[$] Monitoring mount operations

Amir Goldstein kicked off a session on monitoring mounts at the2023 Linux Storage, Filesystem,Memory-Management and BPF Summit. In particular, there are problemswhen trying to efficiently monitor "a very large number of mounts in amount namespace"; some user-space programs need an accurate view of themount tree without having to constantly parse /proc/mounts or thelike. There are a number of questions to be answered, including what the API should look like and what entity should be watchedin order to get notifications of new mount operations.