Add support for changing network address

[alexandref75]

It is a little simpler than adding a config file.
It adds command line options, allowing changing network configuration.
The defaults are the original values.

[openshift-ci]

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[cfergeau]

It is a little simpler than adding a config file. It adds command line options, allowing changing network configuration. The defaults are the original values.

I’ve finally moved forward with #484 which allows to set network/IP/… using a config file. I’m not opposed to also adding command line options to configure this, but ideally this would be partially automated (--subnetIP 10.0.0.0/8 would automatically set host IP/gateway IP and device IP to valid default values). --subnetIP could be named --subnet or --subnetCIDR

There is code which can help with this in

gvisor-tap-vsock/cmd/gvproxy/config.go

Lines 184 to 197 in dc117b2

	// Parse subnet address for further use
	naddr, err := netip.ParsePrefix(config.Stack.Subnet)
	if err != nil {
	return config, fmt.Errorf("failed to parse subnet: %w", err)
	}
	fuaddr, err := getFirstUsableIPFromSubnet(naddr)
	if err != nil {
	return config, fmt.Errorf("failed to identify first usable address in subnet: %w", err)
	}
	luaddr, err := getLastUsableIPFromSubnet(naddr)
	if err != nil {
	return config, fmt.Errorf("failed to identify last usable address in subnet: %w", err)
	}

, or some alternative API is used here

gvisor-tap-vsock/pkg/services/forwarder/tcp.go

Lines 63 to 67 in dc117b2

	func linkLocal() *tcpip.Subnet {
	_, parsedSubnet, _ := net.ParseCIDR(linkLocalSubnet) // CoreOS VM tries to connect to Amazon EC2 metadata service
	subnet, _ := tcpip.NewSubnet(tcpip.AddrFromSlice(parsedSubnet.IP), tcpip.MaskFromBytes(parsedSubnet.Mask))
	return &subnet
	}