Subject: Re: [PATCH bpf-next 2/3] libbpf: Support configurable pinning of maps from BTF annotations

From: Toke Høiland-Jørgensen <[email-masked]>
Date: Wed, 23 Oct 2019 15:05:18 +0200

> You are worried about the case where an application should be able to
> unpin the map before loading a new one so it doesn't get reused?

No, I'm worried about the opposite: Someone running (the equivalent of)
'ip link set dev eth0 xdp off', and then wondering why all resources
aren't freed.

I do believe that the common case could be solved by a logic similar to
the one I proposed, though:

>> Hmm, but I guess it could do that anyway; so maybe what we need is just
>> a "try to find all pinned maps of this program" function? That could
>> then to something like:
>> 
>> - Get the maps IDs and names of all maps attached to that program from
>>    the kernel.
>> 
>> - Look for each map name in /sys/fs/bpf
>> 
>> - If a pinned map with the same name exists, compare the IDs, and unlink
>>    if they match
>> 
>> I don't suppose it'll be possible to do all that in a race-free manner,
>> but that would go for any use of unlink() unless I'm missing something?