Multiple readers with scdaemon

NIIBE Yutaka gniibe at
Thu Sep 19 01:49:49 CEST 2019


Laurent Bigonville <bigon at> wrote:
> I'm coming back to this question after almost a year, but this is still
> an issue for me as without pcscd support, I cannot use other smartcard
> if scdaemon is running.

It is not ignored.  Sorry, it has been in low priority state.

Well, the multiple readers support with PC/SC is tracked here:

The feature is now in the master branch (this week).  I tested the
feature in my environment of Windows under qemu VM, too.  It works for
this environment of mine.

So far, it is only lightly tested.  I think that there are some
complicated use cases like: using two readers for OpenPGP cards, and
another for different card for different application.  Those cases are
not tested at all.  Your testing will be appreciated.

Still, in my opinion, I prefer access to USB device directly by libusb
(not through PC/SC service), when it is possible.

In the development of the support of multiple readers with PC/SC, I
tried to use the API of SCardGetStatusChange and SCardCancel within a
single context, so that scdaemon don't need to poll periodically.  I
realized that the API is not good enough (there are fundamental race
conditions).  So, for this time, I don't pursue to remove scdaemon's
periodical check with SCardGetStatus.  I know that this is not a perfect
situation and some users of laptop complain about possible more use of

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