write_cgroup_file_parent(9)

✨ write_cgroup_file_parent(9) ✨

okay bestie, so this is a page from the Kernel API Manual and it's literally called write_cgroup_file_parent — and yes, it does exactly what it says on the tin: it writes to a cgroup file over in the parent process's workdir 💅

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🌸 SYNOPSIS 🌸

int write_cgroup_file_parent (const char *relative_path , const char
*file , const char *buf );

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🎀 ARGUMENTS 🎀

• relative_path — the cgroup path, and it's relative to the parent process workdir (like, do not come at it with an absolute path, she's a relative girlie 🦋)
• file — the name of the file in cgroupfs you wanna write to 📝
• buf — the buffer holding the stuff you're writing to that file 🫶

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💖 DESCRIPTION 💖

So the whole vibe is: you write to a file in the given cgroup's directory, and that directory is hanging out under the parent process workdir. That's it, that's the job ✨

If it works out, 0 is returned. Iconic behavior, no notes. 👑

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🌈 SEE ALSO 🌈

Like, the source of truth is the kernel file ./tools/testing/selftests/bpf/cgroup_helpers.c — go read her, she ate 💅

And then there's the whole friend group:

• enable_controllers(9)
• write_cgroup_file(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)
• create_and_get_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)

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bestie please note: this page is living in ./tools/testing/selftests/bpf and it's dated October 2026 — so like, mark your calendar, she's from the future 🕰️✨

okay that's the whole page, ily, go write some cgroup files responsibly 💜🧚