From: Stefan Hajnoczi <stefanha@redhat.com>
To: Stefano Garzarella <sgarzare@redhat.com>
Cc: Stefan Hajnoczi <stefanha@gmail.com>,
netdev@vger.kernel.org,
virtualization@lists.linux-foundation.org,
Dexuan Cui <decui@microsoft.com>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
"David S. Miller" <davem@davemloft.net>,
Jorgen Hansen <jhansen@vmware.com>
Subject: Re: [PATCH net-next 4/6] vsock: add vsock_loopback transport
Date: Fri, 22 Nov 2019 09:25:46 +0000 [thread overview]
Message-ID: <20191122092546.GA464656@stefanha-x1.localdomain> (raw)
In-Reply-To: <20191121152517.zfedz6hg6ftcb2ks@steredhat>
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On Thu, Nov 21, 2019 at 04:25:17PM +0100, Stefano Garzarella wrote:
> On Thu, Nov 21, 2019 at 10:59:48AM +0100, Stefano Garzarella wrote:
> > On Thu, Nov 21, 2019 at 09:34:58AM +0000, Stefan Hajnoczi wrote:
> > > On Tue, Nov 19, 2019 at 12:01:19PM +0100, Stefano Garzarella wrote:
> > > > +static struct workqueue_struct *vsock_loopback_workqueue;
> > > > +static struct vsock_loopback *the_vsock_loopback;
> > >
> > > the_vsock_loopback could be a static global variable (not a pointer) and
> > > vsock_loopback_workqueue could also be included in the struct.
> > >
> > > The RCU pointer is really a way to synchronize vsock_loopback_send_pkt()
> > > and vsock_loopback_cancel_pkt() with module exit. There is no other
> > > reason for using a pointer.
> > >
> > > It's cleaner to implement the synchronization once in af_vsock.c (or
> > > virtio_transport_common.c) instead of making each transport do it.
> > > Maybe try_module_get() and related APIs provide the necessary semantics
> > > so that core vsock code can hold the transport module while it's being
> > > used to send/cancel a packet.
> >
> > Right, the module cannot be unloaded until open sockets, so here the
> > synchronization is not needed.
> >
> > The synchronization come from virtio-vsock device that can be
> > hot-unplugged while sockets are still open, but that can't happen here.
> >
> > I will remove the pointers and RCU in the v2.
> >
> > Can I keep your R-b or do you prefer to watch v2 first?
I'd like to review v2.
> > > > +MODULE_ALIAS_NETPROTO(PF_VSOCK);
> > >
> > > Why does this module define the alias for PF_VSOCK? Doesn't another
> > > module already define this alias?
> >
> > It is a way to load this module when PF_VSOCK is starting to be used.
> > MODULE_ALIAS_NETPROTO(PF_VSOCK) is already defined in vmci_transport
> > and hyperv_transport. IIUC it is used for the same reason.
> >
> > In virtio_transport we don't need it because it will be loaded when
> > the PCI device is discovered.
> >
> > Do you think there's a better way?
> > Should I include the vsock_loopback transport directly in af_vsock
> > without creating a new module?
> >
>
> That last thing I said may not be possible:
> I remembered that I tried, but DEPMOD found a cyclic dependency because
> vsock_transport use virtio_transport_common that use vsock, so if I
> include vsock_transport in the vsock module, DEPMOD is not happy.
>
> Do you think it's okay in this case to keep MODULE_ALIAS_NETPROTO(PF_VSOCK)
> or is there a better way?
The reason I asked is because the semantics of duplicate module aliases
aren't clear to me. Do all modules with the same alias get loaded?
Or just the first? Or ...?
Stefan
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next prev parent reply other threads:[~2019-11-22 9:25 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-19 11:01 [PATCH net-next 0/6] vsock: add local transport support Stefano Garzarella
2019-11-19 11:01 ` [PATCH net-next 1/6] vsock/virtio_transport_common: remove unused virtio header includes Stefano Garzarella
2019-11-19 11:01 ` [PATCH net-next 2/6] vsock: add VMADDR_CID_LOCAL definition Stefano Garzarella
2019-11-21 14:49 ` Jorgen Hansen
2019-11-19 11:01 ` [PATCH net-next 3/6] vsock: add local transport support in the vsock core Stefano Garzarella
2019-11-21 15:04 ` Jorgen Hansen
2019-11-21 15:21 ` Stefano Garzarella
2019-11-21 15:53 ` Jorgen Hansen
2019-11-21 16:12 ` Stefano Garzarella
2019-11-21 16:19 ` Jorgen Hansen
2019-11-19 11:01 ` [PATCH net-next 4/6] vsock: add vsock_loopback transport Stefano Garzarella
2019-11-20 1:15 ` David Miller
2019-11-20 9:00 ` Stefano Garzarella
2019-11-21 9:34 ` Stefan Hajnoczi
2019-11-21 9:59 ` Stefano Garzarella
2019-11-21 15:25 ` Stefano Garzarella
2019-11-22 9:25 ` Stefan Hajnoczi [this message]
2019-11-22 10:02 ` Stefano Garzarella
2019-11-19 11:01 ` [PATCH net-next 5/6] vsock: use local transport when it is loaded Stefano Garzarella
2019-11-21 9:46 ` Stefan Hajnoczi
2019-11-21 10:01 ` Stefano Garzarella
2019-11-19 11:01 ` [PATCH net-next 6/6] vsock/virtio: remove loopback handling Stefano Garzarella
2019-11-21 9:46 ` [PATCH net-next 0/6] vsock: add local transport support Stefan Hajnoczi
2019-11-21 10:05 ` Stefano Garzarella
2019-11-21 14:45 ` Jorgen Hansen
2019-11-21 15:13 ` Stefano Garzarella
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