> In the process of updating packet capture to take a filter program, there
> is one open question about API/ABI.
>
> The example is:
>
> int
> rte_pdump_enable(uint16_t port, uint16_t queue, uint32_t flags,
> struct rte_ring *ring,
> struct rte_mempool *mp,
> void *filter);
>
> For the new version want to add ability to pass a BPF (classic) program
> from libcap. This is described in most pcap API's as "struct bpf_program".
>
> The filter parameter was left as a placeholder, but in typical YAGNI
> fashion. When we do need to use it, it is not going to work out.
>
> Since the existing filter argument was never used, there are a bunch
> of options (in order from best to worse).
>
> 1. Introduce new API which takes a filter.
>
> int
> rte_pdump_enable_bpf(uint16_t port, uint16_t queue, uint32_t flags,
> struct rte_ring *ring,
> struct rte_mempool *mp,
> const struct bpf_program *filter);
>
> The old API is just the same as calling new API with NULL as filter.
> This solution is safe but adds minor bloat.
>
> 2. Use API versioning. This solves the ABI problem but it is still
> an API breakage since program that was passing junk would still
> not compile.
>
> 3. Change the function signature of existing API. This risks breaking
> at compile time some program that was passing some other value.
> Similarly, a program could have passed garbage, we never checked.
>
> 4. Keep existing function signature, but be type unsafe.
> This keeps API, but still is ABI breakage for programs that passed
> garbage. Plus C is unsafe enough already.
>
My preference is probably #4, with some extra changes:
make actual type for 'filter' be determined by flags,
something like:
enum {
RTE_PDUMP_FLAG_RX = 1, /* receive direction */
RTE_PDUMP_FLAG_TX = 2, /* transmit direction */
+ RTE_PDUMP_FLAG_CBPF = 4, /* filter points to struct bpf_program */
/* both receive and transmit directions */
RTE_PDUMP_FLAG_RXTX = (RTE_PDUMP_FLAG_RX|RTE_PDUMP_FLAG_TX)
};
