On Mon, Apr 26, 2021 at 8:29 AM Christian Brauner
[off-list ref] wrote:

[...]

quoted

Have you considered accepting a cgroup fd to pidfd_send_signal and
realize this operation through this syscall? (Just asking as it may
prevent some of these consequences whereas bring other unclarities.)

That's semantically quite wrong on several fronts, I think.
pidfd_send_signal() operates on pidfds (and for a quirky historical
reason /proc/<pid> though that should die at some point). Making this
operate on cgroup fds is essentially implicit multiplexing which is
pretty nasty imho. In addition, this is a cgroup concept not a pidfd
concept.

What's your take on a new syscall cgroupfd_send_signal()? One
complexity would be potentially different semantics for v1 and v2.