Thanks a lot @gniibe for this change.
I do understand and share your concerns, nevertheless are there, in my opinion valid reasons to be able to have a backup or duplicate, especially on the same or similar media type.
Consider for example giving multiple devices a chance of common interaction, using the keys for backup encryption etc. - I think there are several possible use-cases which can benefit from this.

I see the regression of gpgconf. I wonder if it's better to fix gpgconf side, too.

I see a regression with your fix. This option is even controllable with gpgconf at the basic level. It would be better to make it a dummy option.

I meant, 'card-timeout' was not intended for controlling caching PIN on card. It was for "DISCONNECT" command support.
I'm going to remove questionable documentation.
Closing.

While it's not recommended, current master has a support of sharing same raw key materials. I think that it now works (I don't try, though).
Closing.

Simply sending "KILLSCD" is implemented.

In master, I pushed a change, closing.

For future, it would make sense applying your patch, but I wonder if it works on macOS.
Let me check.

When having a backup media, I'd recommend completely different one (for example, on paper using paperkey to be stored in a locker in basement), which requires different method for recovering. Brains may be easily confused when same private key material exists in multiple similar devices.

Thanks for this @gniibe. I have long been frustrated by trying to save the correct "stubs" to have my keyring point at two different smartcards. It was common and even advocated in my former community to place one's master key on a separate smartcard (certify capability), with a different one designated for daily usage.

Thanks Gniibe San for explanation.

@blades: This feature will be available in GnuPG 2.3, which is planed to be released this year.
For Debian, Buster will come with GnuPG 2.2.12. After release of GnuPG 2.3, backport might be available (like GnuPG 2.2.x is available as backport for Stretch).

Helo and forgive me for the ignorance, Iam a new.
I subscribed to this topic because I need a fix like that, I have 2 yubikeys with same subkeys...
Now how is possible to install from master; It's about a debian based distro. Also, when this will be pushed for updates via apt-get;
Thank you.

We do not support 64 bit Windows thus this problem on Cygwin is obvious. Funny that Cygwin falls back to native Windows object in this case.

I did lot of tests in the last weeks while working on gpg-card.

Good that it works again for you.

I don't anymore think that it makes sense to fix it. Further there is no cache for PINs; that is entirely up to the card.

This was most likely a (chipcard) hardware issue. It went away after polishing the contact pads for a bit. Possibly my laptop reader applies more force...

Thanks so much your helps.
With new version 3.1.6, I can generate key on Kleopatra tool and use key stored in smartcard.

There was indeed a problem. With a test card I could reproduce the issue and fix it.

Thanks for fixing that.

That's my badness. In wait_child_thread, assuan_release may cause thread context switch to agent_reset_scd which accesses scd_local_list; This access should be serialized.
And... in start_scd, calling unlock_scd should be after unlocking start_scd_lock.

Does not happen in 2.2. Additional requirement to test this bug in master: Another connection to the scdaemon must be open. For example running scute or, easier, call "gpg --card-edit" and keep it open.

Gnuk implements the feature, and newer GnuPG shows a dialog to request pushing the ack button.