On Mon, Apr 11, 2016 at 03:54:08PM +0300, Michael S. Tsirkin wrote: > On Mon, Apr 11, 2016 at 11:45:48AM +0100, Stefan Hajnoczi wrote: > > On Fri, Apr 08, 2016 at 04:35:05PM +0100, Ian Campbell wrote: > > > On Fri, 2016-04-01 at 15:23 +0100, Stefan Hajnoczi wrote: > > > > This series is based on Michael Tsirkin's vhost branch (v4.5-rc6). > > > > > > > > I'm about to process Claudio Imbrenda's locking fixes for virtio-vsock but > > > > first I want to share the latest version of the code. Several people are > > > > playing with vsock now so sharing the latest code should avoid duplicate work. > > > > > > Thanks for this, I've been using it in my project and it mostly seems > > > fine. > > > > > > One wrinkle I came across, which I'm not sure if it is by design or a > > > problem is that I can see this sequence coming from the guest (with > > > other activity in between): > > > > > > 1) OP_SHUTDOWN w/ flags == SHUTDOWN_RX > > > 2) OP_SHUTDOWN w/ flags == SHUTDOWN_TX > > > 3) OP_SHUTDOWN w/ flags == SHUTDOWN_TX|SHUTDOWN_RX How did you trigger this sequence? I'd like to reproduce it. > > > I orignally had my backend close things down at #2, however this meant > > > that when #3 arrived it was for a non-existent socket (or, worse, an > > > active one if the ports got reused). I checked v5 of the spec > > > proposal[0] which says: > > > If these bits are set and there are no more virtqueue buffers > > > pending the socket is disconnected. > > > > > > but I'm not entirely sure if this behaviour contradicts this or not > > > (the bits have both been set at #2, but not at the same time). > > > > > > BTW, how does one tell if there are no more virtqueue buffers pending > > > or not while processing the op? > > > > #2 is odd. The shutdown bits are sticky so they cannot be cleared once > > set. I would have expected just #1 and #3. The behavior you observe > > look like a bug. > > > > The spec text does not convey the meaning of OP_SHUTDOWN well. > > OP_SHUTDOWN SHUTDOWN_TX|SHUTDOWN_RX means no further rx/tx is possible > > for this connection. "there are no more virtqueue buffers pending the > > socket" really means that this isn't an immediate close from the > > perspective of the application. If the application still has unread rx > > buffers then the socket stays readable until the rx data has been fully > > read. > > Yes but you also wrote: > If these bits are set and there are no more virtqueue buffers > pending the socket is disconnected. > > how does remote know that there are no buffers pending and so it's safe > to reuse the same source/destination address now? Maybe destination > should send RST at that point? You are right, the source/destination address could be reused while the remote still has the connection in their table. Connection establishment would fail with a RST reply. I can think of two solutions: 1. Implementations must remove connections from their table as soon as SHUTDOWN_TX|SHUTDOWN_RX is received. This way the source/destination address tuple can be reused immediately, i.e. new connections with the same source/destination would be possible while an application is still draining the receive buffers of an old connection. 2. Extend the connection lifecycle so that an A->B SHUTDOWN_TX|SHUTDOWN_RX must be followed by a by a B->A RST to close a connection. This way the source/destination address is only in use once at a time. Option #2 seems safer because there is no overlap in source/destination address usage.
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