From 44c662ce66854aff8adbe0142da800812f952f36 Mon Sep 17 00:00:00 2001 From: Guy Harris Date: Sat, 5 Jan 2019 19:06:10 -0800 Subject: [PATCH] Replace ancient notes about modifying libpcap with a link to a newer doc. Instead of giving horribly out-of-date instructions on how to add a new module to libpcap, just point to the document that I started whipping up earlier today (it definitely needs work - it's incomplete - but I'll be getting back to it). While we're at it, update the notes on adding support for new LINKTYPE_ values to libwiretap, and note that it's only necessary if you had to add a new DLT_ *and* there isn't already a WTAP_ENCAP_ value that would correspond to that DLT_. Change-Id: I3882d0a57b29e98f73c074317bc6df7458fcc677 Reviewed-on: https://code.wireshark.org/review/31397 Petri-Dish: Guy Harris Tested-by: Petri Dish Buildbot Reviewed-by: Guy Harris --- .../wsdg_src/WSDG_chapter_capture.asciidoc | 68 +++++-------------- 1 file changed, 18 insertions(+), 50 deletions(-) diff --git a/docbook/wsdg_src/WSDG_chapter_capture.asciidoc b/docbook/wsdg_src/WSDG_chapter_capture.asciidoc index 4e6c55a36b..db6505fe8d 100644 --- a/docbook/wsdg_src/WSDG_chapter_capture.asciidoc +++ b/docbook/wsdg_src/WSDG_chapter_capture.asciidoc @@ -16,60 +16,28 @@ This chapter needs to be reviewed and extended. === How To Add A New Capture Type To Libpcap -The following is an updated excerpt from a developer mailing list mail about -adding ISO 9141 and 14230 (simple serial line card diagnostics) to Wireshark: +For this discussion, I'll assume you're working with libpcap 1.0 or +later. You probably don't want to work with a version older than 1.0, +even if whatever OS you're using happens to include libpcap - older +versions are not as friendly towards adding support for devices other +than standard network interfaces. -For libpcap, the first thing you’d need to do would be to get `{dlt-glob}` values -for all the link-layer protocols you’d need. If ISO 9141 and 14230 use the same -link-layer protocol, they might be able to share a `{dlt-glob}` value, unless the -only way to know what protocols are running above the link layer is to know -which link-layer protocol is being used, in which case you might want separate -`{dlt-glob}` values. +First, read -For the rest of the libpcap discussion, I'll assume you're working with libpcap -1.0 or later and that this is on a UN*X platform. You probably don't want to -work with a version older than 1.0, even if whatever OS you're using happens to -include libpcap - older versions are not as friendly towards adding support for -devices other than standard network interfaces. +link:https://github.com/the-tcpdump-group/libpcap/blob/master/doc/README.capture-module:[the +libpcap documentation on writing a new libpcap module] -Then you’d probably add to the `pcap_open_live()` routine, for whatever -platform or platforms this code should work, something such as a check -for device names that look like serial port names and, if the check -succeeds, a call to a routine to open the serial port. +(It's currently incomplete, but I'll be finishing it up over time. If +you have contributions, feel free to submit pull requests for it.) -See, for example, the `#ifdef HAVE_DAG_API` code in _pcap-linux.c_ and -_pcap-bpf.c_. - -The serial port open routine would open the serial port device, set the baud -rate and do anything else needed to open the device. It’d allocate a `pcap_t`, -set its `fd` member to the file descriptor for the serial device, set the -`snapshot` member to the argument passed to the open routine, set the `linktype` -member to one of the `{dlt-glob}` values, and set the `selectable_fd` member to -the same value as the `fd` member. It should also set the `dlt_count` member to -the number of `{dlt-glob}` values to support, and allocate an array of -`dlt_count` `u_int`s, assign it to the `dlt_list` member, and fill in that list -with all the `{dlt-glob}` values. - -You’d then set the various `_*_op` fields to routines to handle the operations in -question. `read_op` is the routine that’d read packets from the device. `inject_op` -would be for sending packets; if you don't care about that, you’d set it to a -routine that returns an error indication. `setfilter_op` can probably just be set -to `install_bpf_program`. `set_datalink` would just set the `linktype` member to the -specified value if it’s one of the values for OBD, otherwise it should return an -error. `getnonblock_op` can probably be set to `pcap_getnonblock_fd`. `setnonblock_op` -can probably be set to `pcap_setnonblock_fd`. `stats_op` would be set to a routine -that reports statistics. `close_op` can probably be set to `pcap_close_common`. - -If there’s more than one `{dlt-glob}` value, you definitely want a `set_datalink` -routine so that the user can select the appropriate link-layer type. - -For Wireshark, you’d add support for those `{dlt-glob}` values to -_wiretap/libpcap.c_, which might mean adding one or more _WTAP_ENCAP_ types to -_wtap.h_ and to the `encap_table[]` table in _wiretap/wtap.c_. You’d then -have to write a dissector or dissectors for the link-layer protocols or -protocols and have them register themselves with the `wtap_encap` dissector -table, with the appropriate _WTAP_ENCAP_ values by calling -`dissector_add_uint()`. +If you had to introduce one or more new `{dlt-glob}` values, you will +also have to add support in Wireshark for those `{dlt-glob}` values to +_wiretap/pcap-common.c_, which might mean adding one or more +_WTAP_ENCAP_ types to _wtap.h_ and to the `encap_table[]` table in +_wiretap/wtap.c_. You’d thehave to write a dissector or dissectors for +the link-layer protocols or protocols and have them register themselves +with the `wtap_encap` dissector table, with the appropriate _WTAP_ENCAP_ +values by calling `dissector_add_uint()`. [[ChCaptureExtcap]]