I have a Linux box with 3 ethernet interfaces, eth0, eth1 and eth2.
Am planning to convert the box into a VLAN switch. Let eth1 and eth2 are configured for VLAN 1 and 2 respectively. Let eth0 be a trunk carrying both VLAN frames. Am going for the following configuration.

$vconfig add eth1 1
$vconfig add eth2 2
$
$vconfig add eth0 1
$vconfig add eth0 2
$
$brctl addbr br1
$brctl addif br1 eth0.1
$brctl addif br1 eth1.1
$
$brctl addbr br2
$brctl addif br2 eth0.2
$brctl addif br2 eth1.2

The basic idea of the above configuration is based on the fact that each VLAN can be simulated with individual bridges per VLAN. The above configuration works fine as expected.
eth0 acts as trunk carrying frames with both VLAN IDs(1 and 2). This trunk can be connected to a similar switch on the other end to span the VLAN segmentation across switches.

Now, I wish to make VLAN 1 a native VLAN for VLAN unaware systems connecting to the switch. So, the trunk will carry both tagged frames as well as untagged frames. how to configure such a setup? Also, please give me an idea of how to implement PVIDs?

Thanks!