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.

4 files changed, 74 insertions, 22 deletions

diff --git a/src/basic/cgroup-util.c b/src/basic/cgroup-util.c
index 7675ab0299..37e6928a46 100644
--- a/src/basic/cgroup-util.c
+++ b/src/basic/cgroup-util.c
@@ -28,6 +28,7 @@
 #include <sys/stat.h>
 #include <sys/statfs.h>
 #include <sys/types.h>
+#include <sys/xattr.h>
 #include <unistd.h>
 
 #include "alloc-util.h"
@@ -883,6 +884,43 @@ int cg_set_task_access(
         return 0;
 }
 
+int cg_set_xattr(const char *controller, const char *path, const char *name, const void *value, size_t size, int flags) {
+        _cleanup_free_ char *fs = NULL;
+        int r;
+
+        assert(path);
+        assert(name);
+        assert(value || size <= 0);
+
+        r = cg_get_path(controller, path, NULL, &fs);
+        if (r < 0)
+                return r;
+
+        if (setxattr(fs, name, value, size, flags) < 0)
+                return -errno;
+
+        return 0;
+}
+
+int cg_get_xattr(const char *controller, const char *path, const char *name, void *value, size_t size) {
+        _cleanup_free_ char *fs = NULL;
+        ssize_t n;
+        int r;
+
+        assert(path);
+        assert(name);
+
+        r = cg_get_path(controller, path, NULL, &fs);
+        if (r < 0)
+                return r;
+
+        n = getxattr(fs, name, value, size);
+        if (n < 0)
+                return -errno;
+
+        return (int) n;
+}
+
 int cg_pid_get_path(const char *controller, pid_t pid, char **path) {
         _cleanup_fclose_ FILE *f = NULL;
         char line[LINE_MAX];
diff --git a/src/basic/cgroup-util.h b/src/basic/cgroup-util.h
index 1a61c7ad22..7529c9719e 100644
--- a/src/basic/cgroup-util.h
+++ b/src/basic/cgroup-util.h
@@ -185,6 +185,9 @@ int cg_get_keyed_attribute(const char *controller, const char *path, const char
 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);
 
+int cg_set_xattr(const char *controller, const char *path, const char *name, const void *value, size_t size, int flags);
+int cg_get_xattr(const char *controller, const char *path, const char *name, void *value, size_t size);
+
 int cg_install_release_agent(const char *controller, const char *agent);
 int cg_uninstall_release_agent(const char *controller);
 
diff --git a/src/basic/log.c b/src/basic/log.c
index 6a8dad311d..bd6c96c4f8 100644
--- a/src/basic/log.c
+++ b/src/basic/log.c
@@ -330,8 +330,6 @@ static int write_to_console(
                 const char *file,
                 int line,
                 const char *func,
-                const char *object_field,
-                const char *object,
                 const char *buffer) {
 
         char location[256], prefix[1 + DECIMAL_STR_MAX(int) + 2];
@@ -390,8 +388,6 @@ static int write_to_syslog(
                 const char *file,
                 int line,
                 const char *func,
-                const char *object_field,
-                const char *object,
                 const char *buffer) {
 
         char header_priority[2 + DECIMAL_STR_MAX(int) + 1],
@@ -453,8 +449,6 @@ static int write_to_kmsg(
                 const char *file,
                 int line,
                 const char *func,
-                const char *object_field,
-                const char *object,
                 const char *buffer) {
 
         char header_priority[2 + DECIMAL_STR_MAX(int) + 1],
@@ -485,7 +479,8 @@ static int log_do_header(
                 int level,
                 int error,
                 const char *file, int line, const char *func,
-                const char *object_field, const char *object) {
+                const char *object_field, const char *object,
+                const char *extra_field, const char *extra) {
 
         snprintf(header, size,
                  "PRIORITY=%i\n"
@@ -495,6 +490,7 @@ static int log_do_header(
                  "%s%s%s"
                  "%s%.*i%s"
                  "%s%s%s"
+                 "%s%s%s"
                  "SYSLOG_IDENTIFIER=%s\n",
                  LOG_PRI(level),
                  LOG_FAC(level),
@@ -513,6 +509,9 @@ static int log_do_header(
                  isempty(object) ? "" : object_field,
                  isempty(object) ? "" : object,
                  isempty(object) ? "" : "\n",
+                 isempty(extra) ? "" : extra_field,
+                 isempty(extra) ? "" : extra,
+                 isempty(extra) ? "" : "\n",
                  program_invocation_short_name);
 
         return 0;
@@ -526,6 +525,8 @@ static int write_to_journal(
                 const char *func,
                 const char *object_field,
                 const char *object,
+                const char *extra_field,
+                const char *extra,
                 const char *buffer) {
 
         char header[LINE_MAX];
@@ -535,7 +536,7 @@ static int write_to_journal(
         if (journal_fd < 0)
                 return 0;
 
-        log_do_header(header, sizeof(header), level, error, file, line, func, object_field, object);
+        log_do_header(header, sizeof(header), level, error, file, line, func, object_field, object, extra_field, extra);
 
         IOVEC_SET_STRING(iovec[0], header);
         IOVEC_SET_STRING(iovec[1], "MESSAGE=");
@@ -559,6 +560,8 @@ static int log_dispatch(
                 const char *func,
                 const char *object_field,
                 const char *object,
+                const char *extra,
+                const char *extra_field,
                 char *buffer) {
 
         assert(buffer);
@@ -589,7 +592,7 @@ static int log_dispatch(
                     log_target == LOG_TARGET_JOURNAL_OR_KMSG ||
                     log_target == LOG_TARGET_JOURNAL) {
 
-                        k = write_to_journal(level, error, file, line, func, object_field, object, buffer);
+                        k = write_to_journal(level, error, file, line, func, object_field, object, extra_field, extra, buffer);
                         if (k < 0) {
                                 if (k != -EAGAIN)
                                         log_close_journal();
@@ -600,7 +603,7 @@ static int log_dispatch(
                 if (log_target == LOG_TARGET_SYSLOG_OR_KMSG ||
                     log_target == LOG_TARGET_SYSLOG) {
 
-                        k = write_to_syslog(level, error, file, line, func, object_field, object, buffer);
+                        k = write_to_syslog(level, error, file, line, func, buffer);
                         if (k < 0) {
                                 if (k != -EAGAIN)
                                         log_close_syslog();
@@ -615,7 +618,7 @@ static int log_dispatch(
                      log_target == LOG_TARGET_JOURNAL_OR_KMSG ||
                      log_target == LOG_TARGET_KMSG)) {
 
-                        k = write_to_kmsg(level, error, file, line, func, object_field, object, buffer);
+                        k = write_to_kmsg(level, error, file, line, func, buffer);
                         if (k < 0) {
                                 log_close_kmsg();
                                 log_open_console();
@@ -623,7 +626,7 @@ static int log_dispatch(
                 }
 
                 if (k <= 0)
-                        (void) write_to_console(level, error, file, line, func, object_field, object, buffer);
+                        (void) write_to_console(level, error, file, line, func, buffer);
 
                 buffer = e;
         } while (buffer);
@@ -649,7 +652,7 @@ int log_dump_internal(
         if (_likely_(LOG_PRI(level) > log_max_level))
                 return -error;
 
-        return log_dispatch(level, error, file, line, func, NULL, NULL, buffer);
+        return log_dispatch(level, error, file, line, func, NULL, NULL, NULL, NULL, buffer);
 }
 
 int log_internalv(
@@ -676,7 +679,7 @@ int log_internalv(
 
         vsnprintf(buffer, sizeof(buffer), format, ap);
 
-        return log_dispatch(level, error, file, line, func, NULL, NULL, buffer);
+        return log_dispatch(level, error, file, line, func, NULL, NULL, NULL, NULL, buffer);
 }
 
 int log_internal(
@@ -705,6 +708,8 @@ int log_object_internalv(
                 const char *func,
                 const char *object_field,
                 const char *object,
+                const char *extra_field,
+                const char *extra,
                 const char *format,
                 va_list ap) {
 
@@ -738,7 +743,7 @@ int log_object_internalv(
 
         vsnprintf(b, l, format, ap);
 
-        return log_dispatch(level, error, file, line, func, object_field, object, buffer);
+        return log_dispatch(level, error, file, line, func, object_field, object, extra_field, extra, buffer);
 }
 
 int log_object_internal(
@@ -749,13 +754,15 @@ int log_object_internal(
                 const char *func,
                 const char *object_field,
                 const char *object,
+                const char *extra_field,
+                const char *extra,
                 const char *format, ...) {
 
         va_list ap;
         int r;
 
         va_start(ap, format);
-        r = log_object_internalv(level, error, file, line, func, object_field, object, format, ap);
+        r = log_object_internalv(level, error, file, line, func, object_field, object, extra_field, extra, format, ap);
         va_end(ap);
 
         return r;
@@ -780,7 +787,7 @@ static void log_assert(
 
         log_abort_msg = buffer;
 
-        log_dispatch(level, 0, file, line, func, NULL, NULL, buffer);
+        log_dispatch(level, 0, file, line, func, NULL, NULL, NULL, NULL, buffer);
 }
 
 noreturn void log_assert_failed(const char *text, const char *file, int line, const char *func) {
@@ -888,7 +895,7 @@ int log_struct_internal(
                 bool fallback = false;
 
                 /* If the journal is available do structured logging */
-                log_do_header(header, sizeof(header), level, error, file, line, func, NULL, NULL);
+                log_do_header(header, sizeof(header), level, error, file, line, func, NULL, NULL, NULL, NULL);
                 IOVEC_SET_STRING(iovec[n++], header);
 
                 va_start(ap, format);
@@ -935,7 +942,7 @@ int log_struct_internal(
         if (!found)
                 return -error;
 
-        return log_dispatch(level, error, file, line, func, NULL, NULL, buf + 8);
+        return log_dispatch(level, error, file, line, func, NULL, NULL, NULL, NULL, buf + 8);
 }
 
 int log_set_target_from_string(const char *e) {
diff --git a/src/basic/log.h b/src/basic/log.h
index b6356228d9..2afee20bb5 100644
--- a/src/basic/log.h
+++ b/src/basic/log.h
@@ -100,18 +100,22 @@ int log_object_internal(
                 const char *func,
                 const char *object_field,
                 const char *object,
-                const char *format, ...) _printf_(8,9);
+                const char *extra_field,
+                const char *extra,
+                const char *format, ...) _printf_(10,11);
 
 int log_object_internalv(
                 int level,
                 int error,
-                const char*file,
+                const char *file,
                 int line,
                 const char *func,
                 const char *object_field,
                 const char *object,
+                const char *extra_field,
+                const char *extra,
                 const char *format,
-                va_list ap) _printf_(8,0);
+                va_list ap) _printf_(9,0);
 
 int log_struct_internal(
                 int level,