npth change required for Android

[NIIBE Yutaka]

On 2013-12-09 at 22:24 -0500, Hans-Christoph Steiner wrote:
> We'd like to support using smart cards with Android, does that mean its not
> possible currently?

Well, I explain the particular issue of pinentry.  (In general, it's
not only pinentry but also any program which will be spawned and
receive signal.)

When your card reader has pinpad, it won't work, perhaps.  Pinentry
will be spawned (by gpg-agent through libassuan) to prompt user to
input PIN using pinpad.  After PIN input with pinpad, pinentry will be
killed by signal on POSIX system.

It is possible that this part (of receiving signal) won't work on
Android.  It depends on how libassuan spawns pinentry on Android.
If it doesn't inherit signal mask (of parent), it will work.
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