core: add a property that shows the current memory usage of a unit

This is exposed the memory.usage_in_bytes cgroup property on the bus,
and makes "systemctl status" show it in its default output.

src/core/dbus-unit.c

@@ -638,10 +638,46 @@ static int property_get_slice(
         return sd_bus_message_append(reply, "s", unit_slice_name(u));
 }
 
+static int property_get_current_memory(
+                sd_bus *bus,
+                const char *path,
+                const char *interface,
+                const char *property,
+                sd_bus_message *reply,
+                void *userdata,
+                sd_bus_error *error) {
+
+        Unit *u = userdata;
+        uint64_t sz = (uint64_t) -1;
+        int r;
+
+        assert(bus);
+        assert(reply);
+        assert(u);
+
+        if (u->cgroup_path &&
+            (u->cgroup_realized_mask & CGROUP_MEMORY)) {
+                _cleanup_free_ char *v = NULL;
+
+                r = cg_get_attribute("memory", u->cgroup_path, "memory.usage_in_bytes", &v);
+                if (r < 0 && r != -ENOENT)
+                        log_unit_warning_errno(u->id, r, "Couldn't read memory.usage_in_bytes attribute: %m");
+
+                if (v) {
+                        r = safe_atou64(v, &sz);
+                        if (r < 0)
+                                log_unit_warning_errno(u->id, r, "Failed to parse memory.usage_in_bytes attribute: %m");
+                }
+        }
+
+        return sd_bus_message_append(reply, "t", sz);
+}
+
 const sd_bus_vtable bus_unit_cgroup_vtable[] = {
         SD_BUS_VTABLE_START(0),
         SD_BUS_PROPERTY("Slice", "s", property_get_slice, 0, 0),
         SD_BUS_PROPERTY("ControlGroup", "s", NULL, offsetof(Unit, cgroup_path), 0),
+        SD_BUS_PROPERTY("MemoryCurrent", "t", property_get_current_memory, 0, 0),
         SD_BUS_VTABLE_END
 };
 

src/shared/cgroup-util.c

@@ -1592,6 +1592,17 @@ int cg_set_attribute(const char *controller, const char *path, const char *attri
         return write_string_file_no_create(p, value);
 }
 
+int cg_get_attribute(const char *controller, const char *path, const char *attribute, char **ret) {
+        _cleanup_free_ char *p = NULL;
+        int r;
+
+        r = cg_get_path(controller, path, attribute, &p);
+        if (r < 0)
+                return r;
+
+        return read_one_line_file(p, ret);
+}
+
 static const char mask_names[] =
         "cpu\0"
         "cpuacct\0"

src/shared/cgroup-util.h

@@ -85,6 +85,7 @@ int cg_attach_fallback(const char *controller, const char *path, pid_t pid);
 int cg_create_and_attach(const char *controller, const char *path, pid_t pid);
 
 int cg_set_attribute(const char *controller, const char *path, const char *attribute, const char *value);
+int cg_get_attribute(const char *controller, const char *path, const char *attribute, char **ret);
 
 int cg_set_group_access(const char *controller, const char *path, mode_t mode, uid_t uid, gid_t gid);
 int cg_set_task_access(const char *controller, const char *path, mode_t mode, uid_t uid, gid_t gid);

src/systemctl/systemctl.c

@@ -3224,6 +3224,10 @@ typedef struct UnitStatusInfo {
         /* Swap */
         const char *what;
 
+        /* CGroup */
+        uint64_t memory_current;
+        uint64_t memory_limit;
+
         LIST_HEAD(ExecStatusInfo, exec);
 } UnitStatusInfo;
 
@@ -3482,6 +3486,17 @@ static void print_status_info(
         if (i->status_errno > 0)
                 printf("    Error: %i (%s)\n", i->status_errno, strerror(i->status_errno));
 
+        if (i->memory_current != (uint64_t) -1) {
+                char buf[FORMAT_BYTES_MAX];
+
+                printf("   Memory: %s", format_bytes(buf, sizeof(buf), i->memory_current));
+
+                if (i->memory_limit != (uint64_t) -1)
+                        printf(" (limit: %s)\n", format_bytes(buf, sizeof(buf), i->memory_limit));
+                else
+                        printf("\n");
+        }
+
         if (i->control_group &&
             (i->main_pid > 0 || i->control_pid > 0 ||
              ((arg_transport != BUS_TRANSPORT_LOCAL && arg_transport != BUS_TRANSPORT_MACHINE) || cg_is_empty_recursive(SYSTEMD_CGROUP_CONTROLLER, i->control_group, false) == 0))) {
@@ -3696,6 +3711,10 @@ static int status_property(const char *name, sd_bus_message *m, UnitStatusInfo *
                         i->condition_timestamp = (usec_t) u;
                 else if (streq(name, "AssertTimestamp"))
                         i->assert_timestamp = (usec_t) u;
+                else if (streq(name, "MemoryCurrent"))
+                        i->memory_current = u;
+                else if (streq(name, "MemoryLimit"))
+                        i->memory_limit = u;
 
                 break;
         }
@@ -4166,7 +4185,10 @@ static int show_one(
 
         _cleanup_bus_message_unref_ sd_bus_message *reply = NULL;
         _cleanup_bus_error_free_ sd_bus_error error = SD_BUS_ERROR_NULL;
-        UnitStatusInfo info = {};
+        UnitStatusInfo info = {
+                .memory_current = (uint64_t) -1,
+                .memory_limit = (uint64_t) -1,
+        };
         ExecStatusInfo *p;
         int r;