cgroup_get_e_css(9)

💖 cgroup_get_e_css(9) 💖

okay so this is a page straight out of the Kernel API Manual — yes, the Kernel API Manual, we're literally reading kernel docs for fun now, that's the energy 🧚✨ — and it's all about cgroup_get_e_css, which is a little function that finds you the right css. bestie, if you don't know what a css is yet, don't panic, we're getting there, i promise 🫶

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✨ NAME ✨

cgroup_get_e_css — get a cgroup's effective css for the specified subsystem 💅

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🌸 SYNOPSIS 🌸

struct cgroup_subsys_state * cgroup_get_e_css (struct cgroup *cgrp ,
struct cgroup_subsys *ss );

like look at that signature, it's giving "returns a pointer to a struct cgroup_subsys_state" and honestly? iconic. 🔥

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🎀 ARGUMENTS 🎀

• cgrp — the cgroup of interest 🫶 like, this is the cgroup you're curious about, the main character of this whole operation
• ss — the subsystem of interest 🦋 the specific subsystem you want the css for

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💜 DESCRIPTION 💜

okay so the whole vibe here: find and get the effective css of cgrp for ss. that's the mission. 🎯

and what even is an "effective css"?? glad you asked bestie — it's defined as the matching css of the nearest ancestor including self which has ss enabled. read that again. nearest ancestor. including self. the closest one that actually has ss turned on. 👑

and here's the part where it's literally so reassuring: if ss is not mounted on the hierarchy cgrp is on, the root css is returned, so this function always returns a valid css. always. no nulls, no drama, no "oops try again" 😭💖

⚠️ okay but listen — the returned css must be put using css_put. this is not optional, this is not a suggestion, this is the rule. you took a reference, you give it back. that's the whole deal. 🙈

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🌈 SEE ALSO 🌈

kernel file ./kernel/cgroup/cgroup.c — and then a whole friend group of functions, like genuinely this is the biggest group chat ever, we're listing everyone:

cgroup_ssid_enabled(9), cgroup_on_dfl(9), cgroup_e_css_by_mask(9), cgroup_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_tryget_online_from_dir(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, that's the whole friend group right there. no cap. 💀👑

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🌸 and that's the page!! 🌸

signed off from ./kernel/cgroup, dated October 2026, and yes this is cgroup_get_e_css(9) saying bye bestie — go css_put that reference, i'm watching 💅✨💖

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