On Wed, Aug 5, 2020 at 1:36 PM Ian Kent [off-list ref] wrote:

I can see in the kernel code that an error is returned if the message
buffer is full when trying to add a message, I just can't see where
to get it in the libmount code.

That's not really a communication protocol problem.

Still I need to work out how to detect it, maybe it is seen by
the code in libmount already and I simply can't see what I need
to do to recognise it ...

So I'm stuck wanting to verify I have got everything that was
sent and am having trouble moving on from that.

This is the commit that should add the overrun detection capability:

e7d553d69cf6 ("pipe: Add notification lossage handling")

Thanks,
Miklos