Implement the first open-coded iterator type over a range of integers.
It's public API consists of:
- bpf_iter_num_new() constructor, which accepts [start, end) range
(that is, start is inclusive, end is exclusive).
- bpf_iter_num_next() which will keep returning read-only pointer to int
until the range is exhausted, at which point NULL will be returned.
If bpf_iter_num_next() is kept calling after this, NULL will be
persistently returned.
- bpf_iter_num_destroy() destructor, which needs to be called at some
point to clean up iterator state. BPF verifier enforces that iterator
destructor is called at some point before BPF program exits.
Note that `start = end = X` is a valid combination to setup an empty
iterator. bpf_iter_num_new() will return 0 (success) for any such
combination.
If bpf_iter_num_new() detects invalid combination of input arguments, it
returns error, resets iterator state to, effectively, empty iterator, so
any subsequent call to bpf_iter_num_next() will keep returning NULL.
BPF verifier has no knowledge that returned integers are in the
[start, end) value range, as both `start` and `end` are not statically
known and enforced: they are runtime values.
While the implementation is pretty trivial, some care needs to be taken
to avoid overflows and underflows. Subsequent selftests will validate
correctness of [start, end) semantics, especially around extremes
(INT_MIN and INT_MAX).
Similarly to bpf_loop(), we enforce that no more than BPF_MAX_LOOPS can
be specified.
bpf_iter_num_{new,next,destroy}() is a logical evolution from bounded
BPF loops and bpf_loop() helper and is the basis for implementing
ergonomic BPF loops with no statically known or verified bounds.
Subsequent patches implement bpf_for() macro, demonstrating how this can
be wrapped into something that works and feels like a normal for() loop
in C language.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230308184121.1165081-5-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
#define BPF_COMPLEXITY_LIMIT_INSNS 1000000 /* yes. 1M insns */
#define MAX_TAIL_CALL_CNT 33
-/* Maximum number of loops for bpf_loop */
-#define BPF_MAX_LOOPS BIT(23)
+/* Maximum number of loops for bpf_loop and bpf_iter_num.
+ * It's enum to expose it (and thus make it discoverable) through BTF.
+ */
+enum {
+ BPF_MAX_LOOPS = 8 * 1024 * 1024,
+};
#define BPF_F_ACCESS_MASK (BPF_F_RDONLY | \
BPF_F_RDONLY_PROG | \
BPF_F_TIMER_ABS = (1ULL << 0),
};
+/* BPF numbers iterator state */
+struct bpf_iter_num {
+ /* opaque iterator state; having __u64 here allows to preserve correct
+ * alignment requirements in vmlinux.h, generated from BTF
+ */
+ __u64 __opaque[1];
+} __attribute__((aligned(8)));
+
#endif /* _UAPI__LINUX_BPF_H__ */
.arg3_type = ARG_PTR_TO_STACK_OR_NULL,
.arg4_type = ARG_ANYTHING,
};
+
+struct bpf_iter_num_kern {
+ int cur; /* current value, inclusive */
+ int end; /* final value, exclusive */
+} __aligned(8);
+
+__diag_push();
+__diag_ignore_all("-Wmissing-prototypes",
+ "Global functions as their definitions will be in vmlinux BTF");
+
+__bpf_kfunc int bpf_iter_num_new(struct bpf_iter_num *it, int start, int end)
+{
+ struct bpf_iter_num_kern *s = (void *)it;
+
+ BUILD_BUG_ON(sizeof(struct bpf_iter_num_kern) != sizeof(struct bpf_iter_num));
+ BUILD_BUG_ON(__alignof__(struct bpf_iter_num_kern) != __alignof__(struct bpf_iter_num));
+
+ BTF_TYPE_EMIT(struct btf_iter_num);
+
+ /* start == end is legit, it's an empty range and we'll just get NULL
+ * on first (and any subsequent) bpf_iter_num_next() call
+ */
+ if (start > end) {
+ s->cur = s->end = 0;
+ return -EINVAL;
+ }
+
+ /* avoid overflows, e.g., if start == INT_MIN and end == INT_MAX */
+ if ((s64)end - (s64)start > BPF_MAX_LOOPS) {
+ s->cur = s->end = 0;
+ return -E2BIG;
+ }
+
+ /* user will call bpf_iter_num_next() first,
+ * which will set s->cur to exactly start value;
+ * underflow shouldn't matter
+ */
+ s->cur = start - 1;
+ s->end = end;
+
+ return 0;
+}
+
+__bpf_kfunc int *bpf_iter_num_next(struct bpf_iter_num* it)
+{
+ struct bpf_iter_num_kern *s = (void *)it;
+
+ /* check failed initialization or if we are done (same behavior);
+ * need to be careful about overflow, so convert to s64 for checks,
+ * e.g., if s->cur == s->end == INT_MAX, we can't just do
+ * s->cur + 1 >= s->end
+ */
+ if ((s64)(s->cur + 1) >= s->end) {
+ s->cur = s->end = 0;
+ return NULL;
+ }
+
+ s->cur++;
+
+ return &s->cur;
+}
+
+__bpf_kfunc void bpf_iter_num_destroy(struct bpf_iter_num *it)
+{
+ struct bpf_iter_num_kern *s = (void *)it;
+
+ s->cur = s->end = 0;
+}
+
+__diag_pop();
BTF_ID_FLAGS(func, bpf_rcu_read_unlock)
BTF_ID_FLAGS(func, bpf_dynptr_slice, KF_RET_NULL)
BTF_ID_FLAGS(func, bpf_dynptr_slice_rdwr, KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_iter_num_new, KF_ITER_NEW)
+BTF_ID_FLAGS(func, bpf_iter_num_next, KF_ITER_NEXT | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_iter_num_destroy, KF_ITER_DESTROY)
BTF_SET8_END(common_btf_ids)
static const struct btf_kfunc_id_set common_kfunc_set = {
BPF_F_TIMER_ABS = (1ULL << 0),
};
+/* BPF numbers iterator state */
+struct bpf_iter_num {
+ /* opaque iterator state; having __u64 here allows to preserve correct
+ * alignment requirements in vmlinux.h, generated from BTF
+ */
+ __u64 __opaque[1];
+} __attribute__((aligned(8)));
+
#endif /* _UAPI__LINUX_BPF_H__ */
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