tools/lib/bpf/bpf_helpers.h

Source file repositories/reference/linux-study-clean/tools/lib/bpf/bpf_helpers.h

File Facts

System
Linux kernel
Corpus path
tools/lib/bpf/bpf_helpers.h
Extension
.h
Size
16601 bytes
Lines
447
Domain
Support Tooling And Documentation
Bucket
tools
Inferred role
Support Tooling And Documentation: implementation source
Status
source implementation candidate

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

Detected Declarations

Annotated Snippet

* bpf_for_each(cgroup, cg, parent_cg, CG_ITER_CHILDREN) {
 *     bpf_printk("Child cgroup id = %d", cg->cgroup_id);
 *     if (cg->cgroup_id == 123)
 *         break;
 * }
 *
 * I.e., it looks almost like high-level for each loop in other languages,
 * supports continue/break, and is verifiable by BPF verifier.
 *
 * For iterating integers, the difference between bpf_for_each(num, i, N, M)
 * and bpf_for(i, N, M) is in that bpf_for() provides additional proof to
 * verifier that i is in [N, M) range, and in bpf_for_each() case i is `int
 * *`, not just `int`. So for integers bpf_for() is more convenient.
 *
 * Note: this macro relies on C99 feature of allowing to declare variables
 * inside for() loop, bound to for() loop lifetime. It also utilizes GCC
 * extension: __attribute__((cleanup(<func>))), supported by both GCC and
 * Clang.
 */
#define bpf_for_each(type, cur, args...) for (							\
	/* initialize and define destructor */							\
	struct bpf_iter_##type ___it __attribute__((aligned(8), /* enforce, just in case */,	\
						    cleanup(bpf_iter_##type##_destroy))),	\
	/* ___p pointer is just to call bpf_iter_##type##_new() *once* to init ___it */		\
			       *___p __attribute__((unused)) = (				\
					bpf_iter_##type##_new(&___it, ##args),			\
	/* this is a workaround for Clang bug: it currently doesn't emit BTF */			\
	/* for bpf_iter_##type##_destroy() when used from cleanup() attribute */		\
					(void)bpf_iter_##type##_destroy, (void *)0);		\
	/* iteration and termination check */							\
	(((cur) = bpf_iter_##type##_next(&___it)));						\
)
#endif /* bpf_for_each */

#ifndef bpf_for
/* bpf_for(i, start, end) implements a for()-like looping construct that sets
 * provided integer variable *i* to values starting from *start* through,
 * but not including, *end*. It also proves to BPF verifier that *i* belongs
 * to range [start, end), so this can be used for accessing arrays without
 * extra checks.
 *
 * Note: *start* and *end* are assumed to be expressions with no side effects
 * and whose values do not change throughout bpf_for() loop execution. They do
 * not have to be statically known or constant, though.
 *
 * Note: similarly to bpf_for_each(), it relies on C99 feature of declaring for()
 * loop bound variables and cleanup attribute, supported by GCC and Clang.
 */
#define bpf_for(i, start, end) for (								\
	/* initialize and define destructor */							\
	struct bpf_iter_num ___it __attribute__((aligned(8), /* enforce, just in case */	\
						 cleanup(bpf_iter_num_destroy))),		\
	/* ___p pointer is necessary to call bpf_iter_num_new() *once* to init ___it */		\
			    *___p __attribute__((unused)) = (					\
				bpf_iter_num_new(&___it, (start), (end)),			\
	/* this is a workaround for Clang bug: it currently doesn't emit BTF */			\
	/* for bpf_iter_num_destroy() when used from cleanup() attribute */			\
				(void)bpf_iter_num_destroy, (void *)0);				\
	({											\
		/* iteration step */								\
		int *___t = bpf_iter_num_next(&___it);						\
		/* termination and bounds check */						\
		(___t && ((i) = *___t, (i) >= (start) && (i) < (end)));				\
	});											\
)
#endif /* bpf_for */

#ifndef bpf_repeat
/* bpf_repeat(N) performs N iterations without exposing iteration number
 *
 * Note: similarly to bpf_for_each(), it relies on C99 feature of declaring for()
 * loop bound variables and cleanup attribute, supported by GCC and Clang.
 */
#define bpf_repeat(N) for (									\
	/* initialize and define destructor */							\
	struct bpf_iter_num ___it __attribute__((aligned(8), /* enforce, just in case */	\
						 cleanup(bpf_iter_num_destroy))),		\
	/* ___p pointer is necessary to call bpf_iter_num_new() *once* to init ___it */		\
			    *___p __attribute__((unused)) = (					\
				bpf_iter_num_new(&___it, 0, (N)),				\
	/* this is a workaround for Clang bug: it currently doesn't emit BTF */			\
	/* for bpf_iter_num_destroy() when used from cleanup() attribute */			\
				(void)bpf_iter_num_destroy, (void *)0);				\
	bpf_iter_num_next(&___it);								\
	/* nothing here  */									\
)
#endif /* bpf_repeat */

#endif

Annotation

Implementation Notes