vfsgid_has_fsmapping(9)

💅 vfsgid_has_fsmapping — check whether a vfsgid maps into the filesystem

okay so bestie, this is vfsgid_has_fsmapping(9) from the Kernel API Manual, and it's literally the "does this group ID even exist over here" check. tiny function, huge main character energy. let's go 🦋

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✨ SYNOPSIS ✨

bool vfsgid_has_fsmapping (struct mnt_idmap *idmap , struct
user_namespace *fs_userns , vfsgid_t vfsgid );

it returns a bool, it takes three things, and yes the spacing in that signature is exactly how it shipped — we don't fix, we don't merge, we just vibe 🎀

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🌸 ARGUMENTS 🌸

• idmap — the mount's idmapping. this is your mount's little translation dictionary, keep it close 🫶
• fs_userns — the filesystem's idmapping. this is the filesystem's dictionary, and it is a completely different dictionary, which is the whole plot of this function ngl
• vfsgid — the vfsgid to be mapped. the actual group id we're asking about 💅

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👑 DESCRIPTION 👑

so here's the tea: this function checks whether vfsgid has a mapping in the filesystem idmapping. that's it. that's the whole thing.

use this function to check whether the filesystem idmapping has a mapping for vfsgid. like, "does the filesystem have a seat for this gid at the table, or is it gonna get turned into the overflow id and have a bad time 😭"

it's a vibe check for gids. no cap, that's the function ✨

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🔥 RETURN 🔥

• true — vfsgid has a mapping in the filesystem. slay 💖
• false — it does not. it's giving unmapped 💀

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🌈 SEE ALSO 🌈

• Kernel file ./include/linux/mnt_idmapping.h — go read the header, it's iconic
• vfsuid_eq_kuid(9)
• vfsgid_eq_kgid(9)
• vfsuid_has_fsmapping(9)
• vfsuid_into_kuid(9)
• vfsgid_into_kgid(9)
• mapped_fsuid(9)
• mapped_fsgid(9)

the whole idmapping friend group fr fr, they all show up together 🧚

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lowkey reminder: this one asks the filesystem's idmapping, not the mount's. don't mix up your dictionaries or you will be so confused, iykyk 🙈

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okay that's the page!! this gem lives in ./include/linux, and the version tag on it is October 2026 — so mark your calendar bestie, and remember the page you just read was vfsgid_has_fsmapping(9) from the Kernel API Manual. periodt. 💜🦋✨