On Fri, Mar 29, 2024 at 2:39 PM Tejun Heo tj@kernel.org wrote:
Hello,
On Fri, Mar 29, 2024 at 02:22:28PM +0100, Djalal Harouni wrote:
It would be easy at least for me if I just start with cgroupv2 and ensure that it has same available filenames as if we go through kernfs. Not a root cgroup node and maybe only freeze and kill for now that are part of cgroup_base_files.
So if I get it right, somehow like what I did but we endup with:
In bpf, cgroup was already acquired.
bpf_cgroup_knob_write(cgroup, "freeze", buf) |_ parse params -> lock cgroup_mutex -> cgroup_freeze() -> unlock
cgroup_freeze_write(struct kernfs_open_file *of, char *buf,...) |_ parse params -> cgroup_ref++ -> krnfs_active_ref-- -> -> lock cgroup_mutex -> cgroup_freeze() -> unlock + krnfs++ ...
Please let me know if I missed something.
I've thought about it a bit and I wonder whether a better way to do this is implementing this at the kernfs layer. Something like (hopefully with a better name):
s32 bpf_kernfs_knob_write(struct kernfs_node *dir, const char *knob, char *buf);
So, about the same, but takes kernfs_node directory instead of cgroup. This would make the interface useful for accessing sysfs knobs too which use similar conventions. For cgroup, @dir is just cgrp->kn and for sysfs it'd be kobj->sd. This way we can avoid the internal object -> path -> internal object ping-poinging while keeping the interface a lot more generic. What do you think?
And helpers like cgroup_freeze_write() will be refactored to take kernfs_node directly instead of kernfs_open_file? Makes sense to me. Sounds like a minimal amount of changes and flexible enough.