make_vfsgid(9)

✨ make_vfsgid(9) ✨

okay so bestie, welcome to the Kernel API Manual page for make_vfsgid — she's a section 9 function and she's literally here to map a filesystem kgid according to an idmapping 💅

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🌸 NAME 🌸

make_vfsgid — map a filesystem kgid according to an idmapping 🫶

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🎀 SYNOPSIS 🎀

vfsgid_t make_vfsgid (struct mnt_idmap *idmap , struct user_namespace
*fs_userns , kgid_t kgid );

like, three args, no drama ✨

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🦋 ARGUMENTS 🦋

• idmap — the mount's idmapping 👑 this is the one we're remapping into.
• fs_userns — the filesystem's idmapping 🌈 this is where the kgid is coming from.
• kgid — the actual kgid to be mapped 🍓 the little guy getting translated.

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💖 DESCRIPTION 💖

Take a kgid and remap it from fs_userns into idmap. Use this function when you're preparing a kgid to be reported to userspace — that's the whole vibe, that's the assignment 💅

Now the fast paths, because she's efficient:

• If initial_idmapping determines that this is not an idmapped mount, we can simply return kgid unchanged. no cap, nothing to do, we're done 🎀
• If initial_idmapping tells us that the filesystem is not mounted with an idmapping, we know the value of kgid won't change when calling from_kgid, so we can simply retrieve the value via __kgid_val directly 🔥 lowkey a shortcut, highkey correct.

bestie please note: initial_idmapping is the vibe check that decides which path we take — don't sleep on it 🙈

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⭐ RETURN ⭐

kgid mapped according to idmap. 💖

But — and this is the important part — if kgid has no mapping in either idmap or fs_userns, then INVALID_GID is returned. 😭 that's the sad path, that's the "she doesn't know her" path.

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🌈 SEE ALSO 🌈

Kernel file ./fs/mnt_idmapping.c, plus the whole friend group:

• initial_idmapping(9)
• make_vfsuid(9)
• from_vfsuid(9)
• from_vfsgid(9)
• vfsgid_in_group_p(9)
• mnt_idmap_get(9)
• mnt_idmap_put(9)

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and that's the page, bestie!! 🧚 this one lives in ./fs and she's dated October 2026 — slay, go map some gids responsibly 💜