Scan in compat-wireless

Scan in compat-wireless

[Venkat Ch]

Hi All,

=A0Last week I have downloaded compat-wireless driver. I have installed
the same into my laptop which has AR242x based WiFi card. Though the
drivers are loaded correctly, the STA (my laptop) did not associate
with the nearby AP. This used to happen well with madwifi driver.

With my past experience with the details of madwifi driver, I have
browsed through the code base of compat-wireless driver. I observed
that with madwifi driver when the device is made up, the scan process
is kicked off. Where as the same is not happening in compat-wireless.
Does not the scan process need to be kicked off at the end of
ieee80211_open (net/mac80211/iface.c)?

Also for ath5k driver, both the hw_scan and sw_scan_start are not
defined. These two functions are used in ieee80211_start_scan to start
the scan process (net/mac80211/scan.c). I observed that the scan
process is not started because the above two functions are not
defined.

Is the scan functionlaity yet to be added? I have verified the TODO
list of linux-wireless page. I did not find scan in the agenda. Is
some one already implementing the functionality? Please let me know if
I need to provide further details.


Thanks & Regards
Venkat

--
Peace is its own reward
--
To unsubscribe from this list: send the line "unsubscribe linux-wireles=
s" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: Scan in compat-wireless

[Dan Williams]

On Wed, 2009-03-25 at 13:13 +0530, Venkat Ch wrote:
> Hi All,
> 
>  Last week I have downloaded compat-wireless driver. I have installed
> the same into my laptop which has AR242x based WiFi card. Though the
> drivers are loaded correctly, the STA (my laptop) did not associate
> with the nearby AP. This used to happen well with madwifi driver.
> 
> With my past experience with the details of madwifi driver, I have
> browsed through the code base of compat-wireless driver. I observed
> that with madwifi driver when the device is made up, the scan process
> is kicked off. Where as the same is not happening in compat-wireless.
> Does not the scan process need to be kicked off at the end of
> ieee80211_open (net/mac80211/iface.c)?

A scan gets kicked off when you set either SSID or BSSID using iw or
iwconfig, so that the card has some idea of what you'd like to associate
with.  Kind of pointless to scan on dev open when the card doesn't have
any idea of what you want to associate to.  Might as well defer that
until you _have_ told the card what to do.

> Also for ath5k driver, both the hw_scan and sw_scan_start are not
> defined. These two functions are used in ieee80211_start_scan to start
> the scan process (net/mac80211/scan.c). I observed that the scan
> process is not started because the above two functions are not
> defined.

I believe only Intel Wifi Link cards implement hardware scanning.  The
rest of the cards use the mac80211 software scan functionality, which
works just fine.

Dan

Re: Scan in compat-wireless

[Venkat Ch]

Hi Dan,
=A0=A0 You have a valid point. Please see my reply inline.

On Wed, Mar 25, 2009 at 9:04 PM, Dan Williams <dcbw@redhat.com> wrote:
>
> On Wed, 2009-03-25 at 13:13 +0530, Venkat Ch wrote:
> > Hi All,
> >
> > =A0Last week I have downloaded compat-wireless driver. I have insta=
lled
> > the same into my laptop which has AR242x based WiFi card. Though th=
e
> > drivers are loaded correctly, the STA (my laptop) did not associate
> > with the nearby AP. This used to happen well with madwifi driver.
> >
> > With my past experience with the details of madwifi driver, I have
> > browsed through the code base of compat-wireless driver. I observed
> > that with madwifi driver when the device is made up, the scan proce=
ss
> > is kicked off. Where as the same is not happening in compat-wireles=
s.
> > Does not the scan process need to be kicked off at the end of
> > ieee80211_open (net/mac80211/iface.c)?
>
> A scan gets kicked off when you set either SSID or BSSID using iw or
> iwconfig, so that the card has some idea of what you'd like to associ=
ate
> with. =A0Kind of pointless to scan on dev open when the card doesn't =
have
> any idea of what you want to associate to. =A0Might as well defer tha=
t
> until you _have_ told the card what to do.

I see two issues with this policy.=A0 Sorry if they are already
discussed in the mailing list. I have searched in Google and have not
seen any discussion on these.

1.=A0 It effects mobility. Every time the user moves to a new network
the SSID or BSS needs to be set manually.
2.=A0 On a similar note the upcoming standards 802.11u and 802.21 need
proactive scanning, which is not supported with the current
implementation.

I have verified this=A0 with a small test in our WLAN. It is not exactl=
y
a mobility scenario. But can be considered as a sub case of mobility
requirement.

1. Set the essid to that of the AP is using. (iwconfig wlan0 ssid
"blllllll"). The STA is associated with the AP now.
2. Switch-off AP for few minutes until the=A0 link between STA and AP i=
s
broken. (Verify this using iwconfig command)
3. Switch on the AP. The STA wont associate with the AP until you
specify, again the SSID or BSSID of the AP at the STA using iwconfig
command.

Thanks & Regards
Venkat


>
> > Also for ath5k driver, both the hw_scan and sw_scan_start are not
> > defined. These two functions are used in ieee80211_start_scan to st=
art
> > the scan process (net/mac80211/scan.c). I observed that the scan
> > process is not started because the above two functions are not
> > defined.
>
> I believe only Intel Wifi Link cards implement hardware scanning. =A0=
The
> rest of the cards use the mac80211 software scan functionality, which
> works just fine.
>
> Dan
>
>



--
Peace is its own reward
--
To unsubscribe from this list: send the line "unsubscribe linux-wireles=
s" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: Scan in compat-wireless

[Dan Williams]

On Thu, 2009-03-26 at 23:51 +0530, Venkat Ch wrote:
> Hi Dan,
>    You have a valid point. Please see my reply inline.
> 
> On Wed, Mar 25, 2009 at 9:04 PM, Dan Williams <dcbw@redhat.com> wrote:
> >
> > On Wed, 2009-03-25 at 13:13 +0530, Venkat Ch wrote:
> > > Hi All,
> > >
> > >  Last week I have downloaded compat-wireless driver. I have installed
> > > the same into my laptop which has AR242x based WiFi card. Though the
> > > drivers are loaded correctly, the STA (my laptop) did not associate
> > > with the nearby AP. This used to happen well with madwifi driver.
> > >
> > > With my past experience with the details of madwifi driver, I have
> > > browsed through the code base of compat-wireless driver. I observed
> > > that with madwifi driver when the device is made up, the scan process
> > > is kicked off. Where as the same is not happening in compat-wireless.
> > > Does not the scan process need to be kicked off at the end of
> > > ieee80211_open (net/mac80211/iface.c)?
> >
> > A scan gets kicked off when you set either SSID or BSSID using iw or
> > iwconfig, so that the card has some idea of what you'd like to associate
> > with.  Kind of pointless to scan on dev open when the card doesn't have
> > any idea of what you want to associate to.  Might as well defer that
> > until you _have_ told the card what to do.
> 
> I see two issues with this policy.  Sorry if they are already
> discussed in the mailing list. I have searched in Google and have not
> seen any discussion on these.
> 
> 1.  It effects mobility. Every time the user moves to a new network
> the SSID or BSS needs to be set manually.

Correct: if you're in an area with many access points, how is the driver
supposed to know which APs are allowed and which are not?  Certainly
connecting to any random SSID that the driver sees is a security risk,
and should not be done.

What you want is to use wpa_supplicant (or NetworkManager or something)
in userspace to control driver roaming.  Populate the wpa_supplicant
config with the list of allowed SSIDs, and then roaming works just fine.

> 2.  On a similar note the upcoming standards 802.11u and 802.21 need
> proactive scanning, which is not supported with the current
> implementation.

Again, the userspace daemon that controls roaming and/or policy
(wpa_supplicant or NetworkManager) would be triggering the proactive
scanning, then applying policy to the list of returned access points,
before choosing the "best" AP to associate with.

Dan

> I have verified this  with a small test in our WLAN. It is not exactly
> a mobility scenario. But can be considered as a sub case of mobility
> requirement.
> 
> 1. Set the essid to that of the AP is using. (iwconfig wlan0 ssid
> "blllllll"). The STA is associated with the AP now.
> 2. Switch-off AP for few minutes until the  link between STA and AP is
> broken. (Verify this using iwconfig command)
> 3. Switch on the AP. The STA wont associate with the AP until you
> specify, again the SSID or BSSID of the AP at the STA using iwconfig
> command.
> 
> Thanks & Regards
> Venkat
> 
> 
> >
> > > Also for ath5k driver, both the hw_scan and sw_scan_start are not
> > > defined. These two functions are used in ieee80211_start_scan to start
> > > the scan process (net/mac80211/scan.c). I observed that the scan
> > > process is not started because the above two functions are not
> > > defined.
> >
> > I believe only Intel Wifi Link cards implement hardware scanning.  The
> > rest of the cards use the mac80211 software scan functionality, which
> > works just fine.
> >
> > Dan
> >
> >
> 
> 
> 
> --
> Peace is its own reward
> --
> To unsubscribe from this list: send the line "unsubscribe linux-wireless" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: Scan in compat-wireless

[Johannes Berg]

[-- Attachment #1: Type: text/plain, Size: 348 bytes --]

On Thu, 2009-03-26 at 16:09 -0400, Dan Williams wrote:

> Correct: if you're in an area with many access points, how is the driver
> supposed to know which APs are allowed and which are not?  Certainly
> connecting to any random SSID that the driver sees is a security risk,
> and should not be done.

Hah. http://xkcd.com/440/

johannes

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 836 bytes --]

Scan in compat-wireless

[Venkat Ch]

Hi All,

=A0Last week I have downloaded compat-wireless driver. I have installed
the same into my laptop which has AR242x based WiFi card. Though the
drivers are loaded correctly, the STA (my laptop) did not associate
with the nearby AP. The association used to happen well when I used
madwifi driver.

With my past experience with the code details of madwifi driver, I
have browsed through the code base of compat-wireless driver. I
observed that, with madwifi driver when the device is made up, the
scan process is kicked off. Where as the same is not happening in
compat-wireless. Does not the scan process need to be kicked off at
the end of ieee80211_open (net/mac80211/iface.c)?

Also for ath5k driver, both the hw_scan and sw_scan_start are not
defined. These two functions are used in ieee80211_start_scan to start
the scan process (net/mac80211/scan.c). I observed that the scan
process is not started because the above two functions are not
defined.

Is the scan functionlaity yet to be added? I have verified the TODO
list of linux-wireless page. I did not find scan in the agenda. Is
some one already implementing the functionality? Please let me know if
I need to provide further details.


Thanks & Regards
Venkat

--
Peace is its own reward
--
To unsubscribe from this list: send the line "unsubscribe linux-wireles=
s" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html