Hi, I am preparing for qp-trie v4, but I need some help on how to support variable-sized key in bpf syscall. The implementation of qp-trie needs to distinguish between dynptr key from bpf program and variable-sized key from bpf syscall. In v3, I added a new dynptr type: BPF_DYNPTR_TYPE_USER for variable-sized key from bpf syscall [0], so both bpf program and bpf syscall will use the same type to represent the variable-sized key, but Andrii thought ptr+size tuple was simpler and would be enough for user APIs, so in v4, the type of key for bpf program and syscall will be different. One way to handle that is to add a new parameter in .map_lookup_elem()/.map_delete_elem()/.map_update_elem() to tell whether the key comes from bpf program or syscall or introduce new APIs in bpf_map_ops for variable-sized key related syscall, but I think it will introduce too much churn. Considering that the size of bpf_dynptr_kern is 8-bytes aligned, so I think maybe I could reuse the lowest 1-bit of key pointer to tell qp-trie whether or not it is a bpf_dynptr_kern or a variable-sized key pointer from syscall. For bpf_dynptr_kern, because it is 8B-aligned, so its lowest bit must be 0, and for variable-sized key from syscall, I could allocated a 4B-aligned pointer and setting the lowest bit as 1, so qp-trie can distinguish between these two types of pointer. The question is that I am not sure whether the idea above is a good one or not. Does it sound fragile ? Or is there any better way to handle that ? Regards
