Re: Prevent auto scan in wireless devices

[Aloisio Almeida <aloisio almeida openbossa org>]

On Wed, Jan 14, 2009 at 4:49 PM, Dan Williams <dcbw redhat com> wrote:
> On Wed, 2009-01-14 at 16:29 -0300, Aloisio Almeida wrote:
>> Well, you're right about stop background scans, it seems to change the
>> way that NM was structured to work.
>>
>> But lets suppose the use case where you have a embedded system (or a
>> notebook/netbook) and you're running on battery and you don't want use
>> wireless that time and you don't have a rf switch button. You will
>> loose power keeping your wireless card on scanning at each 20 seconds,
>> using passive scan or not.
>
> There are always mechanisms to turn off the card if you don't have a
> hardware switch; the largest hammer is to 'rmmod' the driver module.
> The second largest hammer is to power the card down with 'iwconfig wlanX
> txpower off' or something like that.  The third is to mark the
> connection as not managed by NetworkManager during the time that you
> want the wifi to be "off".

The main question is why lead to user the responsibility to save power
if (in my point of view) nm can do it automatically. The "power
saving" mode could be activated by user, by default or by an event
came from power system management and it can prevent the system to
waste power. Think as a embedded system user, you want a device that
its default behavior is always save power.

> None of these require a hardware rfkill switch.  They all accomplish
> what (I understand) you want:  no scanning when the user isn't connected
> to an AP.
>

As I said before, "no scanning" was the first idea to save power, it's
not the main goal. I want a device that has a huge battery life. Turn
on features only when asked by user is a good way. NM ( the wireless
manager) can do this turning the wireless card off after some time
disconnected and turn it on when user ask for it by user.

I prefer to loose 2 or 3 seconds to get the first list of available
APs than loose battery life during the X minutes (or hours) scanning
and keeping the wireless card on. In desktops it doesn't matter, in
notebooks it maybe doesn't affect so much, but in a embedded system i
already noticed that it matters...