service: pass service exit status to spawned On{Failure,Success}= dependency

When a service exits and triggers either an OnFailure= or OnSuccess=
dependency we now set a new environment variable for the ExecStart= and
ExecStartPre= process. This variable $MONITOR_METADATA exposes the
metadata relating to the service which triggered the dependency.
MONITOR_METADATA takes the following form:

MONITOR_METADATA="SERVICE_RESULT=<result-string0>,EXIT_CODE=<exit-code0>,EXIT_STATUS=<exit-status0>,INVOCATION_ID=<id>,UNIT=<triggering-unit0.service>;SERVICE_RESULT=<result-stringN>,EXIT_CODE=<exit-codeN>,=EXIT_STATUS=<exit-statusN>,INVOCATION_ID=<id>,UNIT=<triggering-unitN.service>"

MONITOR_METADATA is space separated set of metadata relating to the
service(s) which triggered the dependency. This is a list since if we
have 2 services which trigger the same dependency then the dependency
start job may be merged. In this case we need to pass both service
metadata to the triggered service. If there is no job merging then
MONITOR_METADATA will be a single entry.

For example, in the case we had a service "failer.service" which
triggers "failer-handler.service", the following variable is exported to
the ExecStart= and ExecStartPre= processes in failer-handler.service:

MONITOR_METADATA="SERVICE_RESULT=exit-code,EXIT_CODE=exited,EXIT_STATUS=1,INVOCATION_ID=67c657ed7b34466ea369abdf994c6393,UNIT=failer.service"

In another example where we have failer.service and failer2.service
which both also trigger failer-handler.service then the start job for
failer-handler.service may be merged and we might get the following:

MONITOR_METADATA="SERVICE_RESULT=exit-code,EXIT_CODE=exited,EXIT_STATUS=1,INVOCATION_ID=16a93ad196c94109990fb8b9aa5eef5f,UNIT=failer.service;SERVICE_RESULT=exit-code,EXIT_CODE=exited,EXIT_STATUS=1,INVOCATION_ID=ff70131e4cc145e994fb621de25a3e8f,UNIT=failer2.service"

1 files changed, 14 insertions, 13 deletions

diff --git a/src/core/execute.h b/src/core/execute.h
index b0da375def..805e9b4765 100644
--- a/src/core/execute.h
+++ b/src/core/execute.h
@@ -370,21 +370,22 @@ static inline bool exec_context_with_rootfs(const ExecContext *c) {
 }
 
 typedef enum ExecFlags {
-        EXEC_APPLY_SANDBOXING  = 1 << 0,
-        EXEC_APPLY_CHROOT      = 1 << 1,
-        EXEC_APPLY_TTY_STDIN   = 1 << 2,
-        EXEC_PASS_LOG_UNIT     = 1 << 3, /* Whether to pass the unit name to the service's journal stream connection */
-        EXEC_CHOWN_DIRECTORIES = 1 << 4, /* chown() the runtime/state/cache/log directories to the user we run as, under all conditions */
-        EXEC_NSS_BYPASS_BUS    = 1 << 5, /* Set the SYSTEMD_NSS_BYPASS_BUS environment variable, to disable nss-systemd for dbus */
-        EXEC_CGROUP_DELEGATE   = 1 << 6,
-        EXEC_IS_CONTROL        = 1 << 7,
-        EXEC_CONTROL_CGROUP    = 1 << 8, /* Place the process not in the indicated cgroup but in a subcgroup '/.control', but only EXEC_CGROUP_DELEGATE and EXEC_IS_CONTROL is set, too */
-        EXEC_WRITE_CREDENTIALS = 1 << 9, /* Set up the credential store logic */
+        EXEC_APPLY_SANDBOXING      = 1 << 0,
+        EXEC_APPLY_CHROOT          = 1 << 1,
+        EXEC_APPLY_TTY_STDIN       = 1 << 2,
+        EXEC_PASS_LOG_UNIT         = 1 << 3, /* Whether to pass the unit name to the service's journal stream connection */
+        EXEC_CHOWN_DIRECTORIES     = 1 << 4, /* chown() the runtime/state/cache/log directories to the user we run as, under all conditions */
+        EXEC_NSS_BYPASS_BUS        = 1 << 5, /* Set the SYSTEMD_NSS_BYPASS_BUS environment variable, to disable nss-systemd for dbus */
+        EXEC_CGROUP_DELEGATE       = 1 << 6,
+        EXEC_IS_CONTROL            = 1 << 7,
+        EXEC_CONTROL_CGROUP        = 1 << 8, /* Place the process not in the indicated cgroup but in a subcgroup '/.control', but only EXEC_CGROUP_DELEGATE and EXEC_IS_CONTROL is set, too */
+        EXEC_WRITE_CREDENTIALS     = 1 << 9, /* Set up the credential store logic */
 
         /* The following are not used by execute.c, but by consumers internally */
-        EXEC_PASS_FDS          = 1 << 10,
-        EXEC_SETENV_RESULT     = 1 << 11,
-        EXEC_SET_WATCHDOG      = 1 << 12,
+        EXEC_PASS_FDS              = 1 << 10,
+        EXEC_SETENV_RESULT         = 1 << 11,
+        EXEC_SET_WATCHDOG          = 1 << 12,
+        EXEC_SETENV_MONITOR_RESULT = 1 << 13, /* Pass exit status to OnFailure= and OnSuccess= dependencies. */
 } ExecFlags;
 
 /* Parameters for a specific invocation of a command. This structure is put together right before a command is