For one thing the following patchest is supposed to mitigate the regression of extra OGM overhead that we accidentally introduced with the introduction of the compatibility version 15, the TVLV support it provided, together with TT VLAN support. The addition of these TVLVs roughly doubled the OGM overhead back then, also/mainly because the 8021q and Linux bridge modules would add TT VLAN IDs 0 and 1, even if no one is actually using them. While the 8021q VLAN 0 ID addition was addressed in upstream already, PATCH 3/3 tries to avoid unnecessary VLAN additions from the bridge and only adds such VLANs if they were detected on actual traffic.
In preparation of this the internal VLAN creation was overhauled in PATCH 1/3. This also in theory allows detecting new VLAN IDs dynamically from traffic from bridged-in traffic. So far, VLAN IDs could only be used which were anticipated and configured on top of bat0 by the administrator.
However the detection of VLANs from bridged-in clients is by default disabled for now through PATCH 2/3. This patch adds a configurable limit for such snooped VLAN IDs, defaulting to zero for now. The issue is that each added VLAN still increases the OGM size considerably in the current protocol, so it is not advised to add many VLANs at the moment, without a bigger upgrade of the protocol. Also there is still an outstanding issue with temporarily broken broadcast traffic upon adding a new VLAN if BLA is enabled at the same time. Therefore defaulting to zero snooped VLANs from bridged-in clients for now.
Regards, Linus
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v4: * reworking PATCH 3/3: * removing the added exception for VID 0 again, addressed upstream now * replacing the specific VID 1 exception for the bridge default PVID with a more generic solution: a user might change the PVID or add other, untagged VLANs on an access port which we should also ignore; instead always avoid such kernel event additions if a bridge is on top of bat0
v3: * fixing refcounting, removing an unnecessary kref_get() in PATCH 1/3 * adding PATCH 2/3 + PATCH 3/3 * resubmitting without the RFC tag
v2: fix a typo, a missing "to" in the commit message