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Date:   Sat, 12 Oct 2019 18:38:46 -0400
From:   "Michael S. Tsirkin" <mst@redhat.com>
To:     Stefano Garzarella <sgarzare@redhat.com>
Cc:     netdev@vger.kernel.org, virtualization@lists.linux-foundation.org,
        Jorgen Hansen <jhansen@vmware.com>,
        "David S. Miller" <davem@davemloft.net>,
        Stefan Hajnoczi <stefanha@redhat.com>,
        Adit Ranadive <aditr@vmware.com>,
        Jason Wang <jasowang@redhat.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH net 0/2] vsock: don't allow half-closed socket in the
 host transports
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 <20191011101408-mutt-send-email-mst@kernel.org>
 <20191011143457.4ujt3gg7oxco6gld@steredhat>
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On Fri, Oct 11, 2019 at 04:34:57PM +0200, Stefano Garzarella wrote:
> On Fri, Oct 11, 2019 at 10:19:13AM -0400, Michael S. Tsirkin wrote:
> > On Fri, Oct 11, 2019 at 03:07:56PM +0200, Stefano Garzarella wrote:
> > > We are implementing a test suite for the VSOCK sockets and we discovered
> > > that vmci_transport never allowed half-closed socket on the host side.
> > > 
> > > As Jorgen explained [1] this is due to the implementation of VMCI.
> > > 
> > > Since we want to have the same behaviour across all transports, this
> > > series adds a section in the "Implementation notes" to exaplain this
> > > behaviour, and changes the vhost_transport to behave the same way.
> > > 
> > > [1] https://patchwork.ozlabs.org/cover/847998/#1831400
> > 
> > Half closed sockets are very useful, and lots of
> > applications use tricks to swap a vsock for a tcp socket,
> > which might as a result break.
> 
> Got it!
> 
> > 
> > If VMCI really cares it can implement an ioctl to
> > allow applications to detect that half closed sockets aren't supported.
> > 
> > It does not look like VMCI wants to bother (users do not read
> > kernel implementation notes) so it does not really care.
> > So why do we want to cripple other transports intentionally?
> 
> The main reason is that we are developing the test suite and we noticed
> the miss match. Since we want to make sure that applications behave in
> the same way on different transports, we thought we would solve it that
> way.
> 
> But what you are saying (also in the reply of the patches) is actually
> quite right. Not being publicized, applications do not expect this behavior,
> so please discard this series.
> 
> My problem during the tests, was trying to figure out if half-closed
> sockets were supported or not, so as you say adding an IOCTL or maybe
> better a getsockopt() could solve the problem.
> 
> What do you think?
> 
> Thanks,
> Stefano

Sure, why not.