bpf: Introduce bpf_per_cpu_ptr()

Add bpf_per_cpu_ptr() to help bpf programs access percpu vars. bpf_per_cpu_ptr() has the same semantic as per_cpu_ptr() in the kernel except that it may return NULL. This happens when the cpu parameter is out of range. So the caller must check the returned value.

Hao Luo committed 6 years ago

Commit eaa6bcb1 parent 2c2f6ab8 files · +132 −13Browse files

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tools/include/uapi/linux/bpf.h+18−0

@@ -3686,6 +3686,23 @@ union bpf_attr { · 3685 unmodified lines
3686	3686	* Return
3687	3687	* The helper returns TC_ACT_REDIRECT on success or
3688	3688	* TC_ACT_SHOT on error.
	3689	+ *
	3690	+ * void bpf_per_cpu_ptr(const void percpu_ptr, u32 cpu)
	3691	+ * Description
	3692	+ * Take a pointer to a percpu ksym, percpu_ptr, and return a
	3693	+ * pointer to the percpu kernel variable on cpu. A ksym is an
	3694	+ * extern variable decorated with '__ksym'. For ksym, there is a
	3695	+ * global var (either static or global) defined of the same name
	3696	+ * in the kernel. The ksym is percpu if the global var is percpu.
	3697	+ * The returned pointer points to the global percpu var on cpu.
	3698	+ *
	3699	+ * bpf_per_cpu_ptr() has the same semantic as per_cpu_ptr() in the
	3700	+ * kernel, except that bpf_per_cpu_ptr() may return NULL. This
	3701	+ * happens if cpu is larger than nr_cpu_ids. The caller of
	3702	+ * bpf_per_cpu_ptr() must check the returned value.
	3703	+ * Return
	3704	+ * A pointer pointing to the kernel percpu variable on cpu, or
	3705	+ * NULL, if cpu is invalid.
3689	3706	*/
3690	3707	#define __BPF_FUNC_MAPPER(FN) \
3691	3708	FN(unspec), \
@@ -3841,6 +3858,7 @@ union bpf_attr { · 149 unmodified lines
3841	3858	FN(seq_printf_btf), \
3842	3859	FN(skb_cgroup_classid), \
3843	3860	FN(redirect_neigh), \
	3861	+ FN(bpf_per_cpu_ptr), \
3844	3862	/* */
3845	3863
3846	3864	/* integer value in 'imm' field of BPF_CALL instruction selects which helper