Re: [PATCH v2] mbuf: dump Tx offload metadata

[David Marchand <david.marchand@redhat.com>]

On Tue, 4 Nov 2025 at 11:02, David Marchand <david.marchand@redhat.com> wrote:
>
> When debugging TSO and other checksum offloads, dumping the various
> l*_len fields and TSO segmentation size can be helpful.
>
> Example in OVS that dumps a mbuf on rte_eth_tx_prepare failure:
>
> Before:
> netdev_dpdk(pmd-c30/id:11)|DBG|dpdk0: First invalid packet:
> dump mbuf at 0x2201a916c0, iova=0x2200800580, buf_len=6864
>   pkt_len=6804, ol_flags=0x3114800000000102, nb_segs=1, port=65535, ptype=0
>   segment at 0x2201a916c0, data=0x22008005b2, len=6804, off=50, refcnt=1
>   Dump data at [0x22008005b2], len=6804
> ...
>
> After:
> netdev_dpdk(pmd-c30/id:11)|DBG|dpdk0: First invalid packet:
> dump mbuf at 0x2201a916c0, iova=0x2200800580, buf_len=6864, pkt_len=6804
>   outer_l2_len=14, outer_l3_len=40, l2_len=38, l3_len=40, l4_len=32
>   ol_flags=0x3114800000000102, nb_segs=1, port=65535, ptype=0
>   segment at 0x2201a916c0, data=0x22008005b2, len=6804, off=50, refcnt=1
>   Dump data at [0x22008005b2], len=6804
> ...
>
> Signed-off-by: David Marchand <david.marchand@redhat.com>
> ---
>  lib/mbuf/rte_mbuf.c | 41 +++++++++++++++++++++++++++++++++++++----
>  1 file changed, 37 insertions(+), 4 deletions(-)
>
> diff --git a/lib/mbuf/rte_mbuf.c b/lib/mbuf/rte_mbuf.c
> index 0d931c7a15..12710a59df 100644
> --- a/lib/mbuf/rte_mbuf.c
> +++ b/lib/mbuf/rte_mbuf.c
> @@ -750,10 +750,43 @@ rte_pktmbuf_dump(FILE *f, const struct rte_mbuf *m, unsigned dump_len)
>
>         __rte_mbuf_sanity_check(m, 1);
>
> -       fprintf(f, "dump mbuf at %p, iova=%#" PRIx64 ", buf_len=%u\n", m, rte_mbuf_iova_get(m),
> -               m->buf_len);
> -       fprintf(f, "  pkt_len=%u, ol_flags=%#"PRIx64", nb_segs=%u, port=%u",
> -               m->pkt_len, m->ol_flags, m->nb_segs, m->port);
> +       fprintf(f, "dump mbuf at %p, iova=%#" PRIx64 ", buf_len=%u, pkt_len=%u\n",
> +               m, rte_mbuf_iova_get(m), m->buf_len, m->pkt_len);
> +       if (m->ol_flags & RTE_MBUF_F_TX_OFFLOAD_MASK) {
> +               const char *sep = "";
> +
> +               fprintf(f, "  ");
> +               if (m->outer_l2_len != 0) {
> +                       fprintf(f, "%souter_l2_len=%u", sep, m->outer_l2_len);

One more round will be needed for MSVC (CI did not report it on v1,
some tests did not run..).
../lib/mbuf/rte_mbuf.c(760): error C2220: the following warning is
treated as an error
../lib/mbuf/rte_mbuf.c(760): warning C4477: 'fprintf' : format string
'%u' requires an argument of type 'unsigned int', but variadic
argument 2 has type 'const uint64_t'
../lib/mbuf/rte_mbuf.c(760): note: consider using '%llu' in the format string
../lib/mbuf/rte_mbuf.c(760): note: consider using '%Iu' in the format string
../lib/mbuf/rte_mbuf.c(760): note: consider using '%I64u' in the format string

This is probably because of the bitfields we have for the tx_offload field.
lib/mbuf/rte_mbuf_core.h:       RTE_MBUF_L2_LEN_BITS = 7,
lib/mbuf/rte_mbuf_core.h:       RTE_MBUF_L3_LEN_BITS = 9,
lib/mbuf/rte_mbuf_core.h:       RTE_MBUF_L4_LEN_BITS = 8,
lib/mbuf/rte_mbuf_core.h:       RTE_MBUF_OUTL3_LEN_BITS = 9,
lib/mbuf/rte_mbuf_core.h:       RTE_MBUF_OUTL2_LEN_BITS = 7,
lib/mbuf/rte_mbuf_core.h:                       uint64_t
l2_len:RTE_MBUF_L2_LEN_BITS;
lib/mbuf/rte_mbuf_core.h:                       uint64_t
l3_len:RTE_MBUF_L3_LEN_BITS;
lib/mbuf/rte_mbuf_core.h:                       uint64_t
l4_len:RTE_MBUF_L4_LEN_BITS;
lib/mbuf/rte_mbuf_core.h:                       uint64_t
outer_l3_len:RTE_MBUF_OUTL3_LEN_BITS;
lib/mbuf/rte_mbuf_core.h:                       uint64_t
outer_l2_len:RTE_MBUF_OUTL2_LEN_BITS;


Passing %PRIu64 instead of %u breaks build with gcc and clang.
../lib/mbuf/rte_mbuf.c: In function ‘rte_pktmbuf_dump’:
../lib/mbuf/rte_mbuf.c:760:36: error: format ‘%lu’ expects argument of
type ‘long unsigned int’, but argument 4 has type ‘int’
[-Werror=format=]
760 | fprintf(f, "%souter_l2_len=%"PRIu64, sep, m->outer_l2_len);
| ^~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~
| |
| int


I'll go with simple casting, like:
+            fprintf(f, "%souter_l2_len=%u", sep, (unsigned
int)m->outer_l2_len);


-- 
David Marchand