On Fri, Feb 4, 2022 at 10:27 AM Hao Luo <haoluo@xxxxxxxxxx> wrote: > > > > > In our use case, we can't ask the users who create cgroups to do the > > > pinning. Pinning requires root privilege. In our use case, we have > > > non-root users who can create cgroup directories and still want to > > > read bpf stats. They can't do pinning by themselves. This is why > > > inheritance is a requirement for us. With inheritance, they only need > > > to mkdir in cgroupfs and bpffs (unprivileged operations), no pinning > > > operation is required. Patch 1-4 are needed to implement inheritance. > > > > > > It's also not a good idea in our use case to add a userspace > > > privileged process to monitor cgroupfs operations and perform the > > > pinning. It's more complex and has a higher maintenance cost and > > > runtime overhead, compared to the solution of asking whoever makes > > > cgroups to mkdir in bpffs. The other problem is: if there are nodes in > > > the data center that don't have the userspace process deployed, the > > > stats will be unavailable, which is a no-no for some of our users. > > > > The commit log says that there will be a daemon that does that > > monitoring of cgroupfs. And that daemon needs to mkdir > > directories in bpffs when a new cgroup is created, no? > > The kernel is only doing inheritance of bpf progs into > > new dirs. I think that daemon can pin as well. > > > > The cgroup creation is typically managed by an agent like systemd. > > Sounds like you have your own agent that creates cgroups? > > If so it has to be privileged and it can mkdir in bpffs and pin too ? > > Ah, yes, we have our own daemon to manage cgroups. That daemon creates > the top-level cgroup for each job to run inside. However, the job can > create its own cgroups inside the top-level cgroup, for fine grained > resource control. This doesn't go through the daemon. The job-created > cgroups don't have the pinned objects and this is a no-no for our > users. We can whitelist certain tracepoints to be sleepable and extend tp_btf prog type to include everything from prog_type_syscall. Such prog would attach to cgroup_mkdir and cgroup_release and would call bpf_sys_bpf() helper to pin progs in new bpffs dirs. We can allow prog_type_syscall to do mkdir in bpffs as well. This feature could be useful for similar monitoring/introspection tasks. We can write a program that would monitor bpf prog load/unload and would pin an iterator prog that would show debug info about a prog. Like cat /sys/fs/bpf/progs.debug shows a list of loaded progs. With this feature we can implement: ls /sys/fs/bpf/all_progs.debug/ and each loaded prog would have a corresponding file. The file name would be a program name, for example. cat /sys/fs/bpf/all_progs.debug/my_prog would pretty print info about 'my_prog' bpf program. This way the kernfs/cgroupfs specific logic from patches 1-4 will not be necessary. wdyt?
