Fix extraction of _SYSTEMD_USER_UNIT

Units from user services underneath user@.service would not be detected
properly.

src/shared/cgroup-util.c

@@ -1183,6 +1183,9 @@ int cg_pid_get_unit(pid_t pid, char **unit) {
         return cg_path_get_unit(cgroup, unit);
 }
 
+/**
+ * Skip session-*.scope, but require it to be there.
+ */
 static const char *skip_session(const char *p) {
         size_t n;
 
@@ -1191,7 +1194,27 @@ static const char *skip_session(const char *p) {
         p += strspn(p, "/");
 
         n = strcspn(p, "/");
-        if (n <= 12 || memcmp(p, "session-", 8) != 0 || memcmp(p + n - 6, ".scope", 6) != 0)
+        if (n < strlen("session-x.scope") || memcmp(p, "session-", 8) != 0 || memcmp(p + n - 6, ".scope", 6) != 0)
+                return NULL;
+
+        p += n;
+        p += strspn(p, "/");
+
+        return p;
+}
+
+/**
+ * Skip user@*.service, but require it to be there.
+ */
+static const char *skip_user_manager(const char *p) {
+        size_t n;
+
+        assert(p);
+
+        p += strspn(p, "/");
+
+        n = strcspn(p, "/");
+        if (n < strlen("user@x.service") || memcmp(p, "user@", 5) != 0 || memcmp(p + n - 8, ".service", 8) != 0)
                 return NULL;
 
         p += n;
@@ -1201,7 +1224,7 @@ static const char *skip_session(const char *p) {
 }
 
 int cg_path_get_user_unit(const char *path, char **unit) {
-        const char *e;
+        const char *e, *t;
 
         assert(path);
         assert(unit);
@@ -1213,13 +1236,17 @@ int cg_path_get_user_unit(const char *path, char **unit) {
         /* Skip slices, if there are any */
         e = skip_slices(path);
 
-        /* Skip the session scope, require that there is one */
+        /* Skip the session scope... */
-        e = skip_session(e);
+        t = skip_session(e);
+        if (t)
+                /* ... and skip more slices if there's one */
+                e = skip_slices(t);
+        else {
+                /* ... or require a user manager unit to be there */
+                e = skip_user_manager(e);
                 if (!e)
                         return -ENOENT;
-
+        }
-        /* And skip more slices */
-        e = skip_slices(e);
 
         return cg_path_decode_unit(e, unit);
 }

src/test/test-cgroup-util.c

@@ -27,8 +27,11 @@
 
 static void check_p_d_u(const char *path, int code, const char *result) {
         _cleanup_free_ char *unit = NULL;
+        int r;
 
-        assert_se(cg_path_decode_unit(path, &unit) == code);
+        r = cg_path_decode_unit(path, &unit);
+        printf("%s: %s → %s %d expected %s %d\n", __func__, path, unit, r, result, code);
+        assert_se(r == code);
         assert_se(streq_ptr(unit, result));
 }
 
@@ -46,8 +49,11 @@ static void test_path_decode_unit(void) {
 
 static void check_p_g_u(const char *path, int code, const char *result) {
         _cleanup_free_ char *unit = NULL;
+        int r;
 
-        assert_se(cg_path_get_unit(path, &unit) == code);
+        r = cg_path_get_unit(path, &unit);
+        printf("%s: %s → %s %d expected %s %d\n", __func__, path, unit, r, result, code);
+        assert_se(r == code);
         assert_se(streq_ptr(unit, result));
 }
 
@@ -61,12 +67,17 @@ static void test_path_get_unit(void) {
         check_p_g_u("/system.slice/getty####@tty6.service/xxx", -EINVAL, NULL);
         check_p_g_u("/system.slice/system-waldo.slice/foobar.service/sdfdsaf", 0, "foobar.service");
         check_p_g_u("/system.slice/system-waldo.slice/_cpu.service/sdfdsaf", 0, "cpu.service");
+        check_p_g_u("/user.slice/user-1000.slice/user@1000.service/server.service", 0, "user@1000.service");
+        check_p_g_u("/user.slice/user-1000.slice/user@.service/server.service", -EINVAL, NULL);
 }
 
 static void check_p_g_u_u(const char *path, int code, const char *result) {
         _cleanup_free_ char *unit = NULL;
+        int r;
 
-        assert_se(cg_path_get_user_unit(path, &unit) == code);
+        r = cg_path_get_user_unit(path, &unit);
+        printf("%s: %s → %s %d expected %s %d\n", __func__, path, unit, r, result, code);
+        assert_se(r == code);
         assert_se(streq_ptr(unit, result));
 }
 
@@ -81,6 +92,8 @@ static void test_path_get_user_unit(void) {
         check_p_g_u_u("/xyz.slice/xyz-waldo.slice/session-77.scope/foobar@pie.service/pa/po", 0, "foobar@pie.service");
         check_p_g_u_u("/meh.service", -ENOENT, NULL);
         check_p_g_u_u("/session-3.scope/_cpu.service", 0, "cpu.service");
+        check_p_g_u_u("/user.slice/user-1000.slice/user@1000.service/server.service", 0, "server.service");
+        check_p_g_u_u("/user.slice/user-1000.slice/user@.service/server.service", -ENOENT, NULL);
 }
 
 static void check_p_g_s(const char *path, int code, const char *result) {