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:

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On Tue, Nov 19, 2019 at 12:01:19PM +0100, Stefano Garzarella wrote:

Ideas for long-term changes below.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

Thanks for reviewing!

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diff --git a/MAINTAINERS b/MAINTAINERS
index 760049454a23..c2a3dc3113ba 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS

@@ -17239,6 +17239,7 @@ F:	net/vmw_vsock/diag.c
 F:	net/vmw_vsock/af_vsock_tap.c
 F:	net/vmw_vsock/virtio_transport_common.c
 F:	net/vmw_vsock/virtio_transport.c
+F:	net/vmw_vsock/vsock_loopback.c
 F:	drivers/net/vsockmon.c
 F:	drivers/vhost/vsock.c
 F:	tools/testing/vsock/

At this point you are most active in virtio-vsock and I am reviewing
patches on a best-effort basis.  Feel free to add yourself as
maintainer.

Sure, I'd be happy to maintain it.

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diff --git a/net/vmw_vsock/vsock_loopback.c b/net/vmw_vsock/vsock_loopback.c
new file mode 100644
index 000000000000..3d1c1a88305f
--- /dev/null
+++ b/net/vmw_vsock/vsock_loopback.c

@@ -0,0 +1,217 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * loopback transport for vsock using virtio_transport_common APIs
+ *
+ * Copyright (C) 2013-2019 Red Hat, Inc.
+ * Author: Asias He <asias@redhat.com>
+ *         Stefan Hajnoczi <stefanha@redhat.com>
+ *         Stefano Garzarella <sgarzare@redhat.com>
+ *
+ */
+#include <linux/spinlock.h>
+#include <linux/module.h>
+#include <linux/list.h>
+#include <linux/virtio_vsock.h>

Is it time to rename the generic functionality in
virtio_transport_common.c?  This doesn't have anything to do with virtio
:).

Completely agree, new transports could use it to handle the protocol without
reimplementing things already done.

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+
+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?

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+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?

Thanks,
Stefano