core: add "invocation ID" concept to service manager

This adds a new invocation ID concept to the service manager. The invocation ID
identifies each runtime cycle of a unit uniquely. A new randomized 128bit ID is
generated each time a unit moves from and inactive to an activating or active
state.

The primary usecase for this concept is to connect the runtime data PID 1
maintains about a service with the offline data the journal stores about it.
Previously we'd use the unit name plus start/stop times, which however is
highly racy since the journal will generally process log data after the service
already ended.

The "invocation ID" kinda matches the "boot ID" concept of the Linux kernel,
except that it applies to an individual unit instead of the whole system.

The invocation ID is passed to the activated processes as environment variable.
It is additionally stored as extended attribute on the cgroup of the unit. The
latter is used by journald to automatically retrieve it for each log logged
message and attach it to the log entry. The environment variable is very easily
accessible, even for unprivileged services. OTOH the extended attribute is only
accessible to privileged processes (this is because cgroupfs only supports the
"trusted." xattr namespace, not "user."). The environment variable may be
altered by services, the extended attribute may not be, hence is the better
choice for the journal.

Note that reading the invocation ID off the extended attribute from journald is
racy, similar to the way reading the unit name for a logging process is.

This patch adds APIs to read the invocation ID to sd-id128:
sd_id128_get_invocation() may be used in a similar fashion to
sd_id128_get_boot().

PID1's own logging is updated to always include the invocation ID when it logs
information about a unit.

A new bus call GetUnitByInvocationID() is added that allows retrieving a bus
path to a unit by its invocation ID. The bus path is built using the invocation
ID, thus providing a path for referring to a unit that is valid only for the
current runtime cycleof it.

Outlook for the future: should the kernel eventually allow passing of cgroup
information along AF_UNIX/SOCK_DGRAM messages via a unique cgroup id, then we
can alter the invocation ID to be generated as hash from that rather than
entirely randomly. This way we can derive the invocation race-freely from the
messages.

1 files changed, 72 insertions, 19 deletions

diff --git a/src/core/cgroup.c b/src/core/cgroup.c
index e55b54633..ccdab64a6 100644
--- a/src/core/cgroup.c
+++ b/src/core/cgroup.c
@@ -67,6 +67,7 @@ void cgroup_context_init(CGroupContext *c) {
 
         c->memory_high = CGROUP_LIMIT_MAX;
         c->memory_max = CGROUP_LIMIT_MAX;
+        c->memory_swap_max = CGROUP_LIMIT_MAX;
 
         c->memory_limit = CGROUP_LIMIT_MAX;
 
@@ -174,6 +175,7 @@ void cgroup_context_dump(CGroupContext *c, FILE* f, const char *prefix) {
                 "%sMemoryLow=%" PRIu64 "\n"
                 "%sMemoryHigh=%" PRIu64 "\n"
                 "%sMemoryMax=%" PRIu64 "\n"
+                "%sMemorySwapMax=%" PRIu64 "\n"
                 "%sMemoryLimit=%" PRIu64 "\n"
                 "%sTasksMax=%" PRIu64 "\n"
                 "%sDevicePolicy=%s\n"
@@ -195,6 +197,7 @@ void cgroup_context_dump(CGroupContext *c, FILE* f, const char *prefix) {
                 prefix, c->memory_low,
                 prefix, c->memory_high,
                 prefix, c->memory_max,
+                prefix, c->memory_swap_max,
                 prefix, c->memory_limit,
                 prefix, c->tasks_max,
                 prefix, cgroup_device_policy_to_string(c->device_policy),
@@ -618,7 +621,7 @@ static unsigned cgroup_apply_blkio_device_limit(Unit *u, const char *dev_path, u
 }
 
 static bool cgroup_context_has_unified_memory_config(CGroupContext *c) {
-        return c->memory_low > 0 || c->memory_high != CGROUP_LIMIT_MAX || c->memory_max != CGROUP_LIMIT_MAX;
+        return c->memory_low > 0 || c->memory_high != CGROUP_LIMIT_MAX || c->memory_max != CGROUP_LIMIT_MAX || c->memory_swap_max != CGROUP_LIMIT_MAX;
 }
 
 static void cgroup_apply_unified_memory_limit(Unit *u, const char *file, uint64_t v) {
@@ -666,7 +669,7 @@ static void cgroup_context_apply(Unit *u, CGroupMask mask, ManagerState state) {
                 bool has_weight = cgroup_context_has_cpu_weight(c);
                 bool has_shares = cgroup_context_has_cpu_shares(c);
 
-                if (cg_unified() > 0) {
+                if (cg_all_unified() > 0) {
                         uint64_t weight;
 
                         if (has_weight)
@@ -847,12 +850,14 @@ static void cgroup_context_apply(Unit *u, CGroupMask mask, ManagerState state) {
         }
 
         if ((mask & CGROUP_MASK_MEMORY) && !is_root) {
-                if (cg_unified() > 0) {
+                if (cg_all_unified() > 0) {
                         uint64_t max = c->memory_max;
+                        uint64_t swap_max = c->memory_swap_max;
 
-                        if (cgroup_context_has_unified_memory_config(c))
+                        if (cgroup_context_has_unified_memory_config(c)) {
                                 max = c->memory_max;
-                        else {
+                                swap_max = c->memory_swap_max;
+                        } else {
                                 max = c->memory_limit;
 
                                 if (max != CGROUP_LIMIT_MAX)
@@ -862,6 +867,7 @@ static void cgroup_context_apply(Unit *u, CGroupMask mask, ManagerState state) {
                         cgroup_apply_unified_memory_limit(u, "memory.low", c->memory_low);
                         cgroup_apply_unified_memory_limit(u, "memory.high", c->memory_high);
                         cgroup_apply_unified_memory_limit(u, "memory.max", max);
+                        cgroup_apply_unified_memory_limit(u, "memory.swap.max", swap_max);
                 } else {
                         char buf[DECIMAL_STR_MAX(uint64_t) + 1];
                         uint64_t val = c->memory_limit;
@@ -1021,7 +1027,7 @@ CGroupMask unit_get_own_mask(Unit *u) {
                 e = unit_get_exec_context(u);
                 if (!e ||
                     exec_context_maintains_privileges(e) ||
-                    cg_unified() > 0)
+                    cg_all_unified() > 0)
                         return _CGROUP_MASK_ALL;
         }
 
@@ -1247,7 +1253,7 @@ int unit_watch_cgroup(Unit *u) {
                 return 0;
 
         /* Only applies to the unified hierarchy */
-        r = cg_unified();
+        r = cg_unified(SYSTEMD_CGROUP_CONTROLLER);
         if (r < 0)
                 return log_unit_error_errno(u, r, "Failed detect whether the unified hierarchy is used: %m");
         if (r == 0)
@@ -1357,6 +1363,26 @@ int unit_attach_pids_to_cgroup(Unit *u) {
         return 0;
 }
 
+static void cgroup_xattr_apply(Unit *u) {
+        char ids[SD_ID128_STRING_MAX];
+        int r;
+
+        assert(u);
+
+        if (!MANAGER_IS_SYSTEM(u->manager))
+                return;
+
+        if (sd_id128_is_null(u->invocation_id))
+                return;
+
+        r = cg_set_xattr(SYSTEMD_CGROUP_CONTROLLER, u->cgroup_path,
+                         "trusted.invocation_id",
+                         sd_id128_to_string(u->invocation_id, ids), 32,
+                         0);
+        if (r < 0)
+                log_unit_warning_errno(u, r, "Failed to set invocation ID on control group %s, ignoring: %m", u->cgroup_path);
+}
+
 static bool unit_has_mask_realized(Unit *u, CGroupMask target_mask, CGroupMask enable_mask) {
         assert(u);
 
@@ -1400,6 +1426,7 @@ static int unit_realize_cgroup_now(Unit *u, ManagerState state) {
 
         /* Finally, apply the necessary attributes. */
         cgroup_context_apply(u, target_mask, state);
+        cgroup_xattr_apply(u);
 
         return 0;
 }
@@ -1526,6 +1553,8 @@ void unit_prune_cgroup(Unit *u) {
         if (!u->cgroup_path)
                 return;
 
+        (void) unit_get_cpu_usage(u, NULL); /* Cache the last CPU usage value before we destroy the cgroup */
+
         is_root_slice = unit_has_name(u, SPECIAL_ROOT_SLICE);
 
         r = cg_trim_everywhere(u->manager->cgroup_supported, u->cgroup_path, !is_root_slice);
@@ -1647,7 +1676,7 @@ int unit_watch_all_pids(Unit *u) {
         if (!u->cgroup_path)
                 return -ENOENT;
 
-        if (cg_unified() > 0) /* On unified we can use proper notifications */
+        if (cg_unified(SYSTEMD_CGROUP_CONTROLLER) > 0) /* On unified we can use proper notifications */
                 return 0;
 
         return unit_watch_pids_in_path(u, u->cgroup_path);
@@ -1721,7 +1750,7 @@ static int on_cgroup_inotify_event(sd_event_source *s, int fd, uint32_t revents,
 int manager_setup_cgroup(Manager *m) {
         _cleanup_free_ char *path = NULL;
         CGroupController c;
-        int r, unified;
+        int r, all_unified, systemd_unified;
         char *e;
 
         assert(m);
@@ -1762,11 +1791,17 @@ int manager_setup_cgroup(Manager *m) {
         if (r < 0)
                 return log_error_errno(r, "Cannot find cgroup mount point: %m");
 
-        unified = cg_unified();
-        if (unified < 0)
-                return log_error_errno(r, "Couldn't determine if we are running in the unified hierarchy: %m");
-        if (unified > 0)
+        all_unified = cg_all_unified();
+        systemd_unified = cg_unified(SYSTEMD_CGROUP_CONTROLLER);
+
+        if (all_unified < 0 || systemd_unified < 0)
+                return log_error_errno(all_unified < 0 ? all_unified : systemd_unified,
+                                       "Couldn't determine if we are running in the unified hierarchy: %m");
+
+        if (all_unified > 0)
                 log_debug("Unified cgroup hierarchy is located at %s.", path);
+        else if (systemd_unified > 0)
+                log_debug("Unified cgroup hierarchy is located at %s. Controllers are on legacy hierarchies.", path);
         else
                 log_debug("Using cgroup controller " SYSTEMD_CGROUP_CONTROLLER ". File system hierarchy is at %s.", path);
 
@@ -1774,7 +1809,7 @@ int manager_setup_cgroup(Manager *m) {
                 const char *scope_path;
 
                 /* 3. Install agent */
-                if (unified) {
+                if (systemd_unified) {
 
                         /* In the unified hierarchy we can get
                          * cgroup empty notifications via inotify. */
@@ -1852,7 +1887,7 @@ int manager_setup_cgroup(Manager *m) {
                         return log_error_errno(errno, "Failed to open pin file: %m");
 
                 /* 6.  Always enable hierarchical support if it exists... */
-                if (!unified)
+                if (!all_unified)
                         (void) cg_set_attribute("memory", "/", "memory.use_hierarchy", "1");
         }
 
@@ -1989,7 +2024,6 @@ int manager_notify_cgroup_empty(Manager *m, const char *cgroup) {
         return 0;
 }
 #endif // 0
-
 #if 0 /// UNNEEDED by elogind
 int unit_get_memory_current(Unit *u, uint64_t *ret) {
         _cleanup_free_ char *v = NULL;
@@ -2004,7 +2038,7 @@ int unit_get_memory_current(Unit *u, uint64_t *ret) {
         if ((u->cgroup_realized_mask & CGROUP_MASK_MEMORY) == 0)
                 return -ENODATA;
 
-        if (cg_unified() <= 0)
+        if (cg_all_unified() <= 0)
                 r = cg_get_attribute("memory", u->cgroup_path, "memory.usage_in_bytes", &v);
         else
                 r = cg_get_attribute("memory", u->cgroup_path, "memory.current", &v);
@@ -2049,7 +2083,7 @@ static int unit_get_cpu_usage_raw(Unit *u, nsec_t *ret) {
         if (!u->cgroup_path)
                 return -ENODATA;
 
-        if (cg_unified() > 0) {
+        if (cg_all_unified() > 0) {
                 const char *keys[] = { "usage_usec", NULL };
                 _cleanup_free_ char *val = NULL;
                 uint64_t us;
@@ -2089,7 +2123,21 @@ int unit_get_cpu_usage(Unit *u, nsec_t *ret) {
         nsec_t ns;
         int r;
 
+        assert(u);
+
+        /* Retrieve the current CPU usage counter. This will subtract the CPU counter taken when the unit was
+         * started. If the cgroup has been removed already, returns the last cached value. To cache the value, simply
+         * call this function with a NULL return value. */
+
         r = unit_get_cpu_usage_raw(u, &ns);
+        if (r == -ENODATA && u->cpu_usage_last != NSEC_INFINITY) {
+                /* If we can't get the CPU usage anymore (because the cgroup was already removed, for example), use our
+                 * cached value. */
+
+                if (ret)
+                        *ret = u->cpu_usage_last;
+                return 0;
+        }
         if (r < 0)
                 return r;
 
@@ -2098,7 +2146,10 @@ int unit_get_cpu_usage(Unit *u, nsec_t *ret) {
         else
                 ns = 0;
 
-        *ret = ns;
+        u->cpu_usage_last = ns;
+        if (ret)
+                *ret = ns;
+
         return 0;
 }
 
@@ -2108,6 +2159,8 @@ int unit_reset_cpu_usage(Unit *u) {
 
         assert(u);
 
+        u->cpu_usage_last = NSEC_INFINITY;
+
         r = unit_get_cpu_usage_raw(u, &ns);
         if (r < 0) {
                 u->cpu_usage_base = 0;