Re: [RFC PATCH bpf-next 0/8] bpf_link observability APIs

[David Ahern <dsahern@gmail.com>]

On 4/3/20 6:09 PM, Andrii Nakryiko wrote:
> This patch series adds various observability APIs to bpf_link:
>   - each bpf_link now gets ID, similar to bpf_map and bpf_prog, by which
>     user-space can iterate over all existing bpf_links and create limited FD
>     from ID;
>   - allows to get extra object information with bpf_link general and
>     type-specific information;
>   - makes LINK_UPDATE operation allowed only for writable bpf_links and allows
>     to pin bpf_link as read-only file;
>   - implements `bpf link show` command which lists all active bpf_links in the
>     system;
>   - implements `bpf link pin` allowing to pin bpf_link by ID or from other
>     pinned path.
> 
> This RFC series is missing selftests and only limited amount of manual testing
> was performed. But kernel implementation is hopefully in a good shape and
> won't change much (unless some big issues are identified with the current
> approach). It would be great to get feedback on approach and implementation,
> before I invest more time in writing tests.
> 

The word 'ownership' was used over and over in describing the benefits
of bpf_link meaning a process owns a program at a specific attach point.
How does this set allow me to discover the pid of the process
controlling a specific bpf_link?