unit: handle nicely of certain unit types are not supported on specific systems

Containers do not really support .device, .automount or .swap units;
Systems compiled without support for swap do not support .swap units;
Systems without kdbus do not support .busname units.

With this change attempts to start a unsupported unit types will result
in an immediate "unsupported" job result, which is a lot more
descriptive then before. Also, attempts to start device units in
containers will now immediately fail instead of causing jobs to be
enqueued that never go away.

src/core/automount.c

@@ -807,6 +807,17 @@ static void automount_reset_failed(Unit *u) {
         a->result = AUTOMOUNT_SUCCESS;
 }
 
+static bool automount_supported(Manager *m) {
+        static int supported = -1;
+
+        assert(m);
+
+        if (supported < 0)
+                supported = access("/dev/autofs", F_OK) >= 0;
+
+        return supported;
+}
+
 static const char* const automount_state_table[_AUTOMOUNT_STATE_MAX] = {
         [AUTOMOUNT_DEAD] = "dead",
         [AUTOMOUNT_WAITING] = "waiting",
@@ -859,6 +870,7 @@ const UnitVTable automount_vtable = {
         .bus_vtable = bus_automount_vtable,
 
         .shutdown = automount_shutdown,
+        .supported = automount_supported,
 
         .status_message_formats = {
                 .finished_start_job = {

src/core/busname.c

@@ -971,6 +971,16 @@ static int busname_get_timeout(Unit *u, uint64_t *timeout) {
         return 1;
 }
 
+static bool busname_supported(Manager *m) {
+        int supported = -1;
+        assert(m);
+
+        if (supported < 0)
+                supported = access("/sys/fs/kdbus", F_OK) >= 0;
+
+        return supported;
+}
+
 static const char* const busname_state_table[_BUSNAME_STATE_MAX] = {
         [BUSNAME_DEAD] = "dead",
         [BUSNAME_MAKING] = "making",
@@ -1032,6 +1042,8 @@ const UnitVTable busname_vtable = {
 
         .reset_failed = busname_reset_failed,
 
+        .supported = busname_supported,
+
         .bus_interface = "org.freedesktop.systemd1.BusName",
         .bus_vtable = bus_busname_vtable,
 

src/core/device.c

@@ -673,6 +673,19 @@ static int device_dispatch_io(sd_event_source *source, int fd, uint32_t revents,
         return 0;
 }
 
+static bool device_supported(Manager *m) {
+        static int read_only = -1;
+        assert(m);
+
+        /* If /sys is read-only we don't support device units, and any
+         * attempts to start one should fail immediately. */
+
+        if (read_only < 0)
+                read_only = path_is_read_only_fs("/sys");
+
+        return read_only <= 0;
+}
+
 static const char* const device_state_table[_DEVICE_STATE_MAX] = {
         [DEVICE_DEAD] = "dead",
         [DEVICE_PLUGGED] = "plugged"
@@ -708,6 +721,7 @@ const UnitVTable device_vtable = {
 
         .enumerate = device_enumerate,
         .shutdown = device_shutdown,
+        .supported = device_supported,
 
         .status_message_formats = {
                 .starting_stopping = {

src/core/job.c

@@ -547,6 +547,8 @@ int job_run_and_invalidate(Job *j) {
                         r = job_finish_and_invalidate(j, JOB_INVALID, true);
                 else if (r == -EPROTO)
                         r = job_finish_and_invalidate(j, JOB_ASSERT, true);
+                else if (r == -ENOTSUP)
+                        r = job_finish_and_invalidate(j, JOB_UNSUPPORTED, true);
                 else if (r == -EAGAIN) {
                         j->state = JOB_WAITING;
                         m->n_running_jobs--;
@@ -591,12 +593,16 @@ _pure_ static const char *job_get_status_message_format_try_harder(Unit *u, JobT
         if (t == JOB_START) {
                 if (result == JOB_DONE)
                         return "Started %s.";
+                else if (result == JOB_TIMEOUT)
+                        return "Timed out starting %s.";
                 else if (result == JOB_FAILED)
                         return "Failed to start %s.";
                 else if (result == JOB_DEPENDENCY)
                         return "Dependency failed for %s.";
-                else if (result == JOB_TIMEOUT)
+                else if (result == JOB_ASSERT)
-                        return "Timed out starting %s.";
+                        return "Assertion failed for %s.";
+                else if (result == JOB_UNSUPPORTED)
+                        return "Starting of %s not supported.";
         } else if (t == JOB_STOP || t == JOB_RESTART) {
                 if (result == JOB_DONE)
                         return "Stopped %s.";
@@ -637,6 +643,11 @@ static void job_print_status_message(Unit *u, JobType t, JobResult result) {
                                 unit_status_printf(u, ANSI_GREEN_ON "  OK  " ANSI_HIGHLIGHT_OFF, format);
                         break;
 
+                case JOB_TIMEOUT:
+                        manager_flip_auto_status(u->manager, true);
+                        unit_status_printf(u, ANSI_HIGHLIGHT_RED_ON " TIME " ANSI_HIGHLIGHT_OFF, format);
+                        break;
+
                 case JOB_FAILED: {
                         bool quotes;
 
@@ -655,16 +666,16 @@ static void job_print_status_message(Unit *u, JobType t, JobResult result) {
                         unit_status_printf(u, ANSI_HIGHLIGHT_YELLOW_ON "DEPEND" ANSI_HIGHLIGHT_OFF, format);
                         break;
 
-                case JOB_TIMEOUT:
-                        manager_flip_auto_status(u->manager, true);
-                        unit_status_printf(u, ANSI_HIGHLIGHT_RED_ON " TIME " ANSI_HIGHLIGHT_OFF, format);
-                        break;
-
                 case JOB_ASSERT:
                         manager_flip_auto_status(u->manager, true);
                         unit_status_printf(u, ANSI_HIGHLIGHT_YELLOW_ON "ASSERT" ANSI_HIGHLIGHT_OFF, format);
                         break;
 
+                case JOB_UNSUPPORTED:
+                        manager_flip_auto_status(u->manager, true);
+                        unit_status_printf(u, ANSI_HIGHLIGHT_YELLOW_ON "UNSUPP" ANSI_HIGHLIGHT_OFF, format);
+                        break;
+
                 default:
                         ;
                 }
@@ -1200,6 +1211,7 @@ static const char* const job_result_table[_JOB_RESULT_MAX] = {
         [JOB_SKIPPED] = "skipped",
         [JOB_INVALID] = "invalid",
         [JOB_ASSERT] = "assert",
+        [JOB_UNSUPPORTED] = "unsupported",
 };
 
 DEFINE_STRING_TABLE_LOOKUP(job_result, JobResult);

src/core/job.h

@@ -96,12 +96,13 @@ enum JobMode {
 enum JobResult {
         JOB_DONE,                /* Job completed successfully */
         JOB_CANCELED,            /* Job canceled by a conflicting job installation or by explicit cancel request */
-        JOB_TIMEOUT,             /* JobTimeout elapsed */
+        JOB_TIMEOUT,             /* Job timeout elapsed */
         JOB_FAILED,              /* Job failed */
         JOB_DEPENDENCY,          /* A required dependency job did not result in JOB_DONE */
         JOB_SKIPPED,             /* Negative result of JOB_VERIFY_ACTIVE */
         JOB_INVALID,             /* JOB_RELOAD of inactive unit */
         JOB_ASSERT,              /* Couldn't start a unit, because an assert didn't hold */
+        JOB_UNSUPPORTED,         /* Couldn't start a unit, because the unit type is not supported on the system */
         _JOB_RESULT_MAX,
         _JOB_RESULT_INVALID = -1
 };

src/core/manager.c

@@ -946,15 +946,24 @@ Manager* manager_free(Manager *m) {
 }
 
 int manager_enumerate(Manager *m) {
-        int r = 0, q;
+        int r = 0;
         UnitType c;
 
         assert(m);
 
         /* Let's ask every type to load all units from disk/kernel
          * that it might know */
-        for (c = 0; c < _UNIT_TYPE_MAX; c++)
+        for (c = 0; c < _UNIT_TYPE_MAX; c++) {
-                if (unit_vtable[c]->enumerate) {
+                int q;
+
+                if (unit_vtable[c]->supported && !unit_vtable[c]->supported(m)) {
+                        log_info("Unit type .%s is not supported on this system.", unit_type_to_string(c));
+                        continue;
+                }
+
+                if (!unit_vtable[c]->enumerate)
+                        continue;
+
                 q = unit_vtable[c]->enumerate(m);
                 if (q < 0)
                         r = q;

src/core/mount.c

@@ -1447,7 +1447,6 @@ static int mount_add_one(
                         goto fail;
                 }
 
-
                 if (m->running_as == SYSTEMD_SYSTEM) {
                         const char* target;
 

src/core/swap.c

@@ -1453,6 +1453,21 @@ static int swap_get_timeout(Unit *u, uint64_t *timeout) {
         return 1;
 }
 
+static bool swap_supported(Manager *m) {
+        static int supported = -1;
+
+        /* If swap support is not available in the kernel, or we are
+         * running in a container we don't support swap units, and any
+         * attempts to starting one should fail immediately. */
+
+        if (supported < 0)
+                supported =
+                        access("/proc/swaps", F_OK) >= 0 &&
+                        detect_container(NULL) <= 0;
+
+        return supported;
+}
+
 static const char* const swap_state_table[_SWAP_STATE_MAX] = {
         [SWAP_DEAD] = "dead",
         [SWAP_ACTIVATING] = "activating",
@@ -1539,6 +1554,7 @@ const UnitVTable swap_vtable = {
 
         .enumerate = swap_enumerate,
         .shutdown = swap_shutdown,
+        .supported = swap_supported,
 
         .status_message_formats = {
                 .starting_stopping = {

src/core/unit.c

@@ -1453,6 +1453,9 @@ int unit_start(Unit *u) {
         unit_status_log_starting_stopping_reloading(u, JOB_START);
         unit_status_print_starting_stopping(u, JOB_START);
 
+        if (UNIT_VTABLE(u)->supported && !UNIT_VTABLE(u)->supported(u->manager))
+                return -ENOTSUP;
+
         /* If it is stopped, but we cannot start it, then fail */
         if (!UNIT_VTABLE(u)->start)
                 return -EBADR;
@@ -1496,9 +1499,9 @@ int unit_stop(Unit *u) {
         if (UNIT_IS_INACTIVE_OR_FAILED(state))
                 return -EALREADY;
 
-        if ((following = unit_following(u))) {
+        following = unit_following(u);
-                log_unit_debug(u->id, "Redirecting stop request from %s to %s.",
+        if (following) {
-                               u->id, following->id);
+                log_unit_debug(u->id, "Redirecting stop request from %s to %s.", u->id, following->id);
                 return unit_stop(following);
         }
 
@@ -1535,15 +1538,13 @@ int unit_reload(Unit *u) {
                 return -EALREADY;
 
         if (state != UNIT_ACTIVE) {
-                log_unit_warning(u->id, "Unit %s cannot be reloaded because it is inactive.",
+                log_unit_warning(u->id, "Unit %s cannot be reloaded because it is inactive.", u->id);
-                                 u->id);
                 return -ENOEXEC;
         }
 
         following = unit_following(u);
         if (following) {
-                log_unit_debug(u->id, "Redirecting reload request from %s to %s.",
+                log_unit_debug(u->id, "Redirecting reload request from %s to %s.", u->id, following->id);
-                               u->id, following->id);
                 return unit_reload(following);
         }
 

src/core/unit.h

@@ -396,6 +396,10 @@ struct UnitVTable {
         /* Type specific cleanups. */
         void (*shutdown)(Manager *m);
 
+        /* If this function is set and return false all jobs for units
+         * of this type will immediately fail. */
+        bool (*supported)(Manager *m);
+
         /* The interface name */
         const char *bus_interface;
 

src/systemctl/systemctl.c

@@ -2380,12 +2380,18 @@ static int check_wait_response(WaitData *d) {
         assert(d->result);
 
         if (!arg_quiet) {
-                if (streq(d->result, "timeout"))
+                if (streq(d->result, "canceled"))
-                        log_error("Job for %s timed out.", strna(d->name));
-                else if (streq(d->result, "canceled"))
                         log_error("Job for %s canceled.", strna(d->name));
+                else if (streq(d->result, "timeout"))
+                        log_error("Job for %s timed out.", strna(d->name));
                 else if (streq(d->result, "dependency"))
                         log_error("A dependency job for %s failed. See 'journalctl -xe' for details.", strna(d->name));
+                else if (streq(d->result, "invalid"))
+                        log_error("Job for %s invalid.", strna(d->name));
+                else if (streq(d->result, "assert"))
+                        log_error("Assertion failed on job for %s.", strna(d->name));
+                else if (streq(d->result, "unsupported"))
+                        log_error("Operation on or unit type of %s not supported on this system.", strna(d->name));
                 else if (!streq(d->result, "done") && !streq(d->result, "skipped")) {
                         if (d->name) {
                                 bool quotes;
@@ -2400,12 +2406,18 @@ static int check_wait_response(WaitData *d) {
                 }
         }
 
-        if (streq(d->result, "timeout"))
+        if (streq(d->result, "canceled"))
-                r = -ETIME;
-        else if (streq(d->result, "canceled"))
                 r = -ECANCELED;
+        else if (streq(d->result, "timeout"))
+                r = -ETIME;
         else if (streq(d->result, "dependency"))
                 r = -EIO;
+        else if (streq(d->result, "invalid"))
+                r = -ENOEXEC;
+        else if (streq(d->result, "assert"))
+                r = -EPROTO;
+        else if (streq(d->result, "unsupported"))
+                r = -ENOTSUP;
         else if (!streq(d->result, "done") && !streq(d->result, "skipped"))
                 r = -EIO;