logind: add infrastructure to keep track of machines, and move to slices

- This changes all logind cgroup objects to use slice objects rather
  than fixed croup locations.

- logind can now collect minimal information about running
  VMs/containers. As fixed cgroup locations can no longer be used we
  need an entity that keeps track of machine cgroups in whatever slice
  they might be located. Since logind already keeps track of users,
  sessions and seats this is a trivial addition.

- nspawn will now register with logind and pass various bits of metadata
  along. A new option "--slice=" has been added to place the container
  in a specific slice.

- loginctl gained commands to list, introspect and terminate machines.

- user.slice and machine.slice will now be pulled in by logind.service,
  since only logind.service requires this slice.

1 files changed, 29 insertions, 40 deletions

diff --git a/src/core/cgroup.c b/src/core/cgroup.c
index a995d1436d..5065329739 100644
--- a/src/core/cgroup.c
+++ b/src/core/cgroup.c
@@ -32,6 +32,7 @@
 #include "log.h"
 #include "strv.h"
 #include "path-util.h"
+#include "special.h"
 
 int cgroup_bonding_realize(CGroupBonding *b) {
         int r;
@@ -304,7 +305,8 @@ int cgroup_bonding_is_empty_list(CGroupBonding *first) {
         LIST_FOREACH(by_unit, b, first) {
                 int r;
 
-                if ((r = cgroup_bonding_is_empty(b)) < 0) {
+                r = cgroup_bonding_is_empty(b);
+                if (r < 0) {
                         /* If this returned -EAGAIN, then we don't know if the
                          * group is empty, so let's see if another group can
                          * tell us */
@@ -319,10 +321,9 @@ int cgroup_bonding_is_empty_list(CGroupBonding *first) {
 }
 
 int manager_setup_cgroup(Manager *m) {
-        _cleanup_free_ char *current = NULL, *path = NULL;
-        char suffix_buffer[sizeof("/systemd-") + DECIMAL_STR_MAX(pid_t)];
-        const char *suffix;
+        _cleanup_free_ char *path = NULL;
         int r;
+        char *e, *a;
 
         assert(m);
 
@@ -333,37 +334,30 @@ int manager_setup_cgroup(Manager *m) {
         }
 
         /* 1. Determine hierarchy */
-        r = cg_pid_get_path(SYSTEMD_CGROUP_CONTROLLER, 0, &current);
+        free(m->cgroup_root);
+        m->cgroup_root = NULL;
+
+        r = cg_pid_get_path(SYSTEMD_CGROUP_CONTROLLER, 0, &m->cgroup_root);
         if (r < 0) {
                 log_error("Cannot determine cgroup we are running in: %s", strerror(-r));
                 return r;
         }
 
-        if (m->running_as == SYSTEMD_SYSTEM)
-                suffix = NULL;
-        else {
-                sprintf(suffix_buffer, "/systemd-%lu", (unsigned long) getpid());
-                suffix = suffix_buffer;
+        /* Already in /system.slice? If so, let's cut this off again */
+        if (m->running_as == SYSTEMD_SYSTEM) {
+                e = endswith(m->cgroup_root, "/" SPECIAL_SYSTEM_SLICE);
+                if (e)
+                        *e = 0;
         }
 
-        free(m->cgroup_hierarchy);
-        if (!suffix || endswith(current, suffix)) {
-                /* We probably got reexecuted and can continue to use our root cgroup */
-                m->cgroup_hierarchy = current;
-                current = NULL;
-        } else {
-                /* We need a new root cgroup */
-                if (streq(current, "/"))
-                        m->cgroup_hierarchy = strdup(suffix);
-                else
-                        m->cgroup_hierarchy = strappend(current, suffix);
-
-                if (!m->cgroup_hierarchy)
-                        return log_oom();
-        }
+        /* And make sure to store away the root value without trailing
+         * slash, even for the root dir, so that we can easily prepend
+         * it everywhere. */
+        if (streq(m->cgroup_root, "/"))
+                m->cgroup_root[0] = 0;
 
         /* 2. Show data */
-        r = cg_get_path(SYSTEMD_CGROUP_CONTROLLER, m->cgroup_hierarchy, NULL, &path);
+        r = cg_get_path(SYSTEMD_CGROUP_CONTROLLER, m->cgroup_root, NULL, &path);
         if (r < 0) {
                 log_error("Cannot find cgroup mount point: %s", strerror(-r));
                 return r;
@@ -382,8 +376,9 @@ int manager_setup_cgroup(Manager *m) {
                         log_debug("Release agent already installed.");
         }
 
-        /* 4. Realize the group */
-        r = cg_create_and_attach(SYSTEMD_CGROUP_CONTROLLER, m->cgroup_hierarchy, 0);
+        /* 4. Realize the system slice and put us in there */
+        a = strappenda(m->cgroup_root, "/" SPECIAL_SYSTEM_SLICE);
+        r = cg_create_and_attach(SYSTEMD_CGROUP_CONTROLLER, a, 0);
         if (r < 0) {
                 log_error("Failed to create root cgroup hierarchy: %s", strerror(-r));
                 return r;
@@ -402,30 +397,24 @@ int manager_setup_cgroup(Manager *m) {
         /* 6. Remove non-existing controllers from the default controllers list */
         cg_shorten_controllers(m->default_controllers);
 
-        /* 7. Let's create the user and machine hierarchies
-         * right-away, so that people can inotify on them, if they
-         * wish, without this being racy. */
-        if (m->running_as == SYSTEMD_SYSTEM) {
-                cg_create(SYSTEMD_CGROUP_CONTROLLER, m->cgroup_hierarchy, "../user");
-                cg_create(SYSTEMD_CGROUP_CONTROLLER, m->cgroup_hierarchy, "../machine");
-        }
-
         return 0;
 }
 
 void manager_shutdown_cgroup(Manager *m, bool delete) {
         assert(m);
 
-        if (delete && m->cgroup_hierarchy)
-                cg_delete(SYSTEMD_CGROUP_CONTROLLER, m->cgroup_hierarchy);
+        /* We can't really delete the group, since we are in it. But
+         * let's trim it. */
+        if (delete && m->cgroup_root)
+                cg_trim(SYSTEMD_CGROUP_CONTROLLER, m->cgroup_root, false);
 
         if (m->pin_cgroupfs_fd >= 0) {
                 close_nointr_nofail(m->pin_cgroupfs_fd);
                 m->pin_cgroupfs_fd = -1;
         }
 
-        free(m->cgroup_hierarchy);
-        m->cgroup_hierarchy = NULL;
+        free(m->cgroup_root);
+        m->cgroup_root = NULL;
 }
 
 int cgroup_bonding_get(Manager *m, const char *cgroup, CGroupBonding **bonding) {