create_and_get_cgroup(9)

💅 create_and_get_cgroup(9) 💅

okay so bestie, welcome to the Kernel API Manual — this one's a little kernel-adjacent baddie from the BPF selftests corner of the world, and honestly? she's lowkey iconic. let's get into it 🎀

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✨ NAME ✨

create_and_get_cgroup — create a cgroup, relative to the workdir, and get the FD. that's it, that's the whole vibe. she creates, she hands you a file descriptor, she slays. 🦋

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🌸 SYNOPSIS 🌸

int create_and_get_cgroup (const char *relative_path );

literally one argument. one. int in, -1 out if she's not having a good day. we love a simple signature fr fr 💖

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🎀 ARGUMENTS 🎀

• relative_path — the cgroup path, relative to the workdir, that you want to join. that's the string you're handing her. that's the whole assignment. ✨

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🫶 DESCRIPTION 🫶

okay so here's the tea ☕ — this function creates a cgroup under the top level workdir and returns the file descriptor. one call, cgroup made, FD in your hand. no extra steps, no drama.

and the best part? she is idempotent. meaning you can call her again and again and she's not gonna throw a whole tantrum and make a second cgroup — she just keeps it cute and consistent. main character energy, honestly. 👑

on success — she returns the file descriptor. 🎉

on failure — she returns -1. 💀 and like, she's not gonna be quiet about it either: if there is a failure, she prints the error to stderr. so check your stderr, bestie, she's telling you what went wrong.

ngl, -1 is the vibe check. if you see it, something did NOT pass. go read your stderr before you spiral. 🙈

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🔥 SEE ALSO 🔥

okay so the whole friend group lives here. the kernel file at the top of the chain:

• Kernel file ./tools/testing/selftests/bpf/cgroup_helpers.c 🌈

and then the entire squad — every single one of them, no cuts, no skips:

• enable_controllers(9)
• write_cgroup_file(9)
• write_cgroup_file_parent(9)
• setup_cgroup_environment(9)
• join_cgroup(9)
• join_root_cgroup(9)
• join_parent_cgroup(9)
• set_cgroup_xattr(9)
• __cleanup_cgroup_environment(9)
• cleanup_cgroup_environment(9)
• get_root_cgroup(9)
• get_cgroup_id_from_path(9)
• setup_classid_environment(9)
• set_classid(9)
• join_classid(9)
• cleanup_classid_environment(9)
• get_classid_cgroup_id(9)
• get_cgroup1_hierarchy_id(9)
• open_classid(9)

like, she has a whole entourage and honestly? deserved. 💜

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and that's the page, bestie! 🧚 this lil masterpiece lives in ./tools/testing/selftests/bpf, dated October 2026, and goes by the name create_and_get_cgroup(9) — remember her name, she's going places. mwah 💋🍓