[PATCH 3/4 V2] mac80211: add last beacon time in scan list

[PATCH 3/4 V2] mac80211: add last beacon time in scan list

[Tomas Winkler]

From: Emmanuel Grumbach <emmanuel.grumbach@intel.com>

This patch adds the interval between the scan results and the last time a
beacon was received in the result of the scan.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
---
 net/mac80211/mlme.c |   14 ++++++++++++++
 1 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/net/mac80211/mlme.c b/net/mac80211/mlme.c
index 7b930d1..e76e62a 100644
--- a/net/mac80211/mlme.c
+++ b/net/mac80211/mlme.c
@@ -4658,12 +4658,26 @@ ieee80211_sta_scan_result(struct net_device *dev,
 		char *buf;
 		buf = kmalloc(30, GFP_ATOMIC);
 		if (buf) {
+			unsigned long mid_range = (-1) / 2 + 1;
+			unsigned long time_diff;
+
 			memset(&iwe, 0, sizeof(iwe));
 			iwe.cmd = IWEVCUSTOM;
 			sprintf(buf, "tsf=%016llx", (unsigned long long)(bss->timestamp));
 			iwe.u.data.length = strlen(buf);
 			current_ev = iwe_stream_add_point(current_ev, end_buf,
 							  &iwe, buf);
+			memset(&iwe, 0, sizeof(iwe));
+
+			iwe.cmd = IWEVCUSTOM;
+			time_diff = jiffies - bss->last_update > mid_range ?
+				jiffies - bss->last_update :
+				bss->last_update - jiffies;
+			sprintf(buf, "Last beacon:%dms ago",
+				jiffies_to_msecs(time_diff));
+			iwe.u.data.length = strlen(buf);
+			current_ev = iwe_stream_add_point(current_ev, end_buf,
+							  &iwe, buf);
 			kfree(buf);
 		}
 	}
-- 
1.5.4.1

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Re: [PATCH 3/4 V2] mac80211: add last beacon time in scan list

[Pavel Roskin]

On Wed, 2008-06-25 at 15:17 +0300, Tomas Winkler wrote:
> From: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
> 
> This patch adds the interval between the scan results and the last time a
> beacon was received in the result of the scan.
> 
> Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
> Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
> ---
>  net/mac80211/mlme.c |   14 ++++++++++++++
>  1 files changed, 14 insertions(+), 0 deletions(-)
> 
> diff --git a/net/mac80211/mlme.c b/net/mac80211/mlme.c
> index 7b930d1..e76e62a 100644
> --- a/net/mac80211/mlme.c
> +++ b/net/mac80211/mlme.c
> @@ -4658,12 +4658,26 @@ ieee80211_sta_scan_result(struct net_device *dev,
>  		char *buf;
>  		buf = kmalloc(30, GFP_ATOMIC);
>  		if (buf) {
> +			unsigned long mid_range = (-1) / 2 + 1;

What is that?  I guess that's where Riemann's zeta function has its
non-trivial roots :-)

> +			time_diff = jiffies - bss->last_update > mid_range ?
> +				jiffies - bss->last_update :
> +				bss->last_update - jiffies;

That's pretty hairy.  Do we really lack a function to calculate time
difference?

> +			sprintf(buf, "Last beacon:%dms ago",
> +				jiffies_to_msecs(time_diff));

You lost space after the colon for some reason.

-- 
Regards,
Pavel Roskin

Re: [PATCH 3/4 V2] mac80211: add last beacon time in scan list

[drago01]

On Wed, Jun 25, 2008 at 5:58 PM, Pavel Roskin <proski@gnu.org> wrote:
>
>> +                     time_diff = jiffies - bss->last_update > mid_range ?
>> +                             jiffies - bss->last_update :
>> +                             bss->last_update - jiffies;
>
> That's pretty hairy.  Do we really lack a function to calculate time
> difference?

what about elapsed_jiffies() in iwl-helpers.h ?...
should be moved to a generic place (include/linux/jiffies.h) so that
other users can access it.

Re: [PATCH 3/4 V2] mac80211: add last beacon time in scan list

[Johannes Berg]

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On Wed, 2008-06-25 at 11:58 -0400, Pavel Roskin wrote:

> > +			unsigned long mid_range = (-1) / 2 + 1;
> 
> What is that?  I guess that's where Riemann's zeta function has its
> non-trivial roots :-)

The Pavel hypothesis: "The Riemann hypothesis is correct when calculated
in 32-bit integers" is obviously wrong ;)

> > +			time_diff = jiffies - bss->last_update > mid_range ?
> > +				jiffies - bss->last_update :
> > +				bss->last_update - jiffies;
> 
> That's pretty hairy.  Do we really lack a function to calculate time
> difference?

Actually, come to think of it, isn't just doing the difference as in teh
original patch correct in 32-bit unsigned integers? It'll wrap around a
bit but that's ok, no?

johannes

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Re: [PATCH 3/4 V2] mac80211: add last beacon time in scan list

[Tomas Winkler]

On Wed, Jun 25, 2008 at 7:12 PM, Johannes Berg
<johannes@sipsolutions.net> wrote:
> On Wed, 2008-06-25 at 11:58 -0400, Pavel Roskin wrote:
>
>> > +                   unsigned long mid_range = (-1) / 2 + 1;
>>
>> What is that?  I guess that's where Riemann's zeta function has its
>> non-trivial roots :-)

>
> The Pavel hypothesis: "The Riemann hypothesis is correct when calculated
> in 32-bit integers" is obviously wrong ;)
>
Welcome to the Desert of the Real

>> > +                   time_diff = jiffies - bss->last_update > mid_range ?
>> > +                           jiffies - bss->last_update :
>> > +                           bss->last_update - jiffies;
>>
>> That's pretty hairy.  Do we really lack a function to calculate time
>> difference?

This is simplest as you can get under assumption that times are not
apart more then 1/2 of UL.
 It would be overkill to translate it to timeval or anything we have
diff function for.

> Actually, come to think of it, isn't just doing the difference as in teh
> original patch correct in 32-bit unsigned integers? It'll wrap around a
> bit but that's ok, no?

It would make a very recent beacon to be like half an hour old on
wraps, wouldn't it?
But I'm good also with the old version as well. Just ACK one

Tomas

Re: [PATCH 3/4 V2] mac80211: add last beacon time in scan list

[Pavel Roskin]

On Thu, 2008-06-26 at 01:26 +0300, Tomas Winkler wrote:
> On Wed, Jun 25, 2008 at 7:12 PM, Johannes Berg
> <johannes@sipsolutions.net> wrote:
> > On Wed, 2008-06-25 at 11:58 -0400, Pavel Roskin wrote:
> >
> >> > +                   unsigned long mid_range = (-1) / 2 + 1;
> >>
> >> What is that?  I guess that's where Riemann's zeta function has its
> >> non-trivial roots :-)
> 
> >
> > The Pavel hypothesis: "The Riemann hypothesis is correct when calculated
> > in 32-bit integers" is obviously wrong ;)
> >
> Welcome to the Desert of the Real

Welcome to C.  mid_range is 1, as you can easily check.

> >> > +                   time_diff = jiffies - bss->last_update > mid_range ?
> >> > +                           jiffies - bss->last_update :
> >> > +                           bss->last_update - jiffies;
> >>
> >> That's pretty hairy.  Do we really lack a function to calculate time
> >> difference?
> 
> This is simplest as you can get under assumption that times are not
> apart more then 1/2 of UL.
>  It would be overkill to translate it to timeval or anything we have
> diff function for.

Why would jiffies ever lag behind bss->last_update?  When would
(bss->last_update - jiffies) make sense?  If it makes sense, how about
indicating it somehow?  It would be a value that decreases over time.  

> > Actually, come to think of it, isn't just doing the difference as in teh
> > original patch correct in 32-bit unsigned integers? It'll wrap around a
> > bit but that's ok, no?
> 
> It would make a very recent beacon to be like half an hour old on
> wraps, wouldn't it?

No.  Why would it?  Can you give an example?  If you are not increasing
precision, wraparounds should make no difference.

-- 
Regards,
Pavel Roskin

Re: [PATCH 3/4 V2] mac80211: add last beacon time in scan list

[Johannes Berg]

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> > > Actually, come to think of it, isn't just doing the difference as in teh
> > > original patch correct in 32-bit unsigned integers? It'll wrap around a
> > > bit but that's ok, no?
> > 
> > It would make a very recent beacon to be like half an hour old on
> > wraps, wouldn't it?
> 
> No.  Why would it?  Can you give an example?  If you are not increasing
> precision, wraparounds should make no difference.

That was my mistake, somehow I thought we'd have to account for wraps,
but that was wrong I think.

Let's use v1.

johannes

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