a complete ring-full of notifications or read() has come =
up
empty.

David