[PATCH v6 20/23] mbuf: remove and stop using rte marker fields

[Tyler Retzlaff]

On Tue, Feb 27, 2024 at 04:18:10PM +0100, David Marchand wrote:
> Hello Dodji,
> 
> On Tue, Feb 27, 2024 at 6:44 AM Tyler Retzlaff
> <roretzla at linux.microsoft.com> wrote:
> >
> > RTE_MARKER typedefs are a GCC extension unsupported by MSVC. Remove
> > RTE_MARKER fields from rte_mbuf struct.
> >
> > Maintain alignment of fields after removed cacheline1 marker by placing
> > C11 alignas(RTE_CACHE_LINE_MIN_SIZE).
> >
> > Update implementation of rte_mbuf_prefetch_part1() and
> > rte_mbuf_prefetch_part2() inline functions calculate pointer for
> > prefetch of cachline0 and cachline1 without using removed markers.
> >
> > Update static_assert of rte_mbuf struct fields to reference data_off and
> > packet_type fields that occupy the original offsets of the marker
> > fields.
> >
> > Signed-off-by: Tyler Retzlaff <roretzla at linux.microsoft.com>
> 
> This change is reported as a potential ABI change.
> 
> For the context, this patch
> https://patchwork.dpdk.org/project/dpdk/patch/1709012499-12813-21-git-send-email-roretzla@linux.microsoft.com/
> removes null-sized markers (those fields were using RTE_MARKER, see
> https://git.dpdk.org/dpdk/tree/lib/eal/include/rte_common.h#n583) from
> the rte_mbuf struct.
> I would argue this change do not impact ABI as the layout of the mbuf
> object is not impacted.

It isn't a surprise that the change got flagged because the 0 sized
fields being removed probably not something the checker understands.
So no ABI change just API break (as was requested).

> As reported by the CI:
> 
>   [C] 'function const rte_eth_rxtx_callback*
> rte_eth_add_first_rx_callback(uint16_t, uint16_t, rte_rx_callback_fn,
> void*)' at rte_ethdev.c:5768:1 has some indirect sub-type changes:
>     parameter 3 of type 'typedef rte_rx_callback_fn' has sub-type changes:
>       underlying type 'typedef uint16_t (typedef uint16_t, typedef
> uint16_t, rte_mbuf**, typedef uint16_t, typedef uint16_t, void*)*'
> changed:
>         in pointed to type 'function type typedef uint16_t (typedef
> uint16_t, typedef uint16_t, rte_mbuf**, typedef uint16_t, typedef
> uint16_t, void*)':
>           parameter 3 of type 'rte_mbuf**' has sub-type changes:
>             in pointed to type 'rte_mbuf*':
>               in pointed to type 'struct rte_mbuf' at rte_mbuf_core.h:470:1:
>                 type size hasn't changed
>                 4 data member deletions:
>                   'RTE_MARKER cacheline0', at offset 0 (in bits) at
> rte_mbuf_core.h:467:1
>                   'RTE_MARKER64 rearm_data', at offset 128 (in bits)
> at rte_mbuf_core.h:490:1
>                   'RTE_MARKER rx_descriptor_fields1', at offset 256
> (in bits) at rte_mbuf_core.h:517:1
>                   'RTE_MARKER cacheline1', at offset 512 (in bits) at
> rte_mbuf_core.h:598:1
>                 no data member change (1 filtered);
> 
> Error: ABI issue reported for abidiff --suppr
> /home/runner/work/dpdk/dpdk/devtools/libabigail.abignore
> --no-added-syms --headers-dir1 reference/usr/local/include
> --headers-dir2 install/usr/local/include
> reference/usr/local/lib/librte_ethdev.so.24.0
> install/usr/local/lib/librte_ethdev.so.24.1
> ABIDIFF_ABI_CHANGE, this change requires a review (abidiff flagged
> this as a potential issue).
> 
> Opinions?
> 
> Btw, I see no way to suppress this (except a global [suppress_type]
> name = rte_mbuf)...

I am unfamiliar with the ABI checker I'm afraid i have no suggestion to
offer. Maybe we can just ignore the failure for this one series when we
decide it is ready to be merged and don't suppress the checker?

> 
> 
> -- 
> David Marchand