Re: [PATCH] pcapng: allow any protocol link type for the interface block

[Stephen Hemminger <stephen@networkplumber.org>]

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Full list of types is here
https://www.tcpdump.org/linktypes.html

On Thu, May 29, 2025, 10:16 Schneide <schneide@qti.qualcomm.com> wrote:

> From: Dylan Schneider <schneide@qti.qualcomm.com>
>
> Allow the user to specify protocol link type when creating pcapng files.
> This change is needed to specify the protocol type in the pcapng file,
> DLT_EN10MB specifies ethernet packets only. This will allow dissectors
> for other protocols to be used on files generated by pcapng.
>
> Includes a breaking change to rte_pcapng_add_interface to add link_type
> parameter. Existing calls to the function have been updated to pass
> DLT_EN10MB for the link type argument.
>
> Fixes: d1da6d0d04c7 ("pcapng: require per-interface information")
> Signed-off-by: Dylan Schneider <schneide@qti.qualcomm.com>
> Cc: stephen@networkplumber.org
> ---
>
> diff --git a/.mailmap b/.mailmap
> index d9423aa..7ef0964 100644
> --- a/.mailmap
> +++ b/.mailmap
> @@ -388,6 +388,7 @@
>  Dumitru Ceara <dceara@redhat.com> <dumitru.ceara@gmail.com>
>  Duncan Bellamy <dunk@denkimushi.com>
>  Dustin Lundquist <dustin@null-ptr.net>
> +Dylan Schneider <schneide@qti.qualcomm.com>
>  Dzmitry Sautsa <dzmitryx.sautsa@intel.com>
>  Ed Czeck <ed.czeck@atomicrules.com>
>  Eduard Serra <eserra@vmware.com>
> diff --git a/app/dumpcap/main.c b/app/dumpcap/main.c
> index 3d3c0db..e0e2b26 100644
> --- a/app/dumpcap/main.c
> +++ b/app/dumpcap/main.c
> @@ -800,8 +800,8 @@ static dumpcap_out_t create_output(void)
>                 free(os);
>
>                 TAILQ_FOREACH(intf, &interfaces, next) {
> -                       if (rte_pcapng_add_interface(ret.pcapng,
> intf->port, intf->ifname,
> -                                                    intf->ifdescr,
> intf->opts.filter) < 0)
> +                       if (rte_pcapng_add_interface(ret.pcapng,
> intf->port, DLT_EN10MB,
> +                               intf->ifname, intf->ifdescr,
> intf->opts.filter) < 0)
>                                 rte_exit(EXIT_FAILURE,
> "rte_pcapng_add_interface %u failed\n",
>                                         intf->port);
>                 }
> diff --git a/app/test/test_pcapng.c b/app/test/test_pcapng.c
> index 8f2cff3..bcf9972 100644
> --- a/app/test/test_pcapng.c
> +++ b/app/test/test_pcapng.c
> @@ -345,7 +345,7 @@ test_add_interface(void)
>         }
>
>         /* Add interface to the file */
> -       ret = rte_pcapng_add_interface(pcapng, port_id,
> +       ret = rte_pcapng_add_interface(pcapng, port_id, DLT_EN10MB,
>                                        NULL, NULL, NULL);
>         if (ret < 0) {
>                 fprintf(stderr, "can not add port %u\n", port_id);
> @@ -353,7 +353,7 @@ test_add_interface(void)
>         }
>
>         /* Add interface with ifname and ifdescr */
> -       ret = rte_pcapng_add_interface(pcapng, port_id,
> +       ret = rte_pcapng_add_interface(pcapng, port_id, DLT_EN10MB,
>                                        "myeth", "Some long description",
> NULL);
>         if (ret < 0) {
>                 fprintf(stderr, "can not add port %u with ifname\n",
> port_id);
> @@ -361,7 +361,7 @@ test_add_interface(void)
>         }
>
>         /* Add interface with filter */
> -       ret = rte_pcapng_add_interface(pcapng, port_id,
> +       ret = rte_pcapng_add_interface(pcapng, port_id, DLT_EN10MB,
>                                        NULL, NULL, "tcp port 8080");
>         if (ret < 0) {
>                 fprintf(stderr, "can not add port %u with filter\n",
> port_id);
> @@ -406,7 +406,7 @@ test_write_packets(void)
>         }
>
>         /* Add interface to the file */
> -       ret = rte_pcapng_add_interface(pcapng, port_id,
> +       ret = rte_pcapng_add_interface(pcapng, port_id, DLT_EN10MB,
>                                        NULL, NULL, NULL);
>         if (ret < 0) {
>                 fprintf(stderr, "can not add port %u\n", port_id);
> diff --git a/lib/graph/graph_pcap.c b/lib/graph/graph_pcap.c
> index 89525f1..46fab8c 100644
> --- a/lib/graph/graph_pcap.c
> +++ b/lib/graph/graph_pcap.c
> @@ -117,7 +117,7 @@ graph_pcap_file_open(const char *filename)
>
>         /* Add the configured interfaces as possible capture ports */
>         RTE_ETH_FOREACH_DEV(portid) {
> -               ret = rte_pcapng_add_interface(pcapng_fd, portid,
> +               ret = rte_pcapng_add_interface(pcapng_fd, portid,
> DLT_EN10MB
>                                                NULL, NULL, NULL);
>                 if (ret < 0) {
>                         graph_err("Graph rte_pcapng_add_interface port %u
> failed: %d",
> diff --git a/lib/pcapng/rte_pcapng.c b/lib/pcapng/rte_pcapng.c
> index 16485b2..bed1e14 100644
> --- a/lib/pcapng/rte_pcapng.c
> +++ b/lib/pcapng/rte_pcapng.c
> @@ -205,7 +205,7 @@ pcapng_section_block(rte_pcapng_t *self,
>  /* Write an interface block for a DPDK port */
>  RTE_EXPORT_SYMBOL(rte_pcapng_add_interface)
>  int
> -rte_pcapng_add_interface(rte_pcapng_t *self, uint16_t port,
> +rte_pcapng_add_interface(rte_pcapng_t *self, uint16_t port, uint16_t
> link_type,
>                          const char *ifname, const char *ifdescr,
>                          const char *filter)
>  {
> @@ -277,7 +277,7 @@ rte_pcapng_add_interface(rte_pcapng_t *self, uint16_t
> port,
>         hdr = (struct pcapng_interface_block *)buf;
>         *hdr = (struct pcapng_interface_block) {
>                 .block_type = PCAPNG_INTERFACE_BLOCK,
> -               .link_type = 1,         /* DLT_EN10MB - Ethernet */
> +               .link_type = link_type,
>                 .block_length = len,
>         };
>
> diff --git a/lib/pcapng/rte_pcapng.h b/lib/pcapng/rte_pcapng.h
> index 48f2b57..0a35ec9 100644
> --- a/lib/pcapng/rte_pcapng.h
> +++ b/lib/pcapng/rte_pcapng.h
> @@ -71,6 +71,8 @@ rte_pcapng_close(rte_pcapng_t *self);
>   *  The handle to the packet capture file
>   * @param port
>   *  The Ethernet port to report stats on.
> + * @param link_type
> + *  The protocol link type of the packets
>   * @param ifname (optional)
>   *  Interface name to record in the file.
>   *  If not specified, name will be constructed from port
> @@ -84,7 +86,7 @@ rte_pcapng_close(rte_pcapng_t *self);
>   * must be added.
>   */
>  int
> -rte_pcapng_add_interface(rte_pcapng_t *self, uint16_t port,
> +rte_pcapng_add_interface(rte_pcapng_t *self, uint16_t port, uint16_t
> link_type,
>                          const char *ifname, const char *ifdescr,
>                          const char *filter);
>
>

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