> -----Original Message-----
> From: Stephen Hemminger <step...@networkplumber.org>
> Sent: Sunday, January 7, 2024 7:59 PM
> To: dev@dpdk.org
> Cc: arshdeep.k...@intel.com; Gowda, Sandesh <sandesh.go...@intel.com>;
> Reshma Pattan <reshma.pat...@intel.com>
> Subject: Issues around packet capture when secondary process is doing rx/tx
>
> I have been looking at a problem reported by Sandesh where packet capture
> does not work if rx/tx burst is done in secondary process.
>
> The root cause is that existing rx/tx callback model just doesn't work unless
> the
> process doing the rx/tx burst calls is the same one that registered the
> callbacks.
This is not specific to packet capture. This is a generic problem and we should
look to solve it generically.
>
> An example sequence would be:
> 1. dumpcap (or pdump) as secondary tells pdump in primary to register
> callback
> 2. secondary process calls rx_burst.
> 3. rx_burst sees the callback but it has pointer pdump_rx which is not
> necessarily
> at same location in primary and secondary process.
> 4. indirect function call in secondary to bad location likely causes
> crash.
>
> Some possible workarounds.
> 1. Keep callback list per-process: messy, but won't crash. Capture won't
> work
> without other changes. In this primary would register callback, but
> secondaries
> would not use them in rx/tx burst.
>
> 2. Replace use of rx/tx callback in pdump with change to rte_ethdev to
> have
> a capture flag. (i.e. don't use indirection). Likely ABI problems.
> Basically, ignore the rx/tx callback mechanism. This is my
> preferred
> solution.
>
> 3. Some fix up mechanism (in EAL mp support?) to have each process
> fixup
> its callback mechanism.
Yes, would prefer this. Let the application call additional APIs to register
the call backs in secondary process.
>
> 4. Do something in pdump_init to register the callback in same process
> context
> (probably need callbacks to be per-process). Would mean callback is
> always
> on independent of capture being enabled.
>
> 5. Get rid of indirect function call pointer, and replace it by index
> into
> a static table of callback functions. Every process would have
> same code
> (in this case pdump_rx) but at different address. Requires all
> callbacks
> to be statically defined at build time.
>
> The existing rx/tx callback is not safe id rx/tx burst is called from
> different
> process than where callback is registered.
>
