from_kgid(9)

💖 from_kgid — the Kernel API Manual, bestie edition 🎀

okay so picture this: you're deep in the kernel, you've got a kgid (that's the kernel's own internal gid, the ✨real✨ one) and you need to hand it to userspace in somebody's user namespace. That's literally this function. It's the glow-up translator between kernelspace and your targ namespace, and honestly? iconic.

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🌸 SYNOPSIS 🌸

gid_t from_kgid (struct user_namespace *targ , kgid_t kgid );

no cap, that's the whole signature. two args, one gid_t coming back at you 🫶

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🦋 ARGUMENTS 🦋

• targ — the struct user_namespace * you want a gid in. like, where do you want this gid to live? that one. ✨
• kgid — the kernel internal gid you're starting with (kgid_t). the raw material, the before picture 💅

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💜 DESCRIPTION 💜

So what happens is: it maps kgid into the user namespace that targ points at, and then returns the resulting gid to you. That's it. That's the function. 🎀

There is always a mapping into the initial user_namespace — so like, the original namespace never ghosts you, that mapping is guaranteed to be there, fr fr.

⚠️ but bestie, listen: if kgid has no mapping in targ, you don't get a nice value back — you get (gid_t)-1. that's your "nope, not found" signal, so check for it. lowkey important. 🫶

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🌈 SEE ALSO 🌈

the kernel file in question is ./kernel/user_namespace.c, and if you're gonna be messing with ids and namespaces, you'll want the whole bestie squad:

• make_kuid(9)
• from_kuid(9)
• from_kuid_munged(9)
• make_kgid(9)
• from_kgid_munged(9)
• make_kprojid(9)
• from_kprojid(9)
• from_kprojid_munged(9)
• verify_root_map(9)

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alright that's the page 💅 this lil slice of kernel API lives in ./kernel, it's the October 2026 vibes, and the whole thing is filed under from_kgid(9) — go map those gids, queen 👑✨