core: rename/generalize UNIT(u)->test_start_limit() hook

Up until now the main reason why we didn't proceed with starting the
unit was exceed start limit burst. However, for unit types like mounts
the other reason could be effective ratelimit on /proc/self/mountinfo
event source. That means our mount unit state may not reflect current
kernel state. Hence, we need to attempt to re-run the start job again
after ratelimit on event source expires.

As we will be introducing another reason than start limit let's rename
the virtual function that implements the check.

src/core/automount.c

@@ -1063,7 +1063,7 @@ static bool automount_supported(void) {
         return supported;
 }
 
-static int automount_test_start_limit(Unit *u) {
+static int automount_can_start(Unit *u) {
         Automount *a = AUTOMOUNT(u);
         int r;
 
@@ -1075,7 +1075,7 @@ static int automount_test_start_limit(Unit *u) {
                 return r;
         }
 
-        return 0;
+        return 1;
 }
 
 static const char* const automount_result_table[_AUTOMOUNT_RESULT_MAX] = {
@@ -1142,5 +1142,5 @@ const UnitVTable automount_vtable = {
                 },
         },
 
-        .test_start_limit = automount_test_start_limit,
+        .can_start = automount_can_start,
 };

src/core/mount.c

@@ -2135,7 +2135,7 @@ static int mount_can_clean(Unit *u, ExecCleanMask *ret) {
         return exec_context_get_clean_mask(&m->exec_context, ret);
 }
 
-static int mount_test_start_limit(Unit *u) {
+static int mount_can_start(Unit *u) {
         Mount *m = MOUNT(u);
         int r;
 
@@ -2147,7 +2147,7 @@ static int mount_test_start_limit(Unit *u) {
                 return r;
         }
 
-        return 0;
+        return 1;
 }
 
 static const char* const mount_exec_command_table[_MOUNT_EXEC_COMMAND_MAX] = {
@@ -2248,5 +2248,5 @@ const UnitVTable mount_vtable = {
                 },
         },
 
-        .test_start_limit = mount_test_start_limit,
+        .can_start = mount_can_start,
 };

src/core/path.c

@@ -811,7 +811,7 @@ static void path_reset_failed(Unit *u) {
         p->result = PATH_SUCCESS;
 }
 
-static int path_test_start_limit(Unit *u) {
+static int path_can_start(Unit *u) {
         Path *p = PATH(u);
         int r;
 
@@ -823,7 +823,7 @@ static int path_test_start_limit(Unit *u) {
                 return r;
         }
 
-        return 0;
+        return 1;
 }
 
 static const char* const path_type_table[_PATH_TYPE_MAX] = {
@@ -882,5 +882,5 @@ const UnitVTable path_vtable = {
 
         .bus_set_property = bus_path_set_property,
 
-        .test_start_limit = path_test_start_limit,
+        .can_start = path_can_start,
 };

src/core/service.c

@@ -4482,7 +4482,7 @@ static const char *service_finished_job(Unit *u, JobType t, JobResult result) {
         return NULL;
 }
 
-static int service_test_start_limit(Unit *u) {
+static int service_can_start(Unit *u) {
         Service *s = SERVICE(u);
         int r;
 
@@ -4495,7 +4495,7 @@ static int service_test_start_limit(Unit *u) {
                 return r;
         }
 
-        return 0;
+        return 1;
 }
 
 static const char* const service_restart_table[_SERVICE_RESTART_MAX] = {
@@ -4669,5 +4669,5 @@ const UnitVTable service_vtable = {
                 .finished_job = service_finished_job,
         },
 
-        .test_start_limit = service_test_start_limit,
+        .can_start = service_can_start,
 };

src/core/socket.c

@@ -3427,7 +3427,7 @@ static int socket_can_clean(Unit *u, ExecCleanMask *ret) {
         return exec_context_get_clean_mask(&s->exec_context, ret);
 }
 
-static int socket_test_start_limit(Unit *u) {
+static int socket_can_start(Unit *u) {
         Socket *s = SOCKET(u);
         int r;
 
@@ -3439,7 +3439,7 @@ static int socket_test_start_limit(Unit *u) {
                 return r;
         }
 
-        return 0;
+        return 1;
 }
 
 static const char* const socket_exec_command_table[_SOCKET_EXEC_COMMAND_MAX] = {
@@ -3570,5 +3570,5 @@ const UnitVTable socket_vtable = {
                 },
         },
 
-        .test_start_limit = socket_test_start_limit,
+        .can_start = socket_can_start,
 };

src/core/swap.c

@@ -1581,7 +1581,7 @@ static int swap_can_clean(Unit *u, ExecCleanMask *ret) {
         return exec_context_get_clean_mask(&s->exec_context, ret);
 }
 
-static int swap_test_start_limit(Unit *u) {
+static int swap_can_start(Unit *u) {
         Swap *s = SWAP(u);
         int r;
 
@@ -1593,7 +1593,7 @@ static int swap_test_start_limit(Unit *u) {
                 return r;
         }
 
-        return 0;
+        return 1;
 }
 
 static const char* const swap_exec_command_table[_SWAP_EXEC_COMMAND_MAX] = {
@@ -1692,5 +1692,5 @@ const UnitVTable swap_vtable = {
                 },
         },
 
-        .test_start_limit = swap_test_start_limit,
+        .can_start = swap_can_start,
 };

src/core/timer.c

@@ -889,7 +889,7 @@ static int timer_can_clean(Unit *u, ExecCleanMask *ret) {
         return 0;
 }
 
-static int timer_test_start_limit(Unit *u) {
+static int timer_can_start(Unit *u) {
         Timer *t = TIMER(u);
         int r;
 
@@ -901,7 +901,7 @@ static int timer_test_start_limit(Unit *u) {
                 return r;
         }
 
-        return 0;
+        return 1;
 }
 
 static const char* const timer_base_table[_TIMER_BASE_MAX] = {
@@ -965,5 +965,5 @@ const UnitVTable timer_vtable = {
 
         .bus_set_property = bus_timer_set_property,
 
-        .test_start_limit = timer_test_start_limit,
+        .can_start = timer_can_start,
 };

src/core/unit.c

@@ -1904,9 +1904,9 @@ int unit_start(Unit *u) {
                 return unit_start(following);
         }
 
-        /* Check start rate limiting early so that failure conditions don't cause us to enter a busy loop. */
-        if (UNIT_VTABLE(u)->test_start_limit) {
-                r = UNIT_VTABLE(u)->test_start_limit(u);
+        /* Check our ability to start early so that failure conditions don't cause us to enter a busy loop. */
+        if (UNIT_VTABLE(u)->can_start) {
+                r = UNIT_VTABLE(u)->can_start(u);
                 if (r < 0)
                         return r;
         }

src/core/unit.h

@@ -665,7 +665,7 @@ typedef struct UnitVTable {
 
         /* If this function is set, it's invoked first as part of starting a unit to allow start rate
          * limiting checks to occur before we do anything else. */
-        int (*test_start_limit)(Unit *u);
+        int (*can_start)(Unit *u);
 
         /* The strings to print in status messages */
         UnitStatusMessageFormats status_message_formats;