Hello, On 3/30/24 00:04, Alexei Starovoitov wrote: > On Fri, Mar 29, 2024 at 2:39 PM Tejun Heo <tj@xxxxxxxxxx> 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. Thank you Alexei, Tejun for the feedback. Will try to get back with a v2. One particular thing is the kernfs_open_file->mutex nests outside of the refcounting of kernfs_node, let's see. Thanks!
