On Tue, Jun 3, 2025 at 4:20 PM Song Liu [off-list ref] wrote:

On Tue, Jun 3, 2025 at 2:45 PM Andrii Nakryiko
[off-list ref] wrote:

quoted

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

quoted

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?

kit->path is zero'ed on initialization failures, so we can path_put() it
safely. For _next() returns NULL case, we can either put kit->path
in _destroy(), which is the logic now, or put kit->path in the last
_next() call and make _destroy() a no-op in that case. I don't have
a strong preference either way.

I didn't realize path_put() is a no-op for zeroed-out struct path. I'd
probably leave a comment for future selves, I don't have strong
preference otherwise.

Thanks,
Song