Stefan Hajnoczi <stefanha@xxxxxxxxxxxxxxxxxx> writes: > On Thu, May 24, 2012 at 05:53:21PM -0300, Luiz Capitulino wrote: >> On Fri, 25 May 2012 01:59:06 +0800 >> zwu.kernel@xxxxxxxxx wrote: >> >> > From: Zhi Yong Wu <wuzhy@xxxxxxxxxxxxxxxxxx> >> > >> > The patchset implements network hub stead of vlan. The main work was done by stefan, and i rebased it to latest QEMU upstream, did some testings and am responsible for pushing it to QEMU upstream. >> >> Honest question: does it really pay off to have this in qemu vs. using one of >> the externaly available solutions? > > For typical KVM setups this feature will be unused. > > However, the legacy QEMU "vlan" feature does have a few uses: > > 1. It's how the "dump" netdev can be connected up with a guest NIC and > host netdev. Create a hub, attach the guest NIC, attach the host > netdev, and attach the dump netdev. This allows the dump netdev to > see all traffic. > > 2. It lets you build virtual network segments. Several point-to-point > connections can be brought together. Start 3 VMs connected by the > "socket" netdev and have one of them use a hub. This may be > inefficient but I wouldn't be surprised if there are people out there > doing this. Those people will find other, superior ways to do this once this inefficient way is gone. We'd do them a favour, I'd say ;) > The point of this patch series is to remove the special-case net.c code > for the legacy "vlan" feature. Today's code makes it harder to > implement a clean QOM model and is a burden for the net subsystem in > general. This series takes the vlan functionality and puts it into a > normal netdev - it extracts the feature from net.c. Welcome improvement, but... > (If we didn't care about backwards compatibility we could just drop > vlans completely and rewrite the "dump" netdev to hook into the net.h > API somehow.) ... is backward compatiblity really worth the extra net client? Please excuse my ignorant question (I haven't studied the series): what kind of backward compatiblity exactly do we get here? Command line: -net option vlan still works? Or just semantic: whatever you could do with vlans you can now do with hubs? In case it's the latter: well, whatever you could do with vlans you can already do with external software, can't you? Why is it worthwhile to provide yet another way within QEMU? -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
