css_tryget_online_from_dir(9)

💅 css_tryget_online_from_dir(9) — the Kernel API Manual, bestie edition

okay so this page is from the Kernel API Manual, section 9, and it's about grabbing a css off a cgroup dentry without, like, wrecking anything. no cap, it's lowkey one of those tiny helper functions that ate and left no crumbs. 🫶

---

✨ NAME ✨

css_tryget_online_from_dir — literally get the corresponding css from a cgroup dentry 💖

---

🌸 SYNOPSIS 🌸

struct cgroup_subsys_state * css_tryget_online_from_dir (struct dentry
*dentry , struct cgroup_subsys *ss );

like that's the whole function signature, she's on one line and she's iconic ✨

---

🎀 ARGUMENTS 🎀

• dentry — the directory dentry you're interested in 👀 literally the one you care about
• ss — the subsystem you're interested in 💅

---

🦋 DESCRIPTION 🦋

so here's the vibe check: if dentry is a directory for a cgroup that has ss enabled on it, the function tries to get the corresponding css and hands it back to you. slay. 🎀

but listen — if that css doesn't exist, or if it can't be pinned, you don't get a css, you get an ERR_PTR value. 👑 that's the whole deal. not me warning you about the error path, but also, like, yes i am. 💀

---

🌈 SEE ALSO 🌈

this is the part where she name-drops literally everyone at the function party, Kernel file ./kernel/cgroup/cgroup.c and all her sisters, fr fr:

cgroup_ssid_enabled(9), cgroup_on_dfl(9), cgroup_e_css_by_mask(9), cgroup_e_css(9), cgroup_get_e_css(9), __cgroup_task_count(9), cgroup_task_count(9), for_each_css(9), do_each_subsys_mask(9), css_set_populated(9), css_update_populated(9), css_set_update_populated(9), css_set_move_task(9), compare_css_sets(9), find_existing_css_set(9), allocate_cgrp_cset_links(9), link_css_set(9), find_css_set(9), cgroup_file_mode(9), cgroup_calc_subtree_ss_mask(9), cgroup_kn_unlock(9), cgroup_kn_lock_live(9), css_clear_dir(9), css_populate_dir(9), cgroup_attach_lock(9), cgroup_attach_unlock(9), cgroup_migrate_add_task(9), cgroup_taskset_first(9), cgroup_taskset_next(9), cgroup_migrate_execute(9), cgroup_migrate_vet_dst(9), cgroup_migrate_finish(9), cgroup_migrate_add_src(9), cgroup_migrate_prepare_dst(9), cgroup_migrate(9), cgroup_attach_task(9), cgroup_update_dfl_csses(9), cgroup_lock_and_drain_offline(9), cgroup_save_control(9), cgroup_propagate_control(9), cgroup_restore_control(9), cgroup_apply_control_enable(9), cgroup_apply_control_disable(9), cgroup_apply_control(9), cgroup_finalize_control(9), cgroup_enable_threaded(9), cgroup_tryget_css(9), cgroup_addrm_files(9), cgroup_rm_cftypes(9), cgroup_add_cftypes(9), cgroup_add_dfl_cftypes(9), cgroup_add_legacy_cftypes(9), cgroup_file_notify(9), cgroup_file_show(9), css_next_child(9), css_next_descendant_pre(9), css_rightmost_descendant(9), css_next_descendant_post(9), css_has_online_children(9), css_task_iter_advance_css_set(9), css_task_iter_start(9), css_task_iter_next(9), css_task_iter_end(9), css_create(9), kill_css_sync(9), kill_css_finish(9), cgroup_destroy_locked(9), cgroup_init_early(9), cgroup_init(9), cgroup_fork(9), cgroup_v1v2_get_from_file(9), cgroup_get_from_file(9), cgroup_css_set_fork(9), cgroup_css_set_put_fork(9), cgroup_can_fork(9), cgroup_cancel_fork(9), cgroup_post_fork(9), cgroup_task_exit(9), css_from_id(9), cgroup_get_from_path(9), cgroup_v1v2_get_from_fd(9), cgroup_get_from_fd(9), cgroup_parse_float(9)

like… the whole group chat showed up. 💜

---

bestie reminder: this page lives in ./kernel/cgroup, and the date on it is October 2026 — so yeah, she's a Kernel API Manual girlie through and through. 🧚 drop a 🍓 in the chat for css_tryget_online_from_dir(9), periodt. 💅✨