From 624161cd2e922e790a2aa855c595b9074dc766c2 Mon Sep 17 00:00:00 2001 From: Andrew Geissler Date: Tue, 9 Apr 2019 16:01:01 -0500 Subject: Handle mapper introspect race condition There is a pervasive issue within OpenBMC where a dbus service may be started and on the bus, but before mapper can introspect it, a dependent service queries mapper for that objects information. In most situations a service writer can avoid this by using the Wants=mapper-wait@-xyz* syntax. This does not work however if two or more dbus services implement the same dbus object path. The host_check_main application is one service that is hitting this issue. It requires the /xyz/openbmc_project/control/host0 object path which is implemented by two dbus services. The solution here is to first try mapper, but if that fails to use a hard coded dbus service name. The value of mapper for this type of function is up for debate within the community but for now, get a compromise in that first tries mapper, and if not available tries the hard coded well-known service name. Tested: Verified the following within QEMU: - Good path works as expected, mapper response used - GetObject fails for mapper call, successfully used hard coded path - Service not available on dbus, verified exception reported Change-Id: I14dfaf2ce43392a19a2a5a3131534f55c6eb6f4a Signed-off-by: Andrew Geissler --- host_check_main.cpp | 22 +++++++++++++--------- 1 file changed, 13 insertions(+), 9 deletions(-) diff --git a/host_check_main.cpp b/host_check_main.cpp index 311e6e2..182c501 100644 --- a/host_check_main.cpp +++ b/host_check_main.cpp @@ -18,6 +18,7 @@ using sdbusplus::exception::SdBusError; constexpr auto MAPPER_BUSNAME = "xyz.openbmc_project.ObjectMapper"; constexpr auto MAPPER_PATH = "/xyz/openbmc_project/object_mapper"; constexpr auto MAPPER_INTERFACE = "xyz.openbmc_project.ObjectMapper"; +constexpr auto CONTROL_HOST_DEFAULT_SVC = "xyz.openbmc_project.Control.Host"; constexpr auto CONTROL_HOST_PATH = "/xyz/openbmc_project/control/host0"; constexpr auto CONTROL_HOST_INTERFACE = "xyz.openbmc_project.Control.Host"; @@ -71,19 +72,22 @@ void sendHeartbeat(sdbusplus::bus::bus& bus) } catch (const SdBusError& e) { - log("Error in mapper call for control host", - entry("ERROR=%s", e.what())); - throw; + log("Error in mapper call for control host, use default " + "service", + entry("ERROR=%s", e.what())); } - if (mapperResponse.empty()) + std::string host; + if (!mapperResponse.empty()) { - log("Error reading mapper resp for control host"); - // TODO openbmc/openbmc#851 - Once available, throw returned error - throw std::runtime_error("Error reading mapper resp for control host"); + log("Use mapper response"); + host = mapperResponse.begin()->first; + } + else + { + log("Use hard coded host"); + host = CONTROL_HOST_DEFAULT_SVC; } - - const auto& host = mapperResponse.begin()->first; auto method = bus.new_method_call(host.c_str(), CONTROL_HOST_PATH, CONTROL_HOST_INTERFACE, "Execute"); -- cgit v1.2.3