On Tue, Jun 3, 2025 at 2:09 PM Song Liu [off-list ref] wrote:

On Tue, Jun 3, 2025 at 11:40 AM Andrii Nakryiko
[off-list ref] wrote:
[...]

quoted

quoted

+__bpf_kfunc struct path *bpf_iter_path_next(struct bpf_iter_path *it)
+{
+       struct bpf_iter_path_kern *kit = (void *)it;
+       struct path root = {};
+
+       if (!path_walk_parent(&kit->path, &root))
+               return NULL;
+       return &kit->path;
+}
+
+__bpf_kfunc void bpf_iter_path_destroy(struct bpf_iter_path *it)
+{
+       struct bpf_iter_path_kern *kit = (void *)it;
+
+       path_put(&kit->path);

note, destroy() will be called even if construction of iterator fails
or we exhausted iterator. So you need to make sure that you have
bpf_iter_path state where you can detect that there is no path present
and skip path_put().

In bpf_iter_path_next(), when path_walk_parent() returns false, we
still hold reference to kit->path, then _destroy() will release it. So we
should be fine, no?

you still need to handle iterators that failed to be initialized,
though? And one can argue that if path_walk_parent() returns false, we
need to put that last path before returning NULL, no?

Thanks,
Song

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+}
+
+__bpf_kfunc_end_defs();

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a7d6e0c5928b..45b45cdfb223 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c

@@ -7036,6 +7036,10 @@ BTF_TYPE_SAFE_TRUSTED_OR_NULL(struct socket) {
        struct sock *sk;
 };

+BTF_TYPE_SAFE_TRUSTED_OR_NULL(struct path) {
+       struct dentry *dentry;
+};
+
 static bool type_is_rcu(struct bpf_verifier_env *env,
                        struct bpf_reg_state *reg,
                        const char *field_name, u32 btf_id)

@@ -7076,6 +7080,7 @@ static bool type_is_trusted_or_null(struct bpf_verifier_env *env,
                                    const char *field_name, u32 btf_id)
 {
        BTF_TYPE_EMIT(BTF_TYPE_SAFE_TRUSTED_OR_NULL(struct socket));
+       BTF_TYPE_EMIT(BTF_TYPE_SAFE_TRUSTED_OR_NULL(struct path));

        return btf_nested_type_is_trusted(&env->log, reg, field_name, btf_id,
                                          "__safe_trusted_or_null");
--

2.47.1