core: treat JobTimeout=0 as equivalent to JobTimeout=infinity

Corrects an incompatibility introduced with 36c16a7cdd.

Fixes: #2537

src/core/load-fragment-gperf.gperf.m4

@@ -161,7 +161,7 @@ Unit.OnFailureJobMode,           config_parse_job_mode,              0,
 Unit.OnFailureIsolate,           config_parse_job_mode_isolate,      0,                             offsetof(Unit, on_failure_job_mode)
 Unit.IgnoreOnIsolate,            config_parse_bool,                  0,                             offsetof(Unit, ignore_on_isolate)
 Unit.IgnoreOnSnapshot,           config_parse_warn_compat,           DISABLED_LEGACY,               0
-Unit.JobTimeoutSec,              config_parse_sec,                   0,                             offsetof(Unit, job_timeout)
+Unit.JobTimeoutSec,              config_parse_sec_fix_0,             0,                             offsetof(Unit, job_timeout)
 Unit.JobTimeoutAction,           config_parse_failure_action,        0,                             offsetof(Unit, job_timeout_action)
 Unit.JobTimeoutRebootArgument,   config_parse_string,                0,                             offsetof(Unit, job_timeout_reboot_arg)
 Unit.StartLimitInterval,         config_parse_sec,                   0,                             offsetof(Unit, start_limit.interval)

src/core/load-fragment.c

@@ -1757,6 +1757,42 @@ int config_parse_service_timeout(
         return 0;
 }
 
+int config_parse_sec_fix_0(
+                const char *unit,
+                const char *filename,
+                unsigned line,
+                const char *section,
+                unsigned section_line,
+                const char *lvalue,
+                int ltype,
+                const char *rvalue,
+                void *data,
+                void *userdata) {
+
+        usec_t *usec = data;
+        int r;
+
+        assert(filename);
+        assert(lvalue);
+        assert(rvalue);
+        assert(usec);
+
+        /* This is pretty much like config_parse_sec(), except that this treats a time of 0 as infinity, for
+         * compatibility with older versions of systemd where 0 instead of infinity was used as indicator to turn off a
+         * timeout. */
+
+        r = parse_sec(rvalue, usec);
+        if (r < 0) {
+                log_syntax(unit, LOG_ERR, filename, line, r, "Failed to parse %s= parameter, ignoring: %s", lvalue, rvalue);
+                return 0;
+        }
+
+        if (*usec <= 0)
+                *usec = USEC_INFINITY;
+
+        return 0;
+}
+
 int config_parse_busname_service(
                 const char *unit,
                 const char *filename,

src/core/load-fragment.h

@@ -109,6 +109,7 @@ int config_parse_bus_name(const char* unit, const char *filename, unsigned line,
 int config_parse_exec_utmp_mode(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 int config_parse_working_directory(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 int config_parse_fdname(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
+int config_parse_sec_fix_0(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 
 /* gperf prototypes */
 const struct ConfigPerfItem* load_fragment_gperf_lookup(const char *key, unsigned length);