find_existing_css_set(9)

💅 NAME 💅

okay so bestie, welcome to the Kernel API Manual, section 9, cgroups territory — this page is all about find_existing_css_set, and what it does is literally right there in the name: init css array and find the matching css_set ✨

no cap, that's the whole job description. short, sweet, iconic 🎀

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🌸 SYNOPSIS 🌸

here's the signature, copy it exactly, don't freestyle it:

struct css_set * find_existing_css_set (struct css_set *old_cset ,
       struct cgroup *cgrp , struct cgroup_subsys_state **template );

three args, one pointer back out the door. the way that return type is a struct css_set *… yes ma'am 🫶

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🦋 ARGUMENTS 🦋

• old_cset — the css_set that we're using before the cgroup transition. so like, the vibe you're leaving behind 👋
• cgrp — the cgroup that we're moving into. the destination, the new home, the main character of this operation 🏠
• template — an out param for the new set of csses. ⚠️ and listen: it should be clear on entry. not "should probably", not "ideally" — clear on entry. so wipe it first, bestie, don't make it awkward 💀

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🌈 SEE ALSO 🌈

so there's a lot here, and i mean a lot — this page hangs out with basically the entire cgroup friend group. deep breath, here we go 💖

it all lives in the kernel file ./kernel/cgroup/cgroup.c, and the crew is:

• 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), 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 i said. the whole group chat 😭 and yes, every single one of them is a real (9) reference, i didn't skip a single bestie 💜

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aaand that's the page, babe 🎀 it comes from ./kernel/cgroup, dated October 2026, and the footer tag is find_existing_css_set(9) — same energy as the header, full circle, periodt 💅🌸