user_regset_set_fn(9)

✨ user_regset_set_fn(9) ✨

okay so real talk, this is a page from the Kernel API Manual, bestie, and it's about user_regset_set_fn — the callback type that lives in &struct user_regset. buckle up, it's shorter than your attention span but every word eats 💅

---

🌸 NAME 🌸

user_regset_set_fn — literally the type of the @set function in &struct user_regset. that's it, that's the name 🎀

---

✨ SYNOPSIS ✨

typedef int user_regset_set_fn (struct task_struct *target , const
       struct user_regset *regset , unsigned int pos , unsigned int count ,
       const void *kbuf , const void __user *ubuf );

like, look at her. six params, returns an int, absolute main character energy 👑

---

🦋 ARGUMENTS 🦋

• target — the thread being examined. yes, the actual thread, she's the subject of the whole investigation 🔍
• regset — the regset being examined. the one under the microscope 🧚
• pos — offset into the regset data you're accessing, measured in bytes
• count — how much data you're copying, also in bytes
• kbuf — if it's not NULL, this is a kernel-space pointer to copy from 🫶
• ubuf — if kbuf is NULL, then this is the user-space pointer you copy from

---

💖 DESCRIPTION 💖

So the vibe here is: store register values. that's the job. that's the whole assignment ✍️

Return 0 on success. and if it fails? the usual failure returns are -EIO or -ENODEV — those are the ones that show up most, no cap 💀

the pos and count values are in bytes, but heads up, they must be properly aligned. not optional, not a suggestion, it's giving strict 😭

here's the branch logic so you don't fumble it:

• if kbuf is non-null, that buffer gets used and ubuf is ignored. sorry ubuf, you're benched 🙈
• if kbuf is NULL, then ubuf gives you a userland pointer to access directly — and in that case an -EFAULT return value is possible. so watch for it 👀

lowkey important: alignment on pos and count is a real requirement, not a vibe check you can skip ⚠️

---

🎀 SEE ALSO 🎀

Kernel file ./include/linux/regset.h — go read it, it's iconic:

• user_regset_active_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)

---

and that's the whole page bestie!! 💜 this one came from ./include/linux, dated October 2026 — so yeah, mark your calendar, the kernel source and that date are literally right there at the bottom, slay ⭐🌈