blkcg_activate_policy(9)

✨ blkcg_activate_policy(9) ✨

okay so bestie, welcome to the kernel API manual page for blkcg_activate_policy 💅 you're gonna do great, i promise.

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🦋 NAME 🦋

blkcg_activate_policy — activate a blkcg policy on a gendisk

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🌸 SYNOPSIS 🌸

int blkcg_activate_policy (struct gendisk *disk , const struct
       blkcg_policy *pol );

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💖 ARGUMENTS 💖

• disk — the gendisk you care about, your main character 🫶
• pol — the blkcg policy you wanna activate, slay

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🎀 DESCRIPTION 🎀

So the whole vibe here: you're activating pol on disk. That's it, that's the function. ✨

It requires GFP_KERNEL context, no cap. And disk goes through bypass mode to populate its blkgs with policy_data for pol. lowkey iconic behavior.

Activation happens with disk bypassed, so nobody would be accessing blkgs from the IO path — vibe check passed 💀 no one's touching them mid-update. Every blkg update is protected by both queue and blkcg locks, so that holding either lock and testing blkcg_policy_enabled is always enough for dereferencing policy data. That's the guarantee, periodt. 🔥

Also, heads up bestie: the caller is responsible for synchronizing [de]activations and policy [un]registerations. Not us. You. 🙈

Returns 0 on success, -errno on failure. Easy. 👑

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🌈 SEE ALSO 🌈

Kernel file ./block/blk-cgroup.c 💜 and honestly the whole friend group:

blkcg_css(9), blkg_free(9), bio_blkcg_css(9), blkcg_parent(9), blkg_alloc(9), blkg_lookup_create(9), blkcg_print_blkgs(9), __blkg_prfill_u64(9), blkg_conf_init(9), blkg_conf_open_bdev(9), blkg_conf_prep(9), blkg_conf_unprep(9), blkg_conf_close_bdev(9), blkcg_destroy_blkgs(9), blkcg_pin_online(9), blkcg_unpin_online(9), blkcg_css_offline(9), blkcg_deactivate_policy(9), blkcg_policy_register(9), blkcg_policy_unregister(9), blkcg_maybe_throttle_current(9), blkcg_schedule_throttle(9), blkcg_add_delay(9), blkg_tryget_closest(9), bio_associate_blkg_from_css(9), bio_associate_blkg(9), bio_clone_blkg_association(9)

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that's the whole page, bestie, you ate it up 💅✨ this one lives in ./block and the version/date on the tin is October 2026 — so like, future vibes fr fr 🦋 go forth and activate those policies, iykyk 🎀👑