How to signal smart card activity at the PC/SC level? Using D-Bus? HAL?

[Bastien Nocera]

On Thu, 2009-08-27 at 14:51 +0200, Ludovic Rousseau wrote:
> Hello,
> 
> I am the maintainer of pcsc-lite [1] a middleware to access smart
> cards and smart cards readers.
> I am really new to D-Bus and HAL.
> 
> Someone asked for an applet that would indicate if a card activity is
> ongoing or not. The idea is to have the equivalent of a smart card
> reader blinking LED but in a gnome applet. The idea is nice. Some of
> my readers do not blink the LED when an APDU is exchanged so it is not
> easy to know if something is happening. In general I look at the pcscd
> debug logs but a Gnome applet would be nicer/more integrated.
> 
> My question is: what mechanism to use to convey the information?
> I was thinking of using D-Bus and also provide other information like
> reader insertion/removal, card insertion/removal. And then card
> communication status.
> 
> I need a one-way only event mechanism to signal events. Maybe D-Bus is
> too complex and HAL is the correct answer to my problem?
> 
> Is D-Bus a good enough mechanism for that? Or should I use something
> else? Is HAL more appropriate?
> Any comment on this idea?
> 
> This may be related to the smart_card_reader HAL name space proposed
> (and accepted) in [2].

It would be great if pcsc-lite could behave more like other daemons that
handle hardware:
- D-Bus interface for enumeration of devices, and device properties
- startup through udev (a-la bluetoothd), or when an application calls
one of its function (if usable even without hardware plugged in, as in
fprintd [1])

We wouldn't have to start the daemon on boot, and users that don't have
the hardware wouldn't have the burden of the daemon running in the
background.

Cheers

[1]: This is the documentation for the manager object in fprintd:
http://people.fedoraproject.org/~hadess/fprintd/docs/Manager.html