This was release with 2.5.7.

Thanks, that was the only issue building there.

Please re-open if you find other Cygwin related build problems.

You know that Cygwin is not supported but if that is the only place it should not arm to fix it.

(2) Update the documentation of default-cache-ttl zero value disabling caching.

I am going to do:
(1) Recover old behavior with max-cache-ttl = 0
(2) Update the documentation of default-cache-ttl zero value disabling caching.

I can't see any documentation that a value of 0 disables the cache. The user might have used some undefined behaviour. For example in the old code we did a housecleaning when we were idle but the new code uses a timer and another thread for flushing the cache. We could open a feature request to entire disable the cache but I bet that we will get a lot of new bug reports because users will then need to enter their passphrase too often for one operation.

It's not my intention. I didn't know the feature of disabling caching by max-cache-ttl to 0.
Well, it's a regression if a user intends so.

Lucas Mülling commented yesterday on gnupg-devel:

Here we go:

Alright, my above putenv option won't work because it modifies the session environment and thus needs to be run for each gpg-agent session (connection). Adding a putenv_startrup option would help here but this way each connection could chnage the environment - also not good. In the end a way to modify the used environment variables, as you suggested, is a better way.

Yes, the workaround is to use a pinentry wrapper script that sets the value back to the correct one and then invokes the real pinentry.

Got a simple fix for this which does two things:

1. Correctly act upon an error from the backup file writing
2. Print a warning note.

In T2169#196673, @werner wrote:

Shall we handle this with additional retry prompts, w/o a timeout? I think this makes sense because creating keys with a backup file and a passphrase is a manual task anyway.