Configuration
=============
Configuration seems to be coalescing around netlink. Among other
things, this technology provides for muliticast requests and
asynchronous event notification.
The kernel should provide generic handlers for netlink
configuraion messages, and there should be a per-device 80211_ops
(wireless_ops? akin to ethtool_ops) structure for drivers to
populate appropriately.
At init, physical devices should be represented by a "WiPHY" device,
not directly by a net_device. The list of physical devices should
be discoverable through netlink and/or sysfs. (A WiPHY device is an
abstraction representing the radio interface itself.)
Virtual wlan devices should be associated to a WiPHY device many-to-one
(one-to-one for some devices). Virtual devices correspond to a net_device.
Virtual devices will have a mode (e.g. station, AP, WDS, ad-hoc, rfmon,
raw?, other modes?) which defines its "on the air" behaviour. Should
this mode be fixed when the wlan device is created? Or something
that can be changed when the net_device is down?
It may be necessary to remove, suspend, and/or disable wlan devices
in order to add, resume, and/or enable other types of wlan devices
on the same WiPHY device (especialy true for rfmon). A mechanism is
needed for drivers to be able to influence or disallow combinations
of wlan devices in accordance with capabilities of the hardware.
Do "global" config requests go to any associated wlan device?
Or must they be directed to the WiPHY device? Does it matter?
I think we should require "global" configuration to target the WiPHY
device, while "local" configuration remains with the wlan device.
(I'm not sure how important this point is?) Either way, the WiPHY
device will need some way to be able to reject configuration requests
that are incompatible among its associated wlan devices. Since the
wlan interface implementations should not be device specific, perhaps
the 802.11 stack can be smart enough to filter-out most conflicting
config requests before they get to the WiPHY device?
--
John W. Linville
[email protected]
[since none our replies made it to the lists, here mine are again.
apologies to those who see it twice, just skip it, I only pasted my
previous replies]
> Virtual devices will have a mode (e.g. station, AP, WDS, ad-hoc, rfmon,
> raw?, other modes?) which defines its "on the air" behaviour. Should
> this mode be fixed when the wlan device is created? Or something
> that can be changed when the net_device is down?
IMHO there's not much point in allowing changes. I have a feeling that
might create icky issues you don't want to have to tackle when the
solution is easy by just not allowing it. Part of my thinking is that
different virtual types have different structures associated, so
changing it needs re-creating structures anyway. And different virtual
device types might even be provided by different kernel modules so you
don't carry around AP mode if you don't need it.
> Do "global" config requests go to any associated wlan device?
> Or must they be directed to the WiPHY device? Does it matter?
> I think we should require "global" configuration to target the WiPHY
> device, while "local" configuration remains with the wlan device.
> (I'm not sure how important this point is?)
Right [global config targets wiphy]. I do think this is an important UI
issue that userspace will have to tackle, but I think the correct way
for the kernel is to surface this issue instead of creating workarounds.
> Either way, the WiPHY
> device will need some way to be able to reject configuration requests
> that are incompatible among its associated wlan devices. Since the
> wlan interface implementations should not be device specific, perhaps
> the 802.11 stack can be smart enough to filter-out most conflicting
> config requests before they get to the WiPHY device?
I'm not sure this is worth it. While putting this into the WiPHY device
creates more logic there, putting knowledge like 'how many different
channels can this WiPHY device support' etc. into some representation
that can be used by the stack to decide is much more trouble than it is
worth.
johannes
"John W. Linville" <[email protected]> writes:
> Virtual devices will have a mode (e.g. station, AP, WDS, ad-hoc, rfmon,
> raw?, other modes?) which defines its "on the air" behaviour. Should
> this mode be fixed when the wlan device is created?
I think so. If needed one can delete and create.
> Or something
> that can be changed when the net_device is down?
IMHO: unnecessary complicates things.
> It may be necessary to remove, suspend, and/or disable wlan devices
> in order to add, resume, and/or enable other types of wlan devices
> on the same WiPHY device (especialy true for rfmon). A mechanism is
> needed for drivers to be able to influence or disallow combinations
> of wlan devices in accordance with capabilities of the hardware.
If the control messages go through the main (WiPHY) driver it can
decide and/or forward the request further, to the library.
Not sure about netlink. OTOH I'm at all not sure netlink should be
used for configuration. sysfs, ioctl seem a better options. Netlink
is better for state monitoring etc. I don't know it very well though.
> Do "global" config requests go to any associated wlan device?
Are they any global config settings?
sysctl or sysfs maybe?
> Or must they be directed to the WiPHY device? Does it matter?
If you mean "settings for a particular physical card" then WiPHY.
> I think we should require "global" configuration to target the WiPHY
> device, while "local" configuration remains with the wlan device.
If "local" means "concerning the wlan device" then sure, yes.
> (I'm not sure how important this point is?) Either way, the WiPHY
> device will need some way to be able to reject configuration requests
> that are incompatible among its associated wlan devices. Since the
> wlan interface implementations should not be device specific, perhaps
> the 802.11 stack can be smart enough to filter-out most conflicting
> config requests before they get to the WiPHY device?
I don't think so. The hardware driver should get the request first,
the rest should look like a library.
I've played with both approaches for years and I would avoid
"802.11 using the hw driver" scenario if at all possible.
--
Krzysztof Halasa
On Fri, Jan 13, 2006 at 11:32:02PM +0100, Johannes Berg wrote:
> I'm not sure this is worth it. While putting this into the WiPHY device
> creates more logic there, putting knowledge like 'how many different
> channels can this WiPHY device support' etc. into some representation
> that can be used by the stack to decide is much more trouble than it is
> worth.
Do you mean 'simultaneous' channel operation, or something more mundane
like simply 'what frequencies can I run on'?
If you're talking about the former.. things get quite complicated, but
that could be handled by having two WiPHY devices registered.
As for the latter, when you factor in the needs of 802.11d and its
dependents (802.11j, 802.11k, and others) the stack is going to need to
be aware of the available channel sets; both in the sense of hardware
support and also the various regulatory requirements.
The hardware knows what frequencies it supports. Unfortunately this has
to be a somewhat dynamic thing, as this is often not queryable until the
device firmware is up and running.
This can be accomplished by passing a static table to the
register_wiphy_device() call (or perhaps via a struct wiphy_dev
parameter) or through a more explicit, dynamic interface like:
wiphy_register_supported_frequency(hw, 2412).
- Solomon
--
Solomon Peachy ICQ: 1318344
Melbourne, FL
Quidquid latine dictum sit, altum viditur.
On Fri, 2006-01-13 at 20:17 -0500, Stuffed Crust wrote:
> If you're talking about the former.. things get quite complicated, but
> that could be handled by having two WiPHY devices registered.
The former; and yes, I thought about that too -- having a driver that
shows two physical WiPHY devices as a single logical WiPHY device and
distributes virtual devices among them...
> As for the latter, when you factor in the needs of 802.11d and its
> dependents (802.11j, 802.11k, and others) the stack is going to need to
> be aware of the available channel sets; both in the sense of hardware
> support and also the various regulatory requirements.
>
> The hardware knows what frequencies it supports. Unfortunately this has
> to be a somewhat dynamic thing, as this is often not queryable until the
> device firmware is up and running.
>
> This can be accomplished by passing a static table to the
> register_wiphy_device() call (or perhaps via a struct wiphy_dev
> parameter) or through a more explicit, dynamic interface like:
>
> wiphy_register_supported_frequency(hw, 2412).
Yeah, this is about what I thought of -- and it makes me wonder if the
stack really should be aware of the channelization, or if the WiPHY
driver might better just handle it itself.
johannes
Johannes Berg <[email protected]> writes:
> Yeah, this is about what I thought of -- and it makes me wonder if the
> stack really should be aware of the channelization, or if the WiPHY
> driver might better just handle it itself.
The latter, possibly using library functions from the stack :-)
--
Krzysztof Halasa
Stuffed Crust wrote:
> The hardware knows what frequencies it supports. Unfortunately this has
> to be a somewhat dynamic thing, as this is often not queryable until the
> device firmware is up and running.
>
> This can be accomplished by passing a static table to the
> register_wiphy_device() call (or perhaps via a struct wiphy_dev
> parameter) or through a more explicit, dynamic interface like:
>
> wiphy_register_supported_frequency(hw, 2412).
For completely programmable hardware, the stack should interact with a
module like ieee80211_geo, to help ensure the hardware stays within
legal limits.
Jeff
On Fri, 2006-01-13 at 17:19 -0500, John W. Linville wrote:
> Configuration
> =============
>
> Configuration seems to be coalescing around netlink. Among other
> things, this technology provides for muliticast requests and
> asynchronous event notification.
>
> The kernel should provide generic handlers for netlink
> configuraion messages, and there should be a per-device 80211_ops
> (wireless_ops? akin to ethtool_ops) structure for drivers to
> populate appropriately.
One other thing: capability. It's not enough to be able to configure
the device, user-space tools also have to know what the device is
capable of before they try touching it. Ie, which ciphers, protocols,
channels, etc. Similar to the IWRANGE ioctl that there is now. Half
the problem now is that you can't reliably tell what drivers support
which features, or how much they support a particular feature. Think of
ethernet devices and whether or not they support carrier detection,
there's absolutely no way to tell that now (unless they respond to
ethtool or MII, and some cards freeze if you touch them with MII too
often).
Dan
John W. Linville wrote:
> Configuration seems to be coalescing around netlink. Among other
> things, this technology provides for muliticast requests and
> asynchronous event notification.
On the other hand, the tree structure of sysfs can handle the
resource exclusivity and sharing naturaly.
A proposal of the layout:
template - template of device that can be created
profile - exclusive set of templates and other resources
plain SoftMAC card:
/sys/class/ieee80211/phy0/profile0/template0/mode # ap
| | /... # ap specific stuff
| |
| *--->/template1/mode # sta
| | /... # sta specific stuff
| |
| *--->/template2/mode # rfmon
| /... # rfmon specific stuff
|
*->/profile
/channel
/txpower
/... # other phy specific stuff
FullMAC card with mode constraints:
/sys/class/ieee80211/phy0/profile0/template0/mode # sta
| /... # sta specific stuff
|
*->/profile1/template0/mode # rfmon
| /... # rfmon specific stuff
|
*->/... # phy specific stuff
virtual interface:
/sys/class/ieee80211/sta0/parent # ->../phy0
/...
card with two chips that share some phy resources:
/sys/class/ieee80211/phy0/txpower # shared txpower
/...
/sys/class/ieee80211/phy1/parent # ->../phy0
/channel # independent
/...
/sys/class/ieee80211/phy2/parent # ->../phy0
/channel # independent
/...
Feyd
Am Freitag 13 Januar 2006 23:32 schrieb Johannes Berg:
> [Changing mode of virtual devices]
>
> IMHO there's not much point in allowing changes. I have a feeling that
> might create icky issues you don't want to have to tackle when the
> solution is easy by just not allowing it. Part of my thinking is that
> different virtual types have different structures associated, so
> changing it needs re-creating structures anyway. And different virtual
> device types might even be provided by different kernel modules so you
> don't carry around AP mode if you don't need it.
Even though it is a bit more work on kernel side, we should allow changing the
mode of virtual devices. Let's face it, even though we find multi-BSS
capabilities very interesting, 999 of 1000 users won't care due to the two
facts that IPW firmware IMHO doesn't allow it and virtual interfaces are
limited to one channel anyway. These users rightfully expect to have one
interface and be able to do all configurations on it.
Stefan
On Sat, Jan 14, 2006 at 05:07:01PM -0500, Jeff Garzik wrote:
> >This can be accomplished by passing a static table to the
> >register_wiphy_device() call (or perhaps via a struct wiphy_dev
> >parameter) or through a more explicit, dynamic interface like:
> >
> > wiphy_register_supported_frequency(hw, 2412).
>
> For completely programmable hardware, the stack should interact with a
> module like ieee80211_geo, to help ensure the hardware stays within
> legal limits.
While there is much to debate about where to draw the functionality
line, completely programmable hardware is the norm these days.
... and said code would be responsible for driving the scanning state
machines, and also for more esoteric functions like handling RADAR
traps, automatic channel switching, etc.
Handling scans is quite interesting -- I've seen hardware which requires
manual channel changing (including full RF parameter specification),
host timing for the channel dwell time, and manual probe request
issuance.. and on the other end of the spectrum, a simple "issue scan"
command that takes few, if any, parameters.
And unfortunately, many things in between.
This leads me to belive that the internal scan workflow should work
something like this:
* Userspace app issues scan request (aka "refresh AP list")
* Knowing the hardware frequency capabilities, the 802.11 stack applies
802.11d and regdomain rules to the available frequency set, and
issues multiple internal "scan request" commands to the hardware
driver. (eg "perform an initial passive sweep across the entire
2.4G band", "perform an active scan on frequencies 2412->2437
looking for ssid "HandTossed", "perform an active scan on
frequencies 5200-5400 looking for ssid "HandTossed", etc)
(note that ideally, userspace apps/libs would be at least partially
aware of 802.11d rules, but the kernel must do the RightThing if
told to "scan all available channels for any access points")
* The hardware driver takes this scan request, and maps it into the
capabilities of the hardware:
Hardware A: (very thin MAC)
- Using library code, generates an appropriate probe request frame,
translates it into a format the hardware expects/needs,
and schedules it appropriately.
- Loops through the frequency set specified, and for each:
- Issues a channel change command
- Immediately transmits the probe request (for active scans)
- Dwells for an appropriate time
- RX'ed beacon/probe response frames come down as regular 802.11
frames into the stack
- Moves to the next channel
Hardware B: (thinner MAC)
- Using library code, generates an appropriate probe request frame,
and translate it into a format the hardware expects.
- Program the probe request frame into the hardware as a probe
template.
- Loops through the frequency set specified, and for each:
- Issues a channel change command
- Wait for a scan complete signal
- RX'ed beacon/probe response frames come down as regular 802.11
frames into the stack
- Moves to the next channel
Hardware C: (thick MAC, ala prism2 or prism54)
- Issues a hardware "scan request"
- Waits for the hardware to signal "scan complete"
- Requests hardware scan results
- For each scan result, the hardware returns:
- Translate result into an 802.11 probe response frame and
pass down the regular RX path.
So as you can see, I think the channel iteration, dwell, etc should
be performed by the hardware driver itself, as the variation at the
logical "tell the hardware perform a scan" step is so extreme.
* Meanwhile, the 802.11 stack is receiving the beacons/probe responses
from the hardware via the regular rx path. It diverts these (and
other 802.11 management/control) frames, decodes them, and then adds
them to the stack's internal list of available stations, updating any
internal states/counters as necessary. (These frames could also be
echoed to a special netdev interface if desired)
(stuff like detecting an AP going away depends on us noticing a lack
of beacons arriving, for example. Most hardware does not
notify us of this event. Likewise, we should expire other
APs from our list if they go away.. etc. For AP operation we need
to maintain this STA list, period -- so why not use it across the
board? But this is another discussion for another time..)
* The 802.11 stack issues a MLME-Scan-Complete notification to
userspace.
* Interested userspace apps see this event, then query the
scan results and presents them to the user in some pretty format, or
alternatively perform automatic roaming based on scan results.
- Solomon
--
Solomon Peachy ICQ: 1318344
Melbourne, FL
Quidquid latine dictum sit, altum viditur.
Stefan Rompf wrote:
> Even though it is a bit more work on kernel side, we should allow changing
> the
> mode of virtual devices. Let's face it, even though we find multi-BSS
> capabilities very interesting, 999 of 1000 users won't care due to the two
> facts that IPW firmware IMHO doesn't allow it and virtual interfaces are
> limited to one channel anyway. These users rightfully expect to have one
> interface and be able to do all configurations on it.
Isn't that rather a question of having good user-space tools that make
deactivating one type of interface and activating another seamless?
johannes
On Sat, Jan 14, 2006 at 06:41:56PM -0500, Dan Williams wrote:
> One other thing: capability. It's not enough to be able to configure
> the device, user-space tools also have to know what the device is
> capable of before they try touching it. Ie, which ciphers, protocols,
> channels, etc. Similar to the IWRANGE ioctl that there is now. Half
> the problem now is that you can't reliably tell what drivers support
> which features, or how much they support a particular feature.
This is an absolute requirement, especially when talking about
encryption.
You'd need, for example:
CAP_WEP_64
CAP_WEP_128
CAP_WEP_256 (non-standard, but often supported)
CAP_TKIP
CAP_MICHAELMIC
CAP_AES_CCMP
Then, to make things more complicated:
CAP_KEYMAPPING (can the hardware do keymapping?)
CAP_CAN_DISABLE_HWCRYPT (so if the hardware can't do TKIP, can we
perform it on the host?)
And to make things even more complicated, I've seen hardware that
supports disabling of hardware crypto, but not toggling it on the fly,
thanks to never-fixed hardware bugs. (you have to perform a full
reset/firmware load cycle. this means you end up disabling host crypto
altogether, at least if any of the networks you want to support include
CCMP...
Other quirks -- hardware that requires host MICHAEL on transmits, but
handles it on reception, unless if the received frames are fragmented.
Other hardware that does keymapping on rx frames, but for transmits
takes the raw keydata in the tx descriptor. (but still requires host
MICHAEL)
The list goes on and on..
- Solomon
--
Solomon Peachy ICQ: 1318344
Melbourne, FL
Quidquid latine dictum sit, altum viditur.
Am Sonntag 15 Januar 2006 16:51 schrieb Johannes Berg:
> Isn't that rather a question of having good user-space tools that make
> deactivating one type of interface and activating another seamless?
Well, it's always easy to point to userspace. However, unregister_netdev()
initiates a lot of actions. IPv4 addresses and routes are removed, same for
IPv6, IPX, Appletalk etc. Stacked VLAN devices are recursively unregistered
(even though I have not tried yet if it works when I create VLANs over 802.3
emulated wlan interfaces ;-), udev bloat runs. And all this stuff has to be
restored by the nifty new configuration utility, possibly including ifindex
and future protocols.
This is from my usage pattern that I want to go into monitor mode on current
channel, look at some packets and return to the association without losing
layer 3 configuration.
So after all, it is IMHO way less painful to handle a mode change in the
kernel.
Stefan
Stefan Rompf wrote:
> Am Freitag 13 Januar 2006 23:32 schrieb Johannes Berg:
>
>> [Changing mode of virtual devices]
>>
>> IMHO there's not much point in allowing changes. I have a feeling that
>> might create icky issues you don't want to have to tackle when the
>> solution is easy by just not allowing it. Part of my thinking is that
>> different virtual types have different structures associated, so
>> changing it needs re-creating structures anyway. And different virtual
>> device types might even be provided by different kernel modules so you
>> don't carry around AP mode if you don't need it.
>
> Even though it is a bit more work on kernel side, we should allow changing the
> mode of virtual devices. Let's face it, even though we find multi-BSS
> capabilities very interesting, 999 of 1000 users won't care due to the two
> facts that IPW firmware IMHO doesn't allow it and virtual interfaces are
> limited to one channel anyway. These users rightfully expect to have one
> interface and be able to do all configurations on it.
My experience is that once you can create+destroy virtual devices you'll
never want mode changing. From a usability standpoint when you switch
modes you typically have to reconfigure lots of settings and doing
destroy old followed by create new is easier. Depending on how things
tie into hotplug you may also find things getting complicated.
Within the kernel having the operating mode of a virtual device not
change is very good. First it lets you isolate the rules for mix+match
of different virtual devices at create. Second you can partition code
so, for example, only code required to support an ap is loaded when an
ap mode virtual device exists. There are other less obvious reasons
such as firmware-based devices can load firmware based on the operating
mode at create time but if you allow mode switching then you need to
unload+load on the fly. All these things can be handled with switching
modes but the complexity is significant and the gain is minimal.
The big stumbling block I found to going with virtual devices is that it
affects user apps. I looked at doing things like auto-create a station
device for backwards compatibility but decided against it. If you
really want this behaviour it can be done by user code.
Sam
Stuffed Crust wrote:
> On Sat, Jan 14, 2006 at 05:07:01PM -0500, Jeff Garzik wrote:
>>> This can be accomplished by passing a static table to the
>>> register_wiphy_device() call (or perhaps via a struct wiphy_dev
>>> parameter) or through a more explicit, dynamic interface like:
>>>
>>> wiphy_register_supported_frequency(hw, 2412).
>> For completely programmable hardware, the stack should interact with a
>> module like ieee80211_geo, to help ensure the hardware stays within
>> legal limits.
>
> While there is much to debate about where to draw the functionality
> line, completely programmable hardware is the norm these days.
>
> ... and said code would be responsible for driving the scanning state
> machines, and also for more esoteric functions like handling RADAR
> traps, automatic channel switching, etc.
>
> Handling scans is quite interesting -- I've seen hardware which requires
> manual channel changing (including full RF parameter specification),
> host timing for the channel dwell time, and manual probe request
> issuance.. and on the other end of the spectrum, a simple "issue scan"
> command that takes few, if any, parameters.
>
> And unfortunately, many things in between.
>
> This leads me to belive that the internal scan workflow should work
> something like this:
>
> * Userspace app issues scan request (aka "refresh AP list")
>
> * Knowing the hardware frequency capabilities, the 802.11 stack applies
> 802.11d and regdomain rules to the available frequency set, and
> issues multiple internal "scan request" commands to the hardware
> driver. (eg "perform an initial passive sweep across the entire
> 2.4G band", "perform an active scan on frequencies 2412->2437
> looking for ssid "HandTossed", "perform an active scan on
> frequencies 5200-5400 looking for ssid "HandTossed", etc)
>
> (note that ideally, userspace apps/libs would be at least partially
> aware of 802.11d rules, but the kernel must do the RightThing if
> told to "scan all available channels for any access points")
>
> * The hardware driver takes this scan request, and maps it into the
> capabilities of the hardware:
>
> Hardware A: (very thin MAC)
> - Using library code, generates an appropriate probe request frame,
> translates it into a format the hardware expects/needs,
> and schedules it appropriately.
> - Loops through the frequency set specified, and for each:
> - Issues a channel change command
> - Immediately transmits the probe request (for active scans)
> - Dwells for an appropriate time
> - RX'ed beacon/probe response frames come down as regular 802.11
> frames into the stack
> - Moves to the next channel
>
> Hardware B: (thinner MAC)
> - Using library code, generates an appropriate probe request frame,
> and translate it into a format the hardware expects.
> - Program the probe request frame into the hardware as a probe
> template.
> - Loops through the frequency set specified, and for each:
> - Issues a channel change command
> - Wait for a scan complete signal
> - RX'ed beacon/probe response frames come down as regular 802.11
> frames into the stack
> - Moves to the next channel
>
> Hardware C: (thick MAC, ala prism2 or prism54)
> - Issues a hardware "scan request"
> - Waits for the hardware to signal "scan complete"
> - Requests hardware scan results
> - For each scan result, the hardware returns:
> - Translate result into an 802.11 probe response frame and
> pass down the regular RX path.
>
> So as you can see, I think the channel iteration, dwell, etc should
> be performed by the hardware driver itself, as the variation at the
> logical "tell the hardware perform a scan" step is so extreme.
>
> * Meanwhile, the 802.11 stack is receiving the beacons/probe responses
> from the hardware via the regular rx path. It diverts these (and
> other 802.11 management/control) frames, decodes them, and then adds
> them to the stack's internal list of available stations, updating any
> internal states/counters as necessary. (These frames could also be
> echoed to a special netdev interface if desired)
>
> (stuff like detecting an AP going away depends on us noticing a lack
> of beacons arriving, for example. Most hardware does not
> notify us of this event. Likewise, we should expire other
> APs from our list if they go away.. etc. For AP operation we need
> to maintain this STA list, period -- so why not use it across the
> board? But this is another discussion for another time..)
>
> * The 802.11 stack issues a MLME-Scan-Complete notification to
> userspace.
>
> * Interested userspace apps see this event, then query the
> scan results and presents them to the user in some pretty format, or
> alternatively perform automatic roaming based on scan results.
The above is a great synopsis but there is more. For example to support
roaming (and sometimes for ap operation) you want to do background
scanning; this ties in to power save mode if operating as a station.
Further you want to order your channel list to hit the most likely
channels first in case you are scanning for a specific ap--e.g. so you
can stop the foreground scan and start to associate. In terms of beacon
miss processing some parts have a hardware beacon miss interrupt based
on missed consecutive beacons but others require you to detect beacon
miss in software. Other times you need s/w bmiss detection because
you're doing something like build a repeater when the station virtual
device can't depend on the hardware to deliver a bmiss interrupt.
Then of course there's whole issue of interacting with firmware-based
cards that have limited and/or funkiness in their scanning support.
Scanning (and roaming) is really a big can 'o worms.
Sam
Stefan Rompf wrote:
> Am Sonntag 15 Januar 2006 16:51 schrieb Johannes Berg:
>
>> Isn't that rather a question of having good user-space tools that make
>> deactivating one type of interface and activating another seamless?
>
> Well, it's always easy to point to userspace. However, unregister_netdev()
> initiates a lot of actions. IPv4 addresses and routes are removed, same for
> IPv6, IPX, Appletalk etc. Stacked VLAN devices are recursively unregistered
> (even though I have not tried yet if it works when I create VLANs over 802.3
> emulated wlan interfaces ;-), udev bloat runs. And all this stuff has to be
> restored by the nifty new configuration utility, possibly including ifindex
> and future protocols.
>
> This is from my usage pattern that I want to go into monitor mode on current
> channel, look at some packets and return to the association without losing
> layer 3 configuration.
>
> So after all, it is IMHO way less painful to handle a mode change in the
> kernel.
To do what you describe I would create a monitor mode device, switch
channel, then destroy it. All the time you leave the station device
unchanged, though you probably need to disable it. This may not be
possible with all devices--i.e. for those that require different
firmware to do monitoring you will be restricted to a single virtual
device and/or operating mode.
Sam
On Sun, 2006-01-15 at 12:08 -0800, Sam Leffler wrote:
> To do what you describe I would create a monitor mode device, switch
> channel, then destroy it. All the time you leave the station device
> unchanged, though you probably need to disable it. This may not be
> possible with all devices--i.e. for those that require different
> firmware to do monitoring you will be restricted to a single virtual
> device and/or operating mode.
Yeah, I agree with this, it is much cleaner to handle in the kernel.
Think about the issues if you have a struct net_device that has 250
bytes of "payload" for the struct virtual_sta_device in it and you want
to switch that to a struct virtual_monitor_device. Icky.
johannes
On Sun, 15 Jan 2006, ext Stuffed Crust wrote:
> * Knowing the hardware frequency capabilities, the 802.11 stack applies
> 802.11d and regdomain rules to the available frequency set, and
Regarding 802.11d and regulatory domains, the stack should also be able to
stick to one regulatory domain if asked so by userspace, whatever the APs
around tell us.
Cheers,
Samuel.
On Sun, Jan 15, 2006 at 11:39:41AM -0800, Sam Leffler wrote:
> The big stumbling block I found to going with virtual devices is that it
> affects user apps. I looked at doing things like auto-create a station
> device for backwards compatibility but decided against it. If you
> really want this behaviour it can be done by user code.
Right, no reason not to just put this into a hotplug script, is there?
Is it, when it comes down to it, significantly different than automating
firmware loads for the user?
-m
--
Mike Kershaw/Dragorn <[email protected]>
GPG Fingerprint: 3546 89DF 3C9D ED80 3381 A661 D7B2 8822 738B BDB1
Experts in ancient Greek culture say that people back then didn't see their
thoughts as belonging to them. When they had a thought, it occured to them
as a god or goddess giving them an order. Apollo was telling them to be
brave. Athena was telling them to fall in love.
Now people hear a commercial for sour cream potato chips and rush out to buy.
-- Chuck Palahniuk
On Fri, 13 Jan 2006 23:32:02 +0100, Johannes Berg wrote:
> IMHO there's not much point in allowing changes. I have a feeling that
> might create icky issues you don't want to have to tackle when the
> solution is easy by just not allowing it. Part of my thinking is that
> different virtual types have different structures associated, so
> changing it needs re-creating structures anyway.
You are right. But it breaks compatibility with iwconfig unless we
emulate 'iwconfig mode' command by deleting and adding interface. This
means some events are generated, hotplug/udev gets involved etc. In the
worst case it can mean that we end up with interface with a different
name.
> And different virtual
> device types might even be provided by different kernel modules so you
> don't carry around AP mode if you don't need it.
I'm not sure about your concept of softmac modules. I wrote an e-mail
some time ago explaining why I don't think it is useful and I haven't
got any reply. Please, could you answer that e-mail first? (See
http://marc.theaimsgroup.com/?l=linux-netdev&m=113404158202233&w=2)
Could you also explain how would you implement separate module for AP
mode? How would you bind that module to the rest of ieee80211,
especially in the rx path?
Thanks,
--
Jiri Benc
SUSE Labs
On Mon, 2006-01-16 at 15:23 +0100, Jiri Benc wrote:
> You are right. But it breaks compatibility with iwconfig unless we
> emulate 'iwconfig mode' command by deleting and adding interface. This
> means some events are generated, hotplug/udev gets involved etc. In the
> worst case it can mean that we end up with interface with a different
> name.
Eh, right. In that case, I guess that dropping compatibility here would
be the only solution. Other iwconfig could still work though. I don't
know where to draw the line.
> I'm not sure about your concept of softmac modules. I wrote an e-mail
> some time ago explaining why I don't think it is useful and I haven't
> got any reply. Please, could you answer that e-mail first? (See
> http://marc.theaimsgroup.com/?l=linux-netdev&m=113404158202233&w=2)
I didn't really participate much in that thread. Maybe softmac was a bad
example for being a module -- it just seemed to fit the current model
that the in-kernel ieee80211 module follows.
> Could you also explain how would you implement separate module for AP
> mode? How would you bind that module to the rest of ieee80211,
> especially in the rx path?
Well, if you look at p80211 that davem wrote there are functions for
handling each type of the different receive frames. These could easily
be multiplexed into function pointers the module provides.
I really don't see why a plain STA mode card should be required to carry
around all the code required for AP operation -- handling associations
of clients, powersave management wrt. buffering, ... Sure, fragmentation
is needed for all, so it needs to be in the common code, and it might
make a lot of sense to unify WDS and STA modes, but AP mode requires
fundamentally different things and a lot of code that will never be
called in STA operation.
Putting it into the same modules and then probably into the same
structures just encourages bloat and interdependencies that I don't
think should be there.
johannes
On Sun, Jan 15, 2006 at 09:05:33PM +0200, Samuel Ortiz wrote:
> Regarding 802.11d and regulatory domains, the stack should also be able to
> stick to one regulatory domain if asked so by userspace, whatever the APs
> around tell us.
...and in doing so, violate the local regulatory constraints. :)
Although I believe 802.11d specifies that the 802.11d beacons should
trump whatever the user specifies. (of course, 802.11d doesn't say what
to do when there are APs out there that disagree...)
While I feel it should be *posisble* to do so, the default should be to
query the hardware for its factory default, and go with that. Allowing
the user to change the regulatory domain at will.. is a rather fuzzy
legal area, to say the least.
- Solomon
--
Solomon Peachy ICQ: 1318344
Melbourne, FL
Quidquid latine dictum sit, altum viditur.
On Sun, Jan 15, 2006 at 11:53:55AM -0800, Sam Leffler wrote:
> The above is a great synopsis but there is more. For example to support
> roaming (and sometimes for ap operation) you want to do background
> scanning; this ties in to power save mode if operating as a station.
Opportunistic roaming is one of those things that has many knobs to
twiddle, and depends a lot on the needs of the users.
But we're not actually in powersave mode -- the 802.11 stack can spit
out the NULL frames to tell the AP to buffer traffic for us. This is
trivial to do.
Scans should be specified as "non-distruptive" so the hardware driver
has to twiddle whatever bits are necessary to return the hardware to the
same state that it was in before the scan kicked in. Beyond that, the
scanning smarts are all in the 802.11 stack. The driver should be as
dumb as possible. :)
Background scanning, yes -- but there are all sorts of different
thresholds and types of 'scanning' to be done, depending on how
disruptive you are willing to be, and how capable the hardware is. Most
thin MACs don't filter out foreign BSSIDs on the same channel when
you're joined, which makes some things a lot easier.
> Further you want to order your channel list to hit the most likely
> channels first in case you are scanning for a specific ap--e.g. so you
> can stop the foreground scan and start to associate.
With my scenarios, the driver performs the sweep in the order it was
given -- if the hardware supports it, naturally.
> In terms of beacon miss processing some parts have a hardware beacon
> miss interrupt based on missed consecutive beacons but others require
> you to detect beacon miss in software. Other times you need s/w bmiss
> detection because you're doing something like build a repeater when
> the station virtual device can't depend on the hardware to deliver a
> bmiss interrupt.
Of course. The stack is going to need a set of timers regardless of the
hardware's capabilities, but having (sane) hardware beacon miss
detection capabilities makes it a bit more robust.
> Scanning (and roaming) is really a big can 'o worms.
Oh, I know. I've burned out many brain cells trying to build
supportable solutions for our customers.
- Solomon
--
Solomon Peachy ICQ: 1318344
Melbourne, FL
Quidquid latine dictum sit, altum viditur.
On Mon, Jan 16, 2006 at 03:55:55PM +0100, Johannes Berg wrote:
> I really don't see why a plain STA mode card should be required to carry
> around all the code required for AP operation -- handling associations
> of clients, powersave management wrt. buffering, ... Sure, fragmentation
From the perspective of the hardware driver, there is little AP or
STA-specific code, especially when IBSS is thrown in. Thick MACs
excepted, there's little more than "frame tx/rx, and hardware control
twiddling".
The AP/STA smarts happen in the 802.11 stack. And, speaking from
experience, it is very hard to separate them cleanly, at least not
without incurring even more overall complexity and bloat.
It's far simpler to build them intertwined, then add a bunch of #ifdefs
if you want to disable AP or STA mode individually to save space.
- Solomon
--
Solomon Peachy ICQ: 1318344
Melbourne, FL
Quidquid latine dictum sit, altum viditur.
Stuffed Crust wrote:
> On Sun, Jan 15, 2006 at 11:53:55AM -0800, Sam Leffler wrote:
>
>>The above is a great synopsis but there is more. For example to support
>>roaming (and sometimes for ap operation) you want to do background
>>scanning; this ties in to power save mode if operating as a station.
>
>
> Opportunistic roaming is one of those things that has many knobs to
> twiddle, and depends a lot on the needs of the users.
>
> But we're not actually in powersave mode -- the 802.11 stack can spit
> out the NULL frames to tell the AP to buffer traffic for us. This is
> trivial to do.
The way you implement bg scanning is to notify the ap you are going into
power save mode before you leave the channel (in sta mode). Hence bg
scanning and power save operation interact.
>
> Scans should be specified as "non-distruptive" so the hardware driver
> has to twiddle whatever bits are necessary to return the hardware to the
> same state that it was in before the scan kicked in. Beyond that, the
> scanning smarts are all in the 802.11 stack. The driver should be as
> dumb as possible. :)
See above. Doing bg scanning well is a balancing act and restoring
hardware state is the least of your worries (hopefully); e.g. what's the
right thing to do when you get a frame to transmit while off-channel
scanning, how often should you return to the bss channel?
>
> Background scanning, yes -- but there are all sorts of different
> thresholds and types of 'scanning' to be done, depending on how
> disruptive you are willing to be, and how capable the hardware is. Most
> thin MACs don't filter out foreign BSSIDs on the same channel when
> you're joined, which makes some things a lot easier.
Er, you need to listen to at least beacons from other ap's if you're in
11g so you can detect overlapping bss and enable protection. There are
other ways to handle this but that's one.
>
>
>>Further you want to order your channel list to hit the most likely
>>channels first in case you are scanning for a specific ap--e.g. so you
>>can stop the foreground scan and start to associate.
>
>
> With my scenarios, the driver performs the sweep in the order it was
> given -- if the hardware supports it, naturally.
Channel ordering is useful no matter who specifies it. If you offload
the ordering to the upper layers then they need to be aware of the
regdomain constraints. Probably not a big deal but then you need to
synchronize info between layers or export it. And there's other
regdomain-related info that may want to be considered such as max
txpower. I'm just saying if you want to do a good job there's lots of
work here.
>
>
>>In terms of beacon miss processing some parts have a hardware beacon
>>miss interrupt based on missed consecutive beacons but others require
>>you to detect beacon miss in software. Other times you need s/w bmiss
>>detection because you're doing something like build a repeater when
>>the station virtual device can't depend on the hardware to deliver a
>>bmiss interrupt.
>
>
> Of course. The stack is going to need a set of timers regardless of the
> hardware's capabilities, but having (sane) hardware beacon miss
> detection capabilities makes it a bit more robust.
>
>
>>Scanning (and roaming) is really a big can 'o worms.
>
>
> Oh, I know. I've burned out many brain cells trying to build
> supportable solutions for our customers.
I don't recall seeing well-developed scanning code in either of the
proposed stacks.
Sam
Stuffed Crust wrote:
> On Mon, Jan 16, 2006 at 03:55:55PM +0100, Johannes Berg wrote:
>
>>I really don't see why a plain STA mode card should be required to carry
>>around all the code required for AP operation -- handling associations
>>of clients, powersave management wrt. buffering, ... Sure, fragmentation
>
>
> From the perspective of the hardware driver, there is little AP or
> STA-specific code, especially when IBSS is thrown in. Thick MACs
> excepted, there's little more than "frame tx/rx, and hardware control
> twiddling".
>
> The AP/STA smarts happen in the 802.11 stack. And, speaking from
> experience, it is very hard to separate them cleanly, at least not
> without incurring even more overall complexity and bloat.
>
> It's far simpler to build them intertwined, then add a bunch of #ifdefs
> if you want to disable AP or STA mode individually to save space.
Perhaps you haven't hit some of the more recent standards that place
more of a burden on the ap implementation? Also some vendor-specific
protocol features suck up space for ap mode only and it is nice to be
able to include them only as needed.
There are several advantages to splitting up the code such as reduced
audit complexity and real space savings but I agree that it is an open
question whethere there's a big gain to modularizing the code by
operating mode.
Sam
On Mon, 2006-01-16 at 12:28 -0500, Stuffed Crust wrote:
> Scans should be specified as "non-distruptive" so the hardware driver
> has to twiddle whatever bits are necessary to return the hardware to the
> same state that it was in before the scan kicked in. Beyond that, the
> scanning smarts are all in the 802.11 stack. The driver should be as
> dumb as possible. :)
This is quite important... from a user perspective, it might be 2, 5, or
15 seconds before the card can actually scan all channels.
Unfortunately, background (passive) scanning by definition can't find
all access points, so you're going to need to do active scanning.
However, that active scanning should be controlled by userspace, not the
driver. Only userspace knows what policies the user him/herself has set
on powersaving mode.
> Background scanning, yes -- but there are all sorts of different
> thresholds and types of 'scanning' to be done, depending on how
> disruptive you are willing to be, and how capable the hardware is. Most
> thin MACs don't filter out foreign BSSIDs on the same channel when
> you're joined, which makes some things a lot easier.
Scanning has the tradeoff of updated network list vs. saving power +
network disruption. The user, or programs delegated by the user, need
to make that choice, not the stack or the driver.
-------------
Furthermore, and this is also extremely important, user apps need to
know when the scan is done. From my look at drivers, _all_ cards know
when the hardware is in scanning states, and when its done. What many
don't do is communicate that information to userspace via wireless
events. The userspace app that requested scanning is then stuck
busy-waiting for the SIOCGIWSCAN to return success, which just sucks.
Much better if all drivers had the wireless event so that the userspace
app could just fire off the scan with SIOCSIWSCAN, and parse the results
when the event comes back rather than spinning.
In the netlink world, this would of course be done by multicasting the
"Scan Done" message to all interested clients, which would be just as
good.
Dan
On Mon, 16 Jan 2006, ext Stuffed Crust wrote:
> On Sun, Jan 15, 2006 at 09:05:33PM +0200, Samuel Ortiz wrote:
> > Regarding 802.11d and regulatory domains, the stack should also be able to
> > stick to one regulatory domain if asked so by userspace, whatever the APs
> > around tell us.
>
> ...and in doing so, violate the local regulatory constraints. :)
The other option is to conform to whatever the AP you associate with
advertises. In fact, this is how it should be done according to 802.11d.
Unfortunately, this doesn't ensure local regulatory constraints compliance
unless you expect each and every APs to do the Right Thing ;-)
> Allowing
> the user to change the regulatory domain at will.. is a rather fuzzy
> legal area, to say the least.
IMHO, strictly sticking to 802.11d is also somehow legally fuzzy as you're
as legal as the network you're joining.
Cheers,
Samuel.
On Mon, Jan 16, 2006 at 08:51:31PM +0200, Samuel Ortiz wrote:
> On Mon, 16 Jan 2006, ext Stuffed Crust wrote:
>
> > On Sun, Jan 15, 2006 at 09:05:33PM +0200, Samuel Ortiz wrote:
> > > Regarding 802.11d and regulatory domains, the stack should also be able to
> > > stick to one regulatory domain if asked so by userspace, whatever the APs
> > > around tell us.
> >
> > ...and in doing so, violate the local regulatory constraints. :)
> The other option is to conform to whatever the AP you associate with
> advertises. In fact, this is how it should be done according to 802.11d.
> Unfortunately, this doesn't ensure local regulatory constraints compliance
> unless you expect each and every APs to do the Right Thing ;-)
If regulators come down on someone, it seems like common sense
that they would be more lenient on mobile stations complying with a
misconfigured AP than they would be with a mobile station ignoring a
properly configured AP? I know expecting common sense from government
regulators is optimistic, but still... :-)
Of course when we are the AP, the ability to adjust these parameters
could be very important. No?
John
--
John W. Linville
[email protected]
On Mon, 16 Jan 2006, ext Stuffed Crust wrote:
> Background scanning, yes -- but there are all sorts of different
> thresholds and types of 'scanning' to be done, depending on how
> disruptive you are willing to be, and how capable the hardware is. Most
> thin MACs don't filter out foreign BSSIDs on the same channel when
> you're joined, which makes some things a lot easier.
That is true, thin MACs usually don't filter beacons on the same channel.
But in some cases (mainly power saving), you really want to avoid
receiving useless beacons and having the host woken up for each of them.
You may even want to not receive all the useful ones (the ones coming from
the AP you're joined with) if your softmac allows that.
This kind of beacon filtering is a big power saver, which is one of the
most important requirement for some platforms (phones, PDA, etc...).
Cheers,
Samuel.
On Mon, Jan 16, 2006 at 09:54:15AM -0800, Sam Leffler wrote:
> The way you implement bg scanning is to notify the ap you are going into
> power save mode before you leave the channel (in sta mode). Hence bg
> scanning and power save operation interact.
That is not "powersave operation" -- that is telling the AP we are going
into powersave, but not actually going into powersave -- Actual
powersave operation would need to be disabled if we go into a scan, as
we need to have the rx path powered up and ready to hear anything out
there for the full channel dwell time.
> See above. Doing bg scanning well is a balancing act and restoring
> hardware state is the least of your worries (hopefully); e.g. what's the
> right thing to do when you get a frame to transmit while off-channel
> scanning, how often should you return to the bss channel?
Disallow all other transmits (either by failing them altogether, or by
buffering them up, which I think is better) while performing the scan.
If we are (continually) scanning because we don't have an association,
then we shouldn't be allowing any traffic through the stack anyway.
At the end of each scan pass, you return to the original channel, then
return "scan complete" to the stack/userspace. at this point any
pending transmits can go out, and if another scan pass is desired, it
will happen then.
> Er, you need to listen to at least beacons from other ap's if you're in
> 11g so you can detect overlapping bss and enable protection. There are
> other ways to handle this but that's one.
If you can't hear the traffic, then it doesn't count for purposes of ER
protection -- but that said, this only matters for AP operation, so APs
shouldn't filter out anyone else's becacons. STAs should respect the
"use ER Protection" bit in the AP's beacon, so can filter out traffic
that doesn't match the configured BSSID.
> >Oh, I know. I've burned out many brain cells trying to build
> >supportable solutions for our customers.
>
> I don't recall seeing well-developed scanning code in either of the
> proposed stacks.
I've only looked into the pre-2.6-merged HostAP stack, so I can't
comment on what's publically available. I'll have a look at the GPL'ed
DeviceScape stack when I have more time.
Most of what I've going on about is derived from my experience from
commercial 802.11 work I've done over the past few years.
- Solomon
--
Solomon Peachy ICQ: 1318344
Melbourne, FL
Quidquid latine dictum sit, altum viditur.
On Mon, Jan 16, 2006 at 09:07:52PM +0200, Samuel Ortiz wrote:
> That is true, thin MACs usually don't filter beacons on the same channel.
> But in some cases (mainly power saving), you really want to avoid
> receiving useless beacons and having the host woken up for each of them.
> You may even want to not receive all the useful ones (the ones coming from
> the AP you're joined with) if your softmac allows that.
BSSID filtering doesn't matter as far as 802.11 powersave is concerned
-- the power savings come from disabling the RF/BBP components. In
other words, you can't receive or transmit traffic.
If you're respecting the AP's beacon interval/DTIM settings, you only
wake up every couple of beacon intervals and listen for a beacon. IF
there's traffic waiting for you, then you wake up your transmitter, send
out a PSPOLL (or NULL/PSEnd) frame, get your traffic, then go back to
sleep again.
You may hear another beacon when the STA is awake, you may not. BSSID
filtering has nothing to do with 802.11 power save, but rather is
intented to reduce the host load (interrupts, processing overhead) and
thus the host power consumption.
> This kind of beacon filtering is a big power saver, which is one of the
> most important requirement for some platforms (phones, PDA, etc...).
You need to be clear if you're talking about 802.11 powersave, versus
"power savings stemming from reducing the load on the host system",
which is where BSSID filtering is beneficial.
- Solomon
--
Solomon Peachy ICQ: 1318344
Melbourne, FL
Quidquid latine dictum sit, altum viditur.
On Mon, 16 Jan 2006, ext Stuffed Crust wrote:
> You may hear another beacon when the STA is awake, you may not. BSSID
> filtering has nothing to do with 802.11 power save, but rather is
> intented to reduce the host load (interrupts, processing overhead) and
> thus the host power consumption.
I know that and I know a bit about 802.11 PS as well.
I was talking about host powersaving, not 802.11. Sorry for the confusion.
What I meant is that having an 802.11 stack capable of living with less
than a beacon every couple of beacon intervals would be nice as well.
Cheers,
Samuel.
Stuffed Crust wrote:
> On Mon, Jan 16, 2006 at 09:54:15AM -0800, Sam Leffler wrote:
>> The way you implement bg scanning is to notify the ap you are going into
>> power save mode before you leave the channel (in sta mode). Hence bg
>> scanning and power save operation interact.
>
> That is not "powersave operation" -- that is telling the AP we are going
> into powersave, but not actually going into powersave -- Actual
> powersave operation would need to be disabled if we go into a scan, as
> we need to have the rx path powered up and ready to hear anything out
> there for the full channel dwell time.
Please read what I wrote again. Station mode power save work involves
communicating with the ap and managing the hardware. The first
interacts with bg scanning. We haven't even talked about how to handle
sta mode power save.
>
>> See above. Doing bg scanning well is a balancing act and restoring
>> hardware state is the least of your worries (hopefully); e.g. what's the
>> right thing to do when you get a frame to transmit while off-channel
>> scanning, how often should you return to the bss channel?
>
> Disallow all other transmits (either by failing them altogether, or by
> buffering them up, which I think is better) while performing the scan.
Not necessarily in my experience.
>
> If we are (continually) scanning because we don't have an association,
> then we shouldn't be allowing any traffic through the stack anyway.
If you do not have an association you are not doing bg scanning.
>
> At the end of each scan pass, you return to the original channel, then
> return "scan complete" to the stack/userspace. at this point any
> pending transmits can go out, and if another scan pass is desired, it
> will happen then.
If you wait until the end of the scan to return to the bss channel then
you potentially miss buffered mcast frames. You can up the station's
listen interval but that only gets you so far. As I said there are
tradeoffs in doing this.
>
>> Er, you need to listen to at least beacons from other ap's if you're in
>> 11g so you can detect overlapping bss and enable protection. There are
>> other ways to handle this but that's one.
>
> If you can't hear the traffic, then it doesn't count for purposes of ER
> protection -- but that said, this only matters for AP operation, so APs
> shouldn't filter out anyone else's becacons. STAs should respect the
> "use ER Protection" bit in the AP's beacon, so can filter out traffic
> that doesn't match the configured BSSID.
Sorry I meant this was needed for ap operation.
>
>>> Oh, I know. I've burned out many brain cells trying to build
>>> supportable solutions for our customers.
>> I don't recall seeing well-developed scanning code in either of the
>> proposed stacks.
>
> I've only looked into the pre-2.6-merged HostAP stack, so I can't
> comment on what's publically available. I'll have a look at the GPL'ed
> DeviceScape stack when I have more time.
>
> Most of what I've going on about is derived from my experience from
> commercial 802.11 work I've done over the past few years.
Ditto.
Sam
On Mon, Jan 16, 2006 at 10:00:18AM -0800, Sam Leffler wrote:
> Perhaps you haven't hit some of the more recent standards that place
> more of a burden on the ap implementation? Also some vendor-specific
> protocol features suck up space for ap mode only and it is nice to be
> able to include them only as needed.
While there is more work to be done on the AP side, and that code may
even be easily wrapped in an #ifdef, the majority of the complexity is
shared by both the station and the AP. It's worth mentioning that the
802.11 specs do not generally differentiate between "APs vs non-APs" --
they're all "STAs" of equal capabilities.
This is at least true of 802.11d, 802.11e, 802.11i
(supplicant/authenticator notwithstanding), 802.11j, and 802.11k. The
general difference is that the AP needs to be aware of the state of its
associated STAs, and perform different actions depending on configured
policy and the STAs' states, whereas the STAs generally do what the AP
tells them to do.
> There are several advantages to splitting up the code such as reduced
> audit complexity and real space savings but I agree that it is an open
> question whethere there's a big gain to modularizing the code by
> operating mode.
I agree that there would be some space savings, but they'd be relatively
small, at least if the stack is designed to be generic. This would make
the most difference for tiny/embedded systems -- but they'd want to use
#ifdefs to disable all AP code entirely, which includes all of the "if
(ap_mode) { } else { }" clauses that would litter the whole codebase,
regardless of modularity. (then if we use function pointers... that's a
*lot* of virtual functions..)
- Solomon
--
Solomon Peachy ICQ: 1318344
Melbourne, FL
Quidquid latine dictum sit, altum viditur.
On Mon, 16 Jan 2006, ext John W. Linville wrote:
> On Mon, Jan 16, 2006 at 08:51:31PM +0200, Samuel Ortiz wrote:
> > On Mon, 16 Jan 2006, ext Stuffed Crust wrote:
> >
> > > On Sun, Jan 15, 2006 at 09:05:33PM +0200, Samuel Ortiz wrote:
> > > > Regarding 802.11d and regulatory domains, the stack should also be able to
> > > > stick to one regulatory domain if asked so by userspace, whatever the APs
> > > > around tell us.
> > >
> > > ...and in doing so, violate the local regulatory constraints. :)
> > The other option is to conform to whatever the AP you associate with
> > advertises. In fact, this is how it should be done according to 802.11d.
> > Unfortunately, this doesn't ensure local regulatory constraints compliance
> > unless you expect each and every APs to do the Right Thing ;-)
>
> If regulators come down on someone, it seems like common sense
> that they would be more lenient on mobile stations complying with a
> misconfigured AP than they would be with a mobile station ignoring a
> properly configured AP? I know expecting common sense from government
> regulators is optimistic, but still... :-)
Well, I'd rather trust a governement regulated network than my neighbour's
AP ;-) In fact, some phones set their 802.11 regulatory domain based on
the information they received from a somehow government regulated network,
e.g. a GSM one.
Cheers,
Samuel.
On Mon, Jan 16, 2006 at 12:14:08PM -0800, Sam Leffler wrote:
> Please read what I wrote again. Station mode power save work involves
> communicating with the ap and managing the hardware. The first
> interacts with bg scanning. We haven't even talked about how to handle
> sta mode power save.
I think we're arguing over semantics; what's important here is that the
STA tells the AP to buffer frames while we're performing a scan,
correct?
> If you wait until the end of the scan to return to the bss channel then
> you potentially miss buffered mcast frames. You can up the station's
> listen interval but that only gets you so far. As I said there are
> tradeoffs in doing this.
An excellent point. This is particularly relevant for APs that have a
DTIM interval of 1 -- if you're doing a passive scan, the dwell time on
that other channel (you need at least one beacon interval) could cause
you to miss bufferend MCAST frames.
In all fairness I don't think I've seen any implementations that handle
this cleanly.
- Solomon
--
Solomon Peachy ICQ: 1318344
Melbourne, FL
Quidquid latine dictum sit, altum viditur.
On Mon, Jan 16, 2006 at 10:16:06PM +0200, Samuel Ortiz wrote:
> Well, I'd rather trust a governement regulated network than my neighbour's
> AP ;-) In fact, some phones set their 802.11 regulatory domain based on
> the information they received from a somehow government regulated network,
> e.g. a GSM one.
The asumption is that 802.11d information, like current "regdomain"
settings, is fixed and not user-configurable. If the regdomain is
changeable by the user, that unit would not be approved for sale in that
particular locale.
(Now 802.11d doesn't specify what to do when you hear two conflicting
802.11d beacons.... there go those assumptions again..)
Stations respecting 802.11d rules are not allowed to transmit on any
supported frequency until they hear an AP on that frequency first.
This essentially means that all scans are passive until we hear an AP,
and we can't transmit on any other (presumably still silent) frequencies
unless we hear an 802.11d beacon that says we can.
- Solomon
--
Solomon Peachy ICQ: 1318344
Melbourne, FL
Quidquid latine dictum sit, altum viditur.
On Llu, 2006-01-16 at 14:06 -0500, John W. Linville wrote:
> If regulators come down on someone, it seems like common sense
> that they would be more lenient on mobile stations complying with a
> misconfigured AP than they would be with a mobile station ignoring a
> properly configured AP? I know expecting common sense from government
> regulators is optimistic, but still... :-)
I can't guess on the subject of US regulators but for the UK experience
in other communities (eg amateur radio), and public statements indicate
that their high priorities are interference with emergency services and
the like.
Concerns of direct relevance are
- transmitting on unlicensed frequencies (and 802.11 channel allocations
are dependant on nation - even within the EU)
- power violation
- anything else causing interference to other legitimate users at a
radio level
I would expect equipment to honour the subset of configurations that
meet BOTH the regulatory domain the system believes it exists within
(which may change dynamically!) AND the AP advertisement.
If I have told my equipment to obey UK law I expect it to do so. If I
hop on the train to France and forget to revise my configuration I'd
prefer it also believed the APs
Alan
On Mon, Jan 16, 2006 at 10:24:41PM +0000, Alan Cox wrote:
> I would expect equipment to honour the subset of configurations that
> meet BOTH the regulatory domain the system believes it exists within
> (which may change dynamically!) AND the AP advertisement.
>
> If I have told my equipment to obey UK law I expect it to do so. If I
> hop on the train to France and forget to revise my configuration I'd
> prefer it also believed the APs
Yes, this is an excellent point. I suppose this could result in
a non-functional configuration, but that is probably better than
conflicting w/ the local authorities... :-)
John
--
John W. Linville
[email protected]
On Mon, Jan 16, 2006 at 10:24:41PM +0000, Alan Cox wrote:
> If I have told my equipment to obey UK law I expect it to do so. If I
> hop on the train to France and forget to revise my configuration I'd
> prefer it also believed the APs
It's not that you might forget to revise your configuration, but that
the vast majority of users will not revise anything, and still expect
things to "just work". Kind of like multi-band cell phones.
This isn't that big of a deal in the 2.4GHz band, but when you start
talking about 5GHz, especially in France, things get a lot trickier.
Of course, all of this automagic "just work" crap only affects the STAs.
For AP operation, we have to trust the user to set the correct locale --
I don't see any way of including a sane "just-works" default in the
stock kernel.org tree, so I think the default should be be "none". This
way the user is forced to explicitly set the regdomain in order for the
AP startup to succeed.
...and pray that the AP isn't migrating to a different regdomain, but
there's really nothing anyone can do about that.
- Solomon
--
Solomon Peachy ICQ: 1318344
Melbourne, FL
Quidquid latine dictum sit, altum viditur.
On Jan 17, 2006, at 13:41, Stuffed Crust wrote:
> On Mon, Jan 16, 2006 at 10:24:41PM +0000, Alan Cox wrote:
>> If I have told my equipment to obey UK law I expect it to do so.
>> If I hop on the train to France and forget to revise my
>> configuration I'd prefer it also believed the APs
>
> It's not that you might forget to revise your configuration, but
> that the vast majority of users will not revise anything, and still
> expect things to "just work". Kind of like multi-band cell phones.
Alan's point is still very valid. From a poweruser point of view, if
I specifically tell my wireless client "You must obey US laws", and
then I wander over past a broken imported AP, I don't want my client
to _expand_ its allowable range. IMHO, userspace should be able to
forcibly restrict wireless frequencies to a certain regdomain (or
leave unrestricted and passive-scan-only), and specify how AP/
configured regdomains act. Given the range of possibilities, I think
that a userspace daemon monitoring events and dynamically configuring
the useable frequencies would best. That way the userspace daemon
could be configured to ignore APs, union/intersect the APs with the
configured regdomain, ignore the configured regdomain in the presence
of APs, etc.
Cheers,
Kyle Moffett
--
I lost interest in "blade servers" when I found they didn't throw
knives at people who weren't supposed to be in your machine room.
-- Anthony de Boer
Am Sonntag 15 Januar 2006 21:11 schrieb Johannes Berg:
> [iwconfig mode ...]
>
> Yeah, I agree with this, it is much cleaner to handle in the kernel.
> Think about the issues if you have a struct net_device that has 250
> bytes of "payload" for the struct virtual_sta_device in it and you want
> to switch that to a struct virtual_monitor_device. Icky.
Well, nobody forces you to allocate dev->priv together with the net_device,
you can set and change this pointer yourself. So I don't see a problem here.
Stefan