[ovs-dev] [PATCH] dpdk: Deprecate pdump support.

[Ilya Maximets]

The conventional way for packet dumping in OVS is to use ovs-tcpdump
that works via traffic mirroring.  DPDK pdump could probably be used
for some lower level debugging, but it is not commonly used for
various reasons.

There are lots of limitations for using this functionality in practice.
Most of them connected with running secondary pdump process and
memory layout issues like requirement to disable ASLR in kernel.
More details are available in DPDK guide:
https://doc.dpdk.org/guides/prog_guide/multi_proc_support.html#multi-process-limitations

Beside the functional limitations it's also hard to use this
functionality correctly.  User must be sure that OVS and pdump utility
are running on different CPU cores, which is hard because non-PMD
threads could float over available CPU cores.  This or any other
misconfiguration will likely lead to crash of the pdump utility
or/and OVS.

Another problem is that the user must actually have this special pdump
utility in a system and it might be not available in distributions.

This change disables pdump support by default introducing special
configuration option '--enable-dpdk-pdump'.  Deprecation warnings will
be shown to users on configuration and in runtime.

Claiming to completely remove this functionality from OVS in one
of the next releases.

Signed-off-by: Ilya Maximets <i.maximets at ovn.org>
Acked-by: Aaron Conole <aconole at redhat.com>
---

Version 1:
  * No changes since RFC.
  * Added ACK from Aaron.

 .travis/linux-build.sh              |  4 +++-
 Documentation/topics/dpdk/pdump.rst |  8 +++++++-
 NEWS                                |  4 ++++
 acinclude.m4                        | 24 ++++++++++++++++++------
 lib/dpdk.c                          |  2 ++
 5 files changed, 34 insertions(+), 8 deletions(-)

diff --git a/.travis/linux-build.sh b/.travis/linux-build.sh
index 69260181b..4e74973a3 100755
--- a/.travis/linux-build.sh
+++ b/.travis/linux-build.sh
@@ -124,7 +124,7 @@ function install_dpdk()
     sed -i '/CONFIG_RTE_EAL_IGB_UIO=y/s/=y/=n/' build/.config
     sed -i '/CONFIG_RTE_KNI_KMOD=y/s/=y/=n/' build/.config
 
-    # Enable pdump.  This will enable building of the relevant OVS code.
+    # Enable pdump support in DPDK.
     sed -i '/CONFIG_RTE_LIBRTE_PMD_PCAP=n/s/=n/=y/' build/.config
     sed -i '/CONFIG_RTE_LIBRTE_PDUMP=n/s/=n/=y/' build/.config
 
@@ -168,6 +168,8 @@ if [ "$DPDK" ] || [ "$DPDK_SHARED" ]; then
         DPDK_VER="18.11.2"
     fi
     install_dpdk $DPDK_VER
+    # Enable pdump support in OVS.
+    EXTRA_OPTS="${EXTRA_OPTS} --enable-dpdk-pdump"
     if [ "$CC" = "clang" ]; then
         # Disregard cast alignment errors until DPDK is fixed
         CFLAGS_FOR_OVS="${CFLAGS_FOR_OVS} -Wno-cast-align"
diff --git a/Documentation/topics/dpdk/pdump.rst b/Documentation/topics/dpdk/pdump.rst
index 7bd1d3e9f..b4d8aa8e9 100644
--- a/Documentation/topics/dpdk/pdump.rst
+++ b/Documentation/topics/dpdk/pdump.rst
@@ -27,10 +27,16 @@ pdump
 
 .. versionadded:: 2.6.0
 
+.. warning::
+
+   DPDK pdump support is deprecated in OVS and will be removed in next
+   releases.
+
 pdump allows you to listen on DPDK ports and view the traffic that is passing
 on them. To use this utility, one must have libpcap installed on the system.
 Furthermore, DPDK must be built with ``CONFIG_RTE_LIBRTE_PDUMP=y`` and
-``CONFIG_RTE_LIBRTE_PMD_PCAP=y``.
+``CONFIG_RTE_LIBRTE_PMD_PCAP=y``. OVS should be built with
+``--enable-dpdk-pdump`` configuration option.
 
 .. warning::
 
diff --git a/NEWS b/NEWS
index 88b818948..0d65d5a7f 100644
--- a/NEWS
+++ b/NEWS
@@ -10,6 +10,10 @@ Post-v2.12.0
        if supported by libbpf.
      * Add option to enable, disable and query TCP sequence checking in
        conntrack.
+   - DPDK:
+     * DPDK pdump packet capture support disabled by default. New configure
+       option '--enable-dpdk-pdump' to enable it.
+     * DPDK pdump support is deprecated and will be removed in next releases.
 
 v2.12.0 - 03 Sep 2019
 ---------------------
diff --git a/acinclude.m4 b/acinclude.m4
index fc6157ac8..542637ac8 100644
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -357,12 +357,24 @@ AC_DEFUN([OVS_CHECK_DPDK], [
       AC_DEFINE([VHOST_NUMA], [1], [NUMA Aware vHost support detected in DPDK.])
     ], [], [[#include <rte_config.h>]])
 
-    AC_CHECK_DECL([RTE_LIBRTE_PMD_PCAP], [
-      OVS_FIND_DEPENDENCY([pcap_dump], [pcap], [libpcap])
-      AC_CHECK_DECL([RTE_LIBRTE_PDUMP], [
-        AC_DEFINE([DPDK_PDUMP], [1], [DPDK pdump enabled in OVS.])
-      ], [], [[#include <rte_config.h>]])
-    ], [], [[#include <rte_config.h>]])
+   AC_MSG_CHECKING([whether DPDK pdump support is enabled])
+   AC_ARG_ENABLE(
+     [dpdk-pdump],
+     [AC_HELP_STRING([--enable-dpdk-pdump],
+                     [Enable DPDK pdump packet capture support])],
+     [AC_MSG_RESULT([yes])
+      AC_MSG_WARN([DPDK pdump is deprecated, consider using ovs-tcpdump instead])
+      AC_CHECK_DECL([RTE_LIBRTE_PMD_PCAP], [
+        OVS_FIND_DEPENDENCY([pcap_dump], [pcap], [libpcap])
+        AC_CHECK_DECL([RTE_LIBRTE_PDUMP], [
+          AC_DEFINE([DPDK_PDUMP], [1], [DPDK pdump enabled in OVS.])
+        ], [
+          AC_MSG_ERROR([RTE_LIBRTE_PDUMP is not defined in rte_config.h])
+        ], [[#include <rte_config.h>]])
+      ], [
+        AC_MSG_ERROR([RTE_LIBRTE_PMD_PCAP is not defined in rte_config.h])
+      ], [[#include <rte_config.h>]])],
+      [AC_MSG_RESULT([no])])
 
     AC_CHECK_DECL([RTE_LIBRTE_MLX5_PMD], [dnl found
       OVS_FIND_DEPENDENCY([mnl_attr_put], [mnl], [libmnl])
diff --git a/lib/dpdk.c b/lib/dpdk.c
index f90cda75a..21dd47e80 100644
--- a/lib/dpdk.c
+++ b/lib/dpdk.c
@@ -434,6 +434,8 @@ dpdk_init__(const struct smap *ovs_other_config)
 
 #ifdef DPDK_PDUMP
     VLOG_INFO("DPDK pdump packet capture enabled");
+    VLOG_WARN("DPDK pdump support is deprecated and "
+              "will be removed in next OVS releases.");
     err = rte_pdump_init(ovs_rundir());
     if (err) {
         VLOG_INFO("Error initialising DPDK pdump");
-- 
2.17.1