user_regset_active_fn(9)

💅 user_regset_active_fn(9)

okay so bestie, you've stumbled into the Kernel API Manual and this one is about a little typedef called user_regset_active_fn — it's the type of the @active function inside &struct user_regset. iykyk 🫶

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✨ SYNOPSIS ✨

typedef int user_regset_active_fn (struct task_struct *target , const
       struct user_regset *regset );

like, that's the whole signature. short king behavior honestly 👑

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🎀 ARGUMENTS 🎀

• target — the thread we're being nosy about and examining 👀
• regset — the regset we're examining, periodt

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🌸 DESCRIPTION 🌸

ok so the vibe check here is: what does your implementation return? and the answer depends, no cap 💁‍♀️

• Return -ENODEV if it's not available on the hardware that was found. it's giving "not supported on this ✨silicon✨" 😭
• Return 0 if there's no interesting state in this thread. nothing to see here bestie.
• Return >0 — that number being the number of size units of interesting state. so like, >0 = there is tea 🍓

and here's the important bit, so don't skip it: any get call that fetches state beyond that number will see the default initialization state for this data. which means — huge — a caller that already knows what the default state is need not copy it all out. efficiency slay 🔥

🫶 important caveat: this call is optional. the pointer is NULL if there's no inexpensive check to yield a value < n. so if you see NULL, that's not a bug, that's just the design, bestie.

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👑 SEE ALSO 👑

Kernel file ./include/linux/regset.h, plus the whole friend group:

• user_regset_set_fn(9)
• user_regset_writeback_fn(9)
• struct user_regset(9)
• struct user_regset_view(9)
• task_user_regset_view(9)
• copy_regset_from_user(9)

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ok that's the whole page, mwah 💋 it lives in ./include/linux, and this lil manual page was brought to you by October 2026 — see you in the next group chat, bestie 🦋✨🎀