The bpfilter subsystem, along with its
“user-mode blobs” infrastructure, attracted a lot of attention when it was
merged for the 4.18 kernel in 2018. Since then, however, development in
this effort has been, to put it charitably, subdued. Now, two years after
its merging, bpfilter may be in danger of being removed from the kernel as
a failed experiment.

Source: LWN.net – [$] Rethinking bpfilter and user-mode helpers