Thank you Jesse for the explanation. That makes sense. -Madhav
On Mon, Aug 1, 2011 at 9:43 PM, Jesse Gross <je...@nicira.com> wrote: > On Mon, Aug 1, 2011 at 1:31 PM, Madhav Puri <madhav.p...@gmail.com> wrote: > > Hello, > > > > I am trying to walk-thru and understand some of the ovs code that gets > > exercised when ovs is configured for user-space datapath (i.e. > > datapath_type=netdev). I have a few questions on use of tap devices in > this > > case for switching data between multiple interfaces. > > > > From the net-device creation function 'netdev_linux_create_tap()', > > definition and the function header, it looks like we open and bind to > same > > tap device (/dev/net/tun) for all interfaces i.e. a read from this device > > could give us data available on any of the underlying bound interfaces. > If > > the understanding is correct, then in 'dpif_netdev_run()' where we > traverse > > the list of all ports and call 'netdev_recv()' we could potentially read > > data on one port which actually came on a different port. Is this > > understanding correct? If so then how do we apply port specific open-flow > > rules in this case? In other words, how do we distinguish between data > > received on one port from another in user-space mode. > > /dev/net/tun is simply a device on which to call ioctls - it is not > the actual tap device. You can create multiple devices with it and > distinguish based on file descriptor. The comment above > netdev_linux_create_tap() refers to opening the same device multiple > times, which will cause users to share buffers but only within that > device. >
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