net: switchdev: remove vid_begin -> vid_end range from VLAN objects

The call path of a switchdev VLAN addition to the bridge looks something
like this today:

        nbp_vlan_init
        |  __br_vlan_set_default_pvid
        |  |                       |
        |  |    br_afspec          |
        |  |        |              |
        |  |        v              |
        |  | br_process_vlan_info  |
        |  |        |              |
        |  |        v              |
        |  |   br_vlan_info        |
        |  |       / \            /
        |  |      /   \          /
        |  |     /     \        /
        |  |    /       \      /
        v  v   v         v    v
      nbp_vlan_add   br_vlan_add ------+
       |              ^      ^ |       |
       |             /       | |       |
       |            /       /  /       |
       \ br_vlan_get_master/  /        v
        \        ^        /  /  br_vlan_add_existing
         \       |       /  /          |
          \      |      /  /          /
           \     |     /  /          /
            \    |    /  /          /
             \   |   /  /          /
              v  |   | v          /
              __vlan_add         /
                 / |            /
                /  |           /
               v   |          /
   __vlan_vid_add  |         /
               \   |        /
                v  v        v
      br_switchdev_port_vlan_add

The ranges UAPI was introduced to the bridge in commit bdced7ef7838
("bridge: support for multiple vlans and vlan ranges in setlink and
dellink requests") (Jan 10 2015). But the VLAN ranges (parsed in br_afspec)
have always been passed one by one, through struct bridge_vlan_info
tmp_vinfo, to br_vlan_info. So the range never went too far in depth.

Then Scott Feldman introduced the switchdev_port_bridge_setlink function
in commit 47f8328bb1a4 ("switchdev: add new switchdev bridge setlink").
That marked the introduction of the SWITCHDEV_OBJ_PORT_VLAN, which made
full use of the range. But switchdev_port_bridge_setlink was called like
this:

br_setlink
-> br_afspec
-> switchdev_port_bridge_setlink

Basically, the switchdev and the bridge code were not tightly integrated.
Then commit 41c498b9359e ("bridge: restore br_setlink back to original")
came, and switchdev drivers were required to implement
.ndo_bridge_setlink = switchdev_port_bridge_setlink for a while.

In the meantime, commits such as 0944d6b5a2fa ("bridge: try switchdev op
first in __vlan_vid_add/del") finally made switchdev penetrate the
br_vlan_info() barrier and start to develop the call path we have today.
But remember, br_vlan_info() still receives VLANs one by one.

Then Arkadi Sharshevsky refactored the switchdev API in 2017 in commit
29ab586c3d83 ("net: switchdev: Remove bridge bypass support from
switchdev") so that drivers would not implement .ndo_bridge_setlink any
longer. The switchdev_port_bridge_setlink also got deleted.
This refactoring removed the parallel bridge_setlink implementation from
switchdev, and left the only switchdev VLAN objects to be the ones
offloaded from __vlan_vid_add (basically RX filtering) and  __vlan_add
(the latter coming from commit 9c86ce2c1ae3 ("net: bridge: Notify about
bridge VLANs")).

That is to say, today the switchdev VLAN object ranges are not used in
the kernel. Refactoring the above call path is a bit complicated, when
the bridge VLAN call path is already a bit complicated.

Let's go off and finish the job of commit 29ab586c3d83 by deleting the
bogus iteration through the VLAN ranges from the drivers. Some aspects
of this feature never made too much sense in the first place. For
example, what is a range of VLANs all having the BRIDGE_VLAN_INFO_PVID
flag supposed to mean, when a port can obviously have a single pvid?
This particular configuration _is_ denied as of commit 6623c60dc28e
("bridge: vlan: enforce no pvid flag in vlan ranges"), but from an API
perspective, the driver still has to play pretend, and only offload the
vlan->vid_end as pvid. And the addition of a switchdev VLAN object can
modify the flags of another, completely unrelated, switchdev VLAN
object! (a VLAN that is PVID will invalidate the PVID flag from whatever
other VLAN had previously been offloaded with switchdev and had that
flag. Yet switchdev never notifies about that change, drivers are
supposed to guess).

Nonetheless, having a VLAN range in the API makes error handling look
scarier than it really is - unwinding on errors and all of that.
When in reality, no one really calls this API with more than one VLAN.
It is all unnecessary complexity.

And despite appearing pretentious (two-phase transactional model and
all), the switchdev API is really sloppy because the VLAN addition and
removal operations are not paired with one another (you can add a VLAN
100 times and delete it just once). The bridge notifies through
switchdev of a VLAN addition not only when the flags of an existing VLAN
change, but also when nothing changes. There are switchdev drivers out
there who don't like adding a VLAN that has already been added, and
those checks don't really belong at driver level. But the fact that the
API contains ranges is yet another factor that prevents this from being
addressed in the future.

Of the existing switchdev pieces of hardware, it appears that only
Mellanox Spectrum supports offloading more than one VLAN at a time,
through mlxsw_sp_port_vlan_set. I have kept that code internal to the
driver, because there is some more bookkeeping that makes use of it, but
I deleted it from the switchdev API. But since the switchdev support for
ranges has already been de facto deleted by a Mellanox employee and
nobody noticed for 4 years, I'm going to assume it's not a biggie.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com> # switchdev and mlxsw
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Kurt Kanzenbach <kurt@linutronix.de> # hellcreek
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 1 insertions, 2 deletions

diff --git a/include/net/switchdev.h b/include/net/switchdev.h
index 99cd538d6519..bac7d3ba574f 100644
--- a/include/net/switchdev.h
+++ b/include/net/switchdev.h
@@ -97,8 +97,7 @@ struct switchdev_obj {
 struct switchdev_obj_port_vlan {
 	struct switchdev_obj obj;
 	u16 flags;
-	u16 vid_begin;
-	u16 vid_end;
+	u16 vid;
 };
 
 #define SWITCHDEV_OBJ_PORT_VLAN(OBJ) \