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

[David Marchand]

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.

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)...


-- 
David Marchand