From dc7b48c404337891b5105df4d6751cf549a533eb Mon Sep 17 00:00:00 2001 From: Martin Schwenke Date: Tue, 15 Aug 2023 12:34:20 +1000 Subject: [PATCH] ctdb-common: Set immediate mode for pcap capture MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Fix a problem where ctdb_killtcp (almost always) fails to capture packets with --enable-pcap and libpcap ≥ 1.9.1. The problem is due to a gradual change in libpcap semantics when using pcap_get_selectable_fd(3PCAP) to get a file descriptor and then using that file descriptor in non-blocking mode. pcap_set_immediate_mode(3PCAP) says: pcap_set_immediate_mode() sets whether immediate mode should be set on a capture handle when the handle is activated. In immediate mode, packets are always delivered as soon as they arrive, with no buffering. and On Linux, with previous releases of libpcap, capture devices are always in immediate mode; however, in 1.5.0 and later, they are, by default, not in immediate mode, so if pcap_set_immediate_mode() is available, it should be used. However, it wasn't until libpcap commit 2ade7676101366983bd4f86bc039ffd25da8c126 (before libpcap 1.9.1) that it became a requirement to use pcap_set_immediate_mode(), even with a timeout of 0. More explanation in this libpcap issue comment: https://github.com/the-tcpdump-group/libpcap/issues/860#issuecomment-541204548 Do a configure check for pcap_set_immediate_mode() even though it has existed for 10 years. It is easy enough. BUG: https://bugzilla.samba.org/show_bug.cgi?id=15451 Signed-off-by: Martin Schwenke Reviewed-by: Amitay Isaacs Autobuild-User(master): Amitay Isaacs Autobuild-Date(master): Tue Aug 15 10:53:52 UTC 2023 on atb-devel-224 --- ctdb/common/system_socket.c | 7 +++++++ ctdb/wscript | 1 + 2 files changed, 8 insertions(+) diff --git a/ctdb/common/system_socket.c b/ctdb/common/system_socket.c index 16463af5a33..273b9c3400e 100644 --- a/ctdb/common/system_socket.c +++ b/ctdb/common/system_socket.c @@ -1007,6 +1007,13 @@ int ctdb_sys_open_capture_socket(const char *iface, void **private_data) DBG_ERR("Failed to set timeout for pcap capture\n"); goto fail; } +#ifdef HAVE_PCAP_SET_IMMEDIATE_MODE + ret = pcap_set_immediate_mode(pt, 1); + if (ret < 0) { + DBG_ERR("Failed to set immediate mode for pcap capture\n"); + goto fail; + } +#endif ret = pcap_activate(pt); if (ret < 0) { DBG_ERR("Failed to activate pcap capture\n"); diff --git a/ctdb/wscript b/ctdb/wscript index 88e42439f5a..a7b04541014 100644 --- a/ctdb/wscript +++ b/ctdb/wscript @@ -221,6 +221,7 @@ def configure(conf): if not conf.CHECK_FUNCS_IN('pcap_open_live', 'pcap', headers='pcap.h'): Logs.error('Need libpcap') sys.exit(1) + conf.CHECK_FUNCS_IN('pcap_set_immediate_mode', 'pcap', headers='pcap.h') if not conf.CHECK_FUNCS_IN('backtrace backtrace_symbols', 'execinfo', checklibc=True, headers='execinfo.h'):