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Currently, mscc_ocelot ports configure pvid=0 in standalone mode, and inherit the pvid from the bridge when one is present. When the bridge has vlan_filtering=0, the software semantics are that packets should be received regardless of whether there's a pvid configured on the ingress port or not. However, ocelot does not observe those semantics today. Moreover, changing the PVID is also a problem with vlan_filtering=0. We are privately remapping the VID of FDB, MDB entries to the port's PVID when those are VLAN-unaware (i.e. when the VID of these entries comes to us as 0). But we have no logic of adjusting that remapping when the user changes the pvid and vlan_filtering is 0. So stale entries would be left behind, and untagged traffic will stop matching on them. And even if we were to solve that, there's an even bigger problem. If swp0 has pvid 1, and swp1 has pvid 2, and both are under a vlan_filtering=0 bridge, they should be able to forward traffic between one another. However, with ocelot they wouldn't do that. The simplest way of fixing this is to never configure the pvid based on what the bridge is asking for, when vlan_filtering is 0. Only if there was a VLAN that the bridge couldn't mangle, that we could use as pvid.... So, turns out, there's 0 just for that. And for a reason: IEEE 802.1Q-2018, page 247, Table 9-2-Reserved VID values says: The null VID. Indicates that the tag header contains only priority information; no VID is present in the frame. This VID value shall not be configured as a PVID or a member ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ of a VID Set, or configured in any FDB entry, or used in any Management operation. So, aren't we doing exactly what 802.1Q says not to? Well, in a way, but what we're doing here is just driver-level bookkeeping, all for the better. The fact that we're using a pvid of 0 is not observable behavior from the outside world: the network stack does not see the classified VLAN that the switch uses, in vlan_filtering=0 mode. And we're also more consistent with the standalone mode now. And now that we use the pvid of 0 in this mode, there's another advantage: we don't need to perform any VID remapping for FDB and MDB entries either, we can just use the VID of 0 that the bridge is passing to us. The only gotcha is that every time we change the vlan_filtering setting, we need to reapply the pvid (either to 0, or to the value from the bridge). A small side-effect visible in the patch is that ocelot_port_set_pvid needs to be moved above ocelot_port_vlan_filtering, so that it can be called from there without forward-declarations. Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com> Signed-off-by: Jakub Kicinski <kuba@kernel.org> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.