Hi Johannes,

Thanks for reviewing.

On Wed, May 9, 2012 at 2:15 AM, Johannes Berg [off-list ref] wrote:

On Thu, 2012-04-26 at 15:28 -0700, Thomas Pedersen wrote:

quoted

It seems as long as we have a netdev, a wdev is available as well.
Remove the restriction that netdev must be up before a wdev can be
obtained in nl80211, or changing channels in cfg80211.

Signed-off-by: Thomas Pedersen <redacted>

---
Hi list,

This was encountered while implementing an interface for setting
BSSBasicRateSet in mesh. The wdev->channel is needed in nl80211.c for
rate verification, but prior to this patch not available.  This doesn't
seem right since the following sequence of commands would fail:

iw wlan0 set type mp
iw wlan0 set channel n
ip link set wlan0 up
iw wlan0 mesh join meshid basic-rate 1,2

Also, 'iw set channel' is met with an -EBUSY if doing this after the
link is up for fixed channel modes (mesh) anyway.

Comments? Any idea why this was required initially?

I don't think this patch is correct -- mac80211 will get updated even if
the device isn't even started which will likely cause trouble. Even if
not though, this all doesn't match any kind of multi-channel concept. We
treat the channel as part of the temporary setup, e.g. part of the
association. AP and mesh are the only ones that are different today I
think.

Overall, I don't think setting the channel & doing mesh setup separately
is really a good API.

From mac80211's (and other drivers if they existed) POV the channel
should be given with the mesh_join command, like for IBSS.

Now, obviously, requiring userspace to do that would be an API change.
We probably don't want that, so I would suggest to change cfg80211 to
track the channel and then pass it to join_mesh as one of the mesh
parameters. This could be made work even when somebody attempts to set
the channel before the interface is up, but we'd have to be careful
about interface type changes.

Unfortunately, when __nl80211_set_channel() is called we may or may
not have a wdev, so there is nowhere to store the interface-specific
channel and type.
We could shove these into a cfg80211_registered_device, but now just
"last channel for this wiphy" is tracked, and that doesn't seem to
help your multi-channel operation.

If the above is correct, how about we leave the existing API as-is and
simply extend join_mesh to take a channel attribute?

Also, with IBSS the desired channel is pushed to the driver along with
the setup parameters. What do you think about calling
__nl80211_set_channel() directly instead of relying on the cfg80211
driver to handle this?

We should do the same for AP mode as well, since the channel really
becomes relevant only upon start_ap(), before that there's no real
concept of a channel since you don't use it yet anyway.

Thanks,
Thomas