login: add an api to determine the slice a PID is located in to libsystemd-login

src/login/libsystemd-login.sym

@@ -75,3 +75,8 @@ LIBSYSTEMD_LOGIN_203 {
 global:
         sd_get_machine_names;
 } LIBSYSTEMD_LOGIN_202;
+
+LIBSYSTEMD_LOGIN_204 {
+global:
+        sd_pid_get_slice;
+} LIBSYSTEMD_LOGIN_203;

src/login/sd-login.c

@@ -72,6 +72,16 @@ _public_ int sd_pid_get_machine_name(pid_t pid, char **name) {
         return cg_pid_get_machine_name(pid, name);
 }
 
+_public_ int sd_pid_get_slice(pid_t pid, char **slice) {
+
+        if (pid < 0)
+                return -EINVAL;
+        if (!slice)
+                return -EINVAL;
+
+        return cg_pid_get_slice(pid, slice);
+}
+
 _public_ int sd_pid_get_owner_uid(pid_t pid, uid_t *uid) {
 
         if (pid < 0)

src/shared/cgroup-util.c

@@ -1227,11 +1227,11 @@ int cg_path_decode_unit(const char *cgroup, char **unit){
 }
 
 static const char *skip_slices(const char *p) {
-        size_t n;
-
         /* Skips over all slice assignments */
 
         for (;;) {
+                size_t n;
+
                 p += strspn(p, "/");
 
                 n = strcspn(p, "/");
@@ -1475,6 +1475,53 @@ int cg_pid_get_owner_uid(pid_t pid, uid_t *uid) {
         return cg_path_get_owner_uid(cgroup, uid);
 }
 
+int cg_path_get_slice(const char *p, char **slice) {
+        const char *e = NULL;
+        size_t m = 0;
+
+        assert(p);
+        assert(slice);
+
+        for (;;) {
+                size_t n;
+
+                p += strspn(p, "/");
+
+                n = strcspn(p, "/");
+                if (n <= 6 || memcmp(p + n - 6, ".slice", 6) != 0) {
+                        char *s;
+
+                        if (!e)
+                                return -ENOENT;
+
+                        s = strndup(e, m);
+                        if (!s)
+                                return -ENOMEM;
+
+                        *slice = s;
+                        return 0;
+                }
+
+                e = p;
+                m = n;
+
+                p += n;
+        }
+}
+
+int cg_pid_get_slice(pid_t pid, char **slice) {
+        _cleanup_free_ char *cgroup = NULL;
+        int r;
+
+        assert(slice);
+
+        r = cg_pid_get_path_shifted(pid, NULL, &cgroup);
+        if (r < 0)
+                return r;
+
+        return cg_path_get_slice(cgroup, slice);
+}
+
 int cg_controller_from_attr(const char *attr, char **controller) {
         const char *dot;
         char *c;

src/shared/cgroup-util.h

@@ -90,6 +90,7 @@ int cg_path_get_owner_uid(const char *path, uid_t *uid);
 int cg_path_get_unit(const char *path, char **unit);
 int cg_path_get_user_unit(const char *path, char **unit);
 int cg_path_get_machine_name(const char *path, char **machine);
+int cg_path_get_slice(const char *path, char **slice);
 
 int cg_pid_get_path_shifted(pid_t pid, char **root, char **cgroup);
 
@@ -98,6 +99,7 @@ int cg_pid_get_owner_uid(pid_t pid, uid_t *uid);
 int cg_pid_get_unit(pid_t pid, char **unit);
 int cg_pid_get_user_unit(pid_t pid, char **unit);
 int cg_pid_get_machine_name(pid_t pid, char **machine);
+int cg_pid_get_slice(pid_t pid, char **slice);
 
 int cg_path_decode_unit(const char *cgroup, char **unit);
 

src/systemd/sd-login.h

@@ -72,9 +72,12 @@ int sd_pid_get_unit(pid_t pid, char **unit);
 int sd_pid_get_user_unit(pid_t pid, char **unit);
 
 /* Get machine name from PID, for processes assigned to VM or
- * container. This will return an error for non-service processes. */
+ * container. This will return an error for non-machine processes. */
 int sd_pid_get_machine_name(pid_t pid, char **name);
 
+/* Get slice name from PID. */
+int sd_pid_get_slice(pid_t pid, char **name);
+
 /* Get state from uid. Possible states: offline, lingering, online, active, closing */
 int sd_uid_get_state(uid_t uid, char**state);
 

src/test/test-cgroup-util.c

@@ -134,7 +134,7 @@ static void test_proc(void) {
         assert_se(d);
 
         FOREACH_DIRENT(de, d, break) {
-                _cleanup_free_ char *path = NULL, *path_shifted = NULL, *session = NULL, *unit = NULL, *user_unit = NULL, *machine = NULL, *prefix = NULL;
+                _cleanup_free_ char *path = NULL, *path_shifted = NULL, *session = NULL, *unit = NULL, *user_unit = NULL, *machine = NULL, *prefix = NULL, *slice = NULL;
                 pid_t pid;
                 uid_t uid = (uid_t) -1;
 
@@ -156,8 +156,9 @@ static void test_proc(void) {
                 cg_pid_get_unit(pid, &unit);
                 cg_pid_get_user_unit(pid, &user_unit);
                 cg_pid_get_machine_name(pid, &machine);
+                cg_pid_get_slice(pid, &slice);
 
-                printf("%lu\t%s\t%s\t%s\t%lu\t%s\t%s\t%s\t%s\n",
+                printf("%lu\t%s\t%s\t%s\t%lu\t%s\t%s\t%s\t%s\t%s\n",
                        (unsigned long) pid,
                        path,
                        prefix,
@@ -166,7 +167,8 @@ static void test_proc(void) {
                        session,
                        unit,
                        user_unit,
-                       machine);
+                       machine,
+                       slice);
         }
 }