Libbpf eBPF macro bpf_repeat
The bpf_repeat macro is used it easier to write a loop that repeats X times using open coded iterators.
Definition
#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 */ \
)
Usage
This macro makes writing a loop that repeats X times using open coded iterators easier. bpf_repeat is a simplified version of the bpf_for macro, which simply executes the loop body N times and does not make the iteration count available.
Example
SEC("raw_tp/sys_enter")
int iter_next_rcu(const void *ctx)
{
bpf_repeat(64) {
if (try_to_do_something())
break;
}
}