CURPROC(9)

💅 curproc(9) — current processor, thread, and process 🦋

okay so this is a page from the Kernel Developer's Manual, bestie, and it's literally about three little things that tell you where you are and who you are inside the kernel. main character energy fr 💖

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✨ NAME ✨

curcpu, curlwp, curproc — current processor, thread, and process 🌸

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🎀 SYNOPSIS 🎀

#include <sys/proc.h>

struct cpu_info *
curcpu(void);

struct proc *curproc;
struct lwp *curlwp;

#include <sys/cpu.h>

bool
curcpu_stable(void);

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💅 DESCRIPTION 💅

okay so these three retrieve the current CPU, process, and thread (that's a lightweight process, aka LWP, iykyk) respectively — one for each, slay:

• curcpu() — returns a pointer to the struct cpu_info structure that represents the CPU the code calling it is running on. ✨

⚠️ bestie listen — the value of curcpu() is unstable and may be stale as soon as it is read unless the caller prevents preemption by raising the IPL (spl(9), mutex(9)), by disabling preemption (kpreempt_disable(9)), or by binding the thread to its CPU (curlwp_bind(9)). like, it literally expires on contact 😭

The function curcpu_stable() can be used in assertions (KASSERT(9)) to verify that curcpu() is stable in the current context. curcpu_stable() MUST NOT be used to make dynamic decisions about whether to query curcpu(). 🫶 like, assert with it, don't decide with it — that's the whole vibe check.

• curproc — yields a pointer to the struct proc structure representing the currently running process. 👑

The value of curproc is stable and does not change during execution except in machine-dependent logic to perform context switches, so it works like a global constant, not like a stateful procedure. no cap, it just is 💜

• curlwp — yields a pointer to the struct lwp structure representing the currently running thread. 🧚

The value of curlwp is stable and does not change during execution except in machine-dependent logic to perform context switches, so it works like a global constant, not like a stateful procedure. same energy, iconic behaviour 🌈

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🦋 SOURCE REFERENCES 🦋

• the curcpu() macro is defined in the machine-independent machine/cpu.h ✨
• the curproc macro is defined in sys/lwp.h
• the curlwp macro has a machine-independent definition in sys/lwp.h, but it may be overridden by machine/cpu.h, and must be overridden on architectures supporting multiprocessing and kernel preemption 🔥 (so on those archs, sys/lwp.h's version is not the final word — periodt)
• the curcpu_stable() function is defined in kern/subr_cpu.c 🍓

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👀 SEE ALSO 👀

• cpu_number(9)
• proc_find(9)

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okay that's the whole page, go off 💅 and yeah — this cutie came from Debian, dated July 8, 2023. mwah 🫶💖