specifier: rework specifier calls to return proper error message

Previously the specifier calls could only indicate OOM by returning
NULL. With this change they will return negative errno-style error codes
like everything else.

5 files changed, 250 insertions, 152 deletions

diff --git a/src/core/load-fragment.c b/src/core/load-fragment.c
index f4a268c1ef..cfc6f078a6 100644
--- a/src/core/load-fragment.c
+++ b/src/core/load-fragment.c
@@ -99,9 +99,12 @@ int config_parse_unit_deps(const char* unit,
                 if (!t)
                         return log_oom();
 
-                k = unit_name_printf(u, t);
-                if (!k)
-                        return log_oom();
+                r = unit_name_printf(u, t, &k);
+                if (r < 0) {
+                        log_syntax(unit, LOG_ERR, filename, line, -r,
+                                   "Failed to resolve specifiers, ignoring: %s", strerror(-r));
+                        continue;
+                }
 
                 r = unit_add_dependency_by_name(u, d, k, NULL, true);
                 if (r < 0)
@@ -124,16 +127,17 @@ int config_parse_unit_string_printf(const char *unit,
 
         Unit *u = userdata;
         _cleanup_free_ char *k = NULL;
+        int r;
 
         assert(filename);
         assert(lvalue);
         assert(rvalue);
         assert(u);
 
-        k = unit_full_printf(u, rvalue);
-        if (!k)
-                log_syntax(unit, LOG_ERR, filename, line, EINVAL,
-                           "Failed to resolve unit specifiers on %s. Ignoring.", rvalue);
+        r = unit_full_printf(u, rvalue, &k);
+        if (r < 0)
+                log_syntax(unit, LOG_ERR, filename, line, -r,
+                           "Failed to resolve unit specifiers on %s, ignoring: %s", rvalue, strerror(-r));
 
         return config_parse_string(unit, filename, line, section, lvalue, ltype,
                                    k ? k : rvalue, data, userdata);
@@ -151,16 +155,17 @@ int config_parse_unit_strv_printf(const char *unit,
 
         Unit *u = userdata;
         _cleanup_free_ char *k = NULL;
+        int r;
 
         assert(filename);
         assert(lvalue);
         assert(rvalue);
         assert(u);
 
-        k = unit_full_printf(u, rvalue);
-        if (!k)
-                log_syntax(unit, LOG_ERR, filename, line, EINVAL,
-                           "Failed to resolve unit specifiers on %s. Ignoring.", rvalue);
+        r = unit_full_printf(u, rvalue, &k);
+        if (r < 0)
+                log_syntax(unit, LOG_ERR, filename, line, -r,
+                           "Failed to resolve unit specifiers on %s, ignoring: %s", rvalue, strerror(-r));
 
         return config_parse_strv(unit, filename, line, section, lvalue, ltype,
                                  k ? k : rvalue, data, userdata);
@@ -178,16 +183,17 @@ int config_parse_unit_path_printf(const char *unit,
 
         Unit *u = userdata;
         _cleanup_free_ char *k = NULL;
+        int r;
 
         assert(filename);
         assert(lvalue);
         assert(rvalue);
         assert(u);
 
-        k = unit_full_printf(u, rvalue);
-        if (!k)
-                log_syntax(unit, LOG_ERR, filename, line, EINVAL,
-                           "Failed to resolve unit specifiers on %s. Ignoring.", rvalue);
+        r = unit_full_printf(u, rvalue, &k);
+        if (r < 0)
+                log_syntax(unit, LOG_ERR, filename, line, -r,
+                           "Failed to resolve unit specifiers on %s, ignoring: %s", rvalue, strerror(-r));
 
         return config_parse_path(unit, filename, line, section, lvalue, ltype,
                                  k ? k : rvalue, data, userdata);
@@ -205,6 +211,7 @@ int config_parse_socket_listen(const char *unit,
 
         SocketPort *p, *tail;
         Socket *s;
+        int r;
 
         assert(filename);
         assert(lvalue);
@@ -226,32 +233,31 @@ int config_parse_socket_listen(const char *unit,
         if (ltype != SOCKET_SOCKET) {
 
                 p->type = ltype;
-                p->path = unit_full_printf(UNIT(s), rvalue);
-                if (!p->path) {
+                r = unit_full_printf(UNIT(s), rvalue, &p->path);
+                if (r < 0) {
                         p->path = strdup(rvalue);
                         if (!p->path) {
                                 free(p);
                                 return log_oom();
                         } else
-                                log_syntax(unit, LOG_ERR, filename, line, EINVAL,
-                                           "Failed to resolve unit specifiers on %s. Ignoring.", rvalue);
+                                log_syntax(unit, LOG_ERR, filename, line, -r,
+                                           "Failed to resolve unit specifiers on %s, ignoring: %s", rvalue, strerror(-r));
                 }
 
                 path_kill_slashes(p->path);
 
         } else if (streq(lvalue, "ListenNetlink")) {
                 _cleanup_free_ char  *k = NULL;
-                int r;
 
                 p->type = SOCKET_SOCKET;
-                k = unit_full_printf(UNIT(s), rvalue);
-                if (!k)
-                        log_syntax(unit, LOG_ERR, filename, line, EINVAL,
-                                   "Failed to resolve unit specifiers on %s. Ignoring.", rvalue);
+                r = unit_full_printf(UNIT(s), rvalue, &k);
+                if (r < 0)
+                        log_syntax(unit, LOG_ERR, filename, line, -r,
+                                   "Failed to resolve unit specifiers on %s, ignoring: %s", rvalue, strerror(-r));
 
                 r = socket_address_parse_netlink(&p->address, k ? k : rvalue);
                 if (r < 0) {
-                        log_syntax(unit, LOG_ERR, filename, line, EINVAL,
+                        log_syntax(unit, LOG_ERR, filename, line, -r,
                                    "Failed to parse address value, ignoring: %s", rvalue);
                         free(p);
                         return 0;
@@ -259,17 +265,16 @@ int config_parse_socket_listen(const char *unit,
 
         } else {
                 _cleanup_free_ char *k = NULL;
-                int r;
 
                 p->type = SOCKET_SOCKET;
-                k = unit_full_printf(UNIT(s), rvalue);
-                if (!k)
-                        log_syntax(unit, LOG_ERR, filename, line, EINVAL,
-                                   "Failed to resolve unit specifiers on %s. Ignoring.", rvalue);
+                r = unit_full_printf(UNIT(s), rvalue, &k);
+                if (r < 0)
+                        log_syntax(unit, LOG_ERR, filename, line, -r,
+                                   "Failed to resolve unit specifiers on %s, ignoring: %s", rvalue, strerror(-r));
 
                 r = socket_address_parse(&p->address, k ? k : rvalue);
                 if (r < 0) {
-                        log_syntax(unit, LOG_ERR, filename, line, EINVAL,
+                        log_syntax(unit, LOG_ERR, filename, line, -r,
                                    "Failed to parse address value, ignoring: %s", rvalue);
                         free(p);
                         return 0;
@@ -1230,11 +1235,12 @@ int config_parse_trigger_unit(
                 return 0;
         }
 
-        p = unit_name_printf(u, rvalue);
-        if (!p)
-                return log_oom();
+        r = unit_name_printf(u, rvalue, &p);
+        if (r < 0)
+                log_syntax(unit, LOG_ERR, filename, line, -r,
+                           "Failed to resolve specifiers, ignoring: %s", strerror(-r));
 
-        type = unit_name_to_type(p);
+        type = unit_name_to_type(p ?: rvalue);
         if (type < 0) {
                 log_syntax(unit, LOG_ERR, filename, line, EINVAL,
                            "Unit type not valid, ignoring: %s", rvalue);
@@ -1247,10 +1253,10 @@ int config_parse_trigger_unit(
                 return 0;
         }
 
-        r = unit_add_two_dependencies_by_name(u, UNIT_BEFORE, UNIT_TRIGGERS, p, NULL, true);
+        r = unit_add_two_dependencies_by_name(u, UNIT_BEFORE, UNIT_TRIGGERS, p ?: rvalue, NULL, true);
         if (r < 0) {
                 log_syntax(unit, LOG_ERR, filename, line, -r,
-                           "Failed to add trigger on %s, ignoring: %s", p, strerror(-r));
+                           "Failed to add trigger on %s, ignoring: %s", p ?: rvalue, strerror(-r));
                 return 0;
         }
 
@@ -1271,6 +1277,7 @@ int config_parse_path_spec(const char *unit,
         PathSpec *s;
         PathType b;
         _cleanup_free_ char *k = NULL;
+        int r;
 
         assert(filename);
         assert(lvalue);
@@ -1290,13 +1297,13 @@ int config_parse_path_spec(const char *unit,
                 return 0;
         }
 
-        k = unit_full_printf(UNIT(p), rvalue);
-        if (!k) {
+        r = unit_full_printf(UNIT(p), rvalue, &k);
+        if (r < 0) {
                 k = strdup(rvalue);
                 if (!k)
                         return log_oom();
                 else
-                        log_syntax(unit, LOG_ERR, filename, line, EINVAL,
+                        log_syntax(unit, LOG_ERR, filename, line, -r,
                                    "Failed to resolve unit specifiers on %s. Ignoring.",
                                    rvalue);
         }
@@ -1344,19 +1351,20 @@ int config_parse_socket_service(const char *unit,
 
         dbus_error_init(&error);
 
-        p = unit_name_printf(UNIT(s), rvalue);
-        if (!p)
-                return log_oom();
+        r = unit_name_printf(UNIT(s), rvalue, &p);
+        if (r < 0)
+                log_syntax(unit, LOG_ERR, filename, line, -r,
+                           "Failed to resolve specifiers, ignoring: %s", rvalue);
 
-        if (!endswith(p, ".service")) {
+        if (!endswith(p ?: rvalue, ".service")) {
                 log_syntax(unit, LOG_ERR, filename, line, EINVAL,
                            "Unit must be of type service, ignoring: %s", rvalue);
                 return 0;
         }
 
-        r = manager_load_unit(UNIT(s)->manager, p, NULL, &error, &x);
+        r = manager_load_unit(UNIT(s)->manager, p ?: rvalue, NULL, &error, &x);
         if (r < 0) {
-                log_syntax(unit, LOG_ERR, filename, line, EINVAL,
+                log_syntax(unit, LOG_ERR, filename, line, r,
                            "Failed to load unit %s, ignoring: %s",
                            rvalue, bus_error(&error, r));
                 dbus_error_free(&error);
@@ -1395,23 +1403,24 @@ int config_parse_service_sockets(const char *unit,
                 if (!t)
                         return log_oom();
 
-                k = unit_name_printf(UNIT(s), t);
-                if (!k)
-                        return log_oom();
+                r = unit_name_printf(UNIT(s), t, &k);
+                if (r < 0)
+                        log_syntax(unit, LOG_ERR, filename, line, -r,
+                                   "Failed to resolve specifiers, ignoring: %s", strerror(-r));
 
-                if (!endswith(k, ".socket")) {
+                if (!endswith(k ?: t, ".socket")) {
                         log_syntax(unit, LOG_ERR, filename, line, EINVAL,
-                                   "Unit must be of type socket, ignoring: %s", k);
+                                   "Unit must be of type socket, ignoring: %s", k ?: t);
                         continue;
                 }
 
-                r = unit_add_two_dependencies_by_name(UNIT(s), UNIT_WANTS, UNIT_AFTER, k, NULL, true);
+                r = unit_add_two_dependencies_by_name(UNIT(s), UNIT_WANTS, UNIT_AFTER, k ?: t, NULL, true);
                 if (r < 0)
                         log_syntax(unit, LOG_ERR, filename, line, -r,
                                    "Failed to add dependency on %s, ignoring: %s",
-                                   k, strerror(-r));
+                                   k ?: t, strerror(-r));
 
-                r = unit_add_dependency_by_name(UNIT(s), UNIT_TRIGGERED_BY, k, NULL, true);
+                r = unit_add_dependency_by_name(UNIT(s), UNIT_TRIGGERED_BY, k ?: t, NULL, true);
                 if (r < 0)
                         return r;
         }
@@ -1463,7 +1472,8 @@ int config_parse_unit_env_file(const char *unit,
 
         char ***env = data;
         Unit *u = userdata;
-        _cleanup_free_ char *s = NULL;
+        _cleanup_free_ char *n = NULL;
+        const char *s;
         int r;
 
         assert(filename);
@@ -1478,10 +1488,12 @@ int config_parse_unit_env_file(const char *unit,
                 return 0;
         }
 
-        s = unit_full_printf(u, rvalue);
-        if (!s)
-                return log_oom();
+        r = unit_full_printf(u, rvalue, &n);
+        if (r < 0)
+                log_syntax(unit, LOG_ERR, filename, line, r,
+                           "Failed to resolve specifiers, ignoring: %s", rvalue);
 
+        s = n ?: rvalue;
         if (!path_is_absolute(s[0] == '-' ? s + 1 : s)) {
                 log_syntax(unit, LOG_ERR, filename, line, EINVAL,
                            "Path '%s' is not absolute, ignoring.", s);
@@ -1509,6 +1521,7 @@ int config_parse_environ(const char *unit,
         char*** env = data, *w, *state;
         size_t l;
         _cleanup_free_ char *k = NULL;
+        int r;
 
         assert(filename);
         assert(lvalue);
@@ -1522,12 +1535,16 @@ int config_parse_environ(const char *unit,
                 return 0;
         }
 
-        if (u)
-                k = unit_full_printf(u, rvalue);
-        else
-                k = strdup(rvalue);
+        if (u) {
+                r = unit_full_printf(u, rvalue, &k);
+                if (r < 0)
+                        log_syntax(unit, LOG_ERR, filename, line, -r,
+                                   "Failed to resolve specifiers, ignoring: %s", rvalue);
+        }
 
         if (!k)
+                k = strdup(rvalue);
+        if (!k)
                 return log_oom();
 
         FOREACH_WORD_QUOTED(w, l, k, state) {
@@ -1598,6 +1615,7 @@ int config_parse_unit_condition_path(const char *unit,
         bool trigger, negate;
         Condition *c;
         _cleanup_free_ char *p = NULL;
+        int r;
 
         assert(filename);
         assert(lvalue);
@@ -1619,9 +1637,15 @@ int config_parse_unit_condition_path(const char *unit,
         if (negate)
                 rvalue++;
 
-        p = unit_full_printf(u, rvalue);
-        if (!p)
-                return log_oom();
+        r = unit_full_printf(u, rvalue, &p);
+        if (r < 0)
+                log_syntax(unit, LOG_ERR, filename, line, -r,
+                           "Failed to resolve specifiers, ignoring: %s", rvalue);
+        if (!p) {
+                p = strdup(rvalue);
+                if (!p)
+                        return log_oom();
+        }
 
         if (!path_is_absolute(p)) {
                 log_syntax(unit, LOG_ERR, filename, line, EINVAL,
@@ -1652,6 +1676,7 @@ int config_parse_unit_condition_string(const char *unit,
         bool trigger, negate;
         Condition *c;
         _cleanup_free_ char *s = NULL;
+        int r;
 
         assert(filename);
         assert(lvalue);
@@ -1673,9 +1698,15 @@ int config_parse_unit_condition_string(const char *unit,
         if (negate)
                 rvalue++;
 
-        s = unit_full_printf(u, rvalue);
-        if (!s)
-                return log_oom();
+        r = unit_full_printf(u, rvalue, &s);
+        if (r < 0)
+                log_syntax(unit, LOG_ERR, filename, line, -r,
+                           "Failed to resolve specifiers, ignoring: %s", rvalue);
+        if (!s) {
+                s = strdup(rvalue);
+                if (!s)
+                        return log_oom();
+        }
 
         c = condition_new(cond, s, trigger, negate);
         if (!c)
@@ -1929,21 +1960,26 @@ int config_parse_unit_slice(
         assert(rvalue);
         assert(u);
 
-        k = unit_name_printf(u, rvalue);
-        if (!k)
-                log_syntax(unit, LOG_ERR, filename, line, EINVAL,
+        r = unit_name_printf(u, rvalue, &k);
+        if (r < 0)
+                log_syntax(unit, LOG_ERR, filename, line, -r,
                            "Failed to resolve unit specifiers on %s. Ignoring.", rvalue);
+        if (!k) {
+                k = strdup(rvalue);
+                if (!k)
+                        return log_oom();
+        }
 
-        r = manager_load_unit(u->manager, k ? k : rvalue, NULL, NULL, &slice);
+        r = manager_load_unit(u->manager, k, NULL, NULL, &slice);
         if (r < 0) {
                 log_syntax(unit, LOG_ERR, filename, line, -r,
-                           "Failed to load slice unit %s. Ignoring.", k ? k : rvalue);
+                           "Failed to load slice unit %s. Ignoring.", k);
                 return 0;
         }
 
         if (slice->type != UNIT_SLICE) {
                 log_syntax(unit, LOG_ERR, filename, line, EINVAL,
-                           "Slice unit %s is not a slice. Ignoring.", k ? k : rvalue);
+                           "Slice unit %s is not a slice. Ignoring.", k);
                 return 0;
         }
 
diff --git a/src/core/service.c b/src/core/service.c
index 246a86e23f..cc61b546fc 100644
--- a/src/core/service.c
+++ b/src/core/service.c
@@ -1765,11 +1765,9 @@ static int service_spawn(
         } else
                 unit_unwatch_timer(UNIT(s), &s->timer_watch);
 
-        argv = unit_full_printf_strv(UNIT(s), c->argv);
-        if (!argv) {
-                r = -ENOMEM;
+        r = unit_full_printf_strv(UNIT(s), c->argv, &argv);
+        if (r < 0)
                 goto fail;
-        }
 
         our_env = new0(char*, 5);
         if (!our_env) {
diff --git a/src/core/socket.c b/src/core/socket.c
index 2130e48686..46a73e0108 100644
--- a/src/core/socket.c
+++ b/src/core/socket.c
@@ -1226,11 +1226,9 @@ static int socket_spawn(Socket *s, ExecCommand *c, pid_t *_pid) {
         if (r < 0)
                 goto fail;
 
-        argv = unit_full_printf_strv(UNIT(s), c->argv);
-        if (!argv) {
-                r = -ENOMEM;
+        r = unit_full_printf_strv(UNIT(s), c->argv, &argv);
+        if (r < 0)
                 goto fail;
-        }
 
         r = exec_spawn(c,
                        argv,
diff --git a/src/core/unit-printf.c b/src/core/unit-printf.c
index ffc203dd92..1a29a986e9 100644
--- a/src/core/unit-printf.c
+++ b/src/core/unit-printf.c
@@ -30,98 +30,158 @@
 #include "cgroup-util.h"
 #include "special.h"
 
-static char *specifier_prefix_and_instance(char specifier, void *data, void *userdata) {
+static int specifier_prefix_and_instance(char specifier, void *data, void *userdata, char **ret) {
         Unit *u = userdata;
+        char *n;
+
         assert(u);
 
-        return unit_name_to_prefix_and_instance(u->id);
+        n = unit_name_to_prefix_and_instance(u->id);
+        if (!n)
+                return -ENOMEM;
+
+        *ret = n;
+        return 0;
 }
 
-static char *specifier_prefix(char specifier, void *data, void *userdata) {
+static int specifier_prefix(char specifier, void *data, void *userdata, char **ret) {
         Unit *u = userdata;
+        char *n;
+
         assert(u);
 
-        return unit_name_to_prefix(u->id);
+        n = unit_name_to_prefix(u->id);
+        if (!n)
+                return -ENOMEM;
+
+        *ret = n;
+        return 0;
 }
 
-static char *specifier_prefix_unescaped(char specifier, void *data, void *userdata) {
+static int specifier_prefix_unescaped(char specifier, void *data, void *userdata, char **ret) {
         Unit *u = userdata;
-        char *p, *r;
+        _cleanup_free_ char *p = NULL;
+        char *n;
 
         assert(u);
 
         p = unit_name_to_prefix(u->id);
         if (!p)
-                return NULL;
+                return -ENOMEM;
 
-        r = unit_name_unescape(p);
-        free(p);
+        n = unit_name_unescape(p);
+        if (!n)
+                return -ENOMEM;
 
-        return r;
+        *ret = n;
+        return 0;
 }
 
-static char *specifier_instance_unescaped(char specifier, void *data, void *userdata) {
+static int specifier_instance_unescaped(char specifier, void *data, void *userdata, char **ret) {
         Unit *u = userdata;
+        char *n;
+
         assert(u);
 
         if (u->instance)
-                return unit_name_unescape(u->instance);
+                n = unit_name_unescape(u->instance);
+        else
+                n = strdup("");
+
+        if (!n)
+                return -ENOMEM;
 
-        return strdup("");
+        *ret = n;
+        return 0;
 }
 
-static char *specifier_filename(char specifier, void *data, void *userdata) {
+static int specifier_filename(char specifier, void *data, void *userdata, char **ret) {
         Unit *u = userdata;
+        char *n;
+
         assert(u);
 
         if (u->instance)
-                return unit_name_path_unescape(u->instance);
+                n = unit_name_path_unescape(u->instance);
+        else
+                n = unit_name_to_path(u->id);
 
-        return unit_name_to_path(u->id);
+        if (!n)
+                return -ENOMEM;
+
+        *ret = n;
+        return 0;
 }
 
-static char *specifier_cgroup(char specifier, void *data, void *userdata) {
+static int specifier_cgroup(char specifier, void *data, void *userdata, char **ret) {
         Unit *u = userdata;
+        char *n;
+
         assert(u);
 
-        return unit_default_cgroup_path(u);
+        n = unit_default_cgroup_path(u);
+        if (!n)
+                return -ENOMEM;
+
+        *ret = n;
+        return 0;
 }
 
-static char *specifier_cgroup_root(char specifier, void *data, void *userdata) {
-        _cleanup_free_ char *p = NULL;
+static int specifier_cgroup_root(char specifier, void *data, void *userdata, char **ret) {
         Unit *u = userdata;
         const char *slice;
+        char *n;
         int r;
 
         assert(u);
 
         slice = unit_slice_name(u);
         if (specifier == 'R' || !slice)
-                return strdup(u->manager->cgroup_root);
+                n = strdup(u->manager->cgroup_root);
+        else {
+                _cleanup_free_ char *p = NULL;
 
-        r = cg_slice_to_path(slice, &p);
-        if (r < 0)
-                return NULL;
+                r = cg_slice_to_path(slice, &p);
+                if (r < 0)
+                        return r;
+
+                n = strjoin(u->manager->cgroup_root, "/", p, NULL);
+                if (!n)
+                        return -ENOMEM;
+        }
 
-        return strjoin(u->manager->cgroup_root, "/", p, NULL);
+        *ret = n;
+        return 0;
 }
 
-static char *specifier_runtime(char specifier, void *data, void *userdata) {
+static int specifier_runtime(char specifier, void *data, void *userdata, char **ret) {
         Unit *u = userdata;
+        char *n = NULL;
+
         assert(u);
 
         if (u->manager->running_as == SYSTEMD_USER) {
                 const char *e;
 
                 e = getenv("XDG_RUNTIME_DIR");
-                if (e)
-                        return strdup(e);
+                if (e) {
+                        n = strdup(e);
+                        if (!n)
+                                return -ENOMEM;
+                }
         }
 
-        return strdup("/run");
+        if (!n) {
+                n = strdup("/run");
+                if (!n)
+                        return -ENOMEM;
+        }
+
+        *ret = n;
+        return 0;
 }
 
-static char *specifier_user_name(char specifier, void *data, void *userdata) {
+static int specifier_user_name(char specifier, void *data, void *userdata, char **ret) {
         Unit *u = userdata;
         ExecContext *c;
         int r;
@@ -143,26 +203,31 @@ static char *specifier_user_name(char specifier, void *data, void *userdata) {
         /* fish username from passwd */
         r = get_user_creds(&username, &uid, NULL, NULL, NULL);
         if (r < 0)
-                return NULL;
+                return r;
 
         switch (specifier) {
                 case 'U':
                         if (asprintf(&printed, "%d", uid) < 0)
-                                return NULL;
+                                return -ENOMEM;
                         break;
                 case 'u':
                         printed = strdup(username);
                         break;
         }
 
-        return printed;
+        if (!printed)
+                return -ENOMEM;
+
+        *ret = printed;
+        return 0;
 }
 
-static char *specifier_user_home(char specifier, void *data, void *userdata) {
+static int specifier_user_home(char specifier, void *data, void *userdata, char **ret) {
         Unit *u = userdata;
         ExecContext *c;
         int r;
         const char *username, *home;
+        char *n;
 
         assert(u);
 
@@ -174,25 +239,31 @@ static char *specifier_user_home(char specifier, void *data, void *userdata) {
 
                 r = get_home_dir(&h);
                 if (r < 0)
-                        return NULL;
+                        return r;
 
-                return h;
+                *ret = h;
+                return 0;
         }
 
         username = c->user;
         r = get_user_creds(&username, NULL, NULL, &home, NULL);
         if (r < 0)
-               return NULL;
+               return r;
 
-        return strdup(home);
+        n = strdup(home);
+        if (!n)
+                return -ENOMEM;
+
+        *ret = n;
+        return 0;
 }
 
-static char *specifier_user_shell(char specifier, void *data, void *userdata) {
+static int specifier_user_shell(char specifier, void *data, void *userdata, char **ret) {
         Unit *u = userdata;
         ExecContext *c;
         int r;
         const char *username, *shell;
-        char *ret;
+        char *n;
 
         assert(u);
 
@@ -205,27 +276,18 @@ static char *specifier_user_shell(char specifier, void *data, void *userdata) {
 
         /* return /bin/sh for root, otherwise the value from passwd */
         r = get_user_creds(&username, NULL, NULL, NULL, &shell);
-        if (r < 0) {
-                log_warning_unit(u->id,
-                                 "Failed to determine shell: %s",
-                                 strerror(-r));
-                return NULL;
-        }
-
-        if (!path_is_absolute(shell)) {
-                log_warning_unit(u->id,
-                                 "Shell %s is not absolute, ignoring.",
-                                 shell);
-        }
+        if (r < 0)
+                return r;
 
-        ret = strdup(shell);
-        if (!ret)
-                log_oom();
+        n = strdup(shell);
+        if (!n)
+                return -ENOMEM;
 
-        return ret;
+        *ret = n;
+        return 0;
 }
 
-char *unit_name_printf(Unit *u, const char* format) {
+int unit_name_printf(Unit *u, const char* format, char **ret) {
 
         /*
          * This will use the passed string as format string and
@@ -247,11 +309,12 @@ char *unit_name_printf(Unit *u, const char* format) {
 
         assert(u);
         assert(format);
+        assert(ret);
 
-        return specifier_printf(format, table, u);
+        return specifier_printf(format, table, u, ret);
 }
 
-char *unit_full_printf(Unit *u, const char *format) {
+int unit_full_printf(Unit *u, const char *format, char **ret) {
 
         /* This is similar to unit_name_printf() but also supports
          * unescaping. Also, adds a couple of additional codes:
@@ -296,14 +359,17 @@ char *unit_full_printf(Unit *u, const char *format) {
                 {}
         };
 
+        assert(u);
         assert(format);
+        assert(ret);
 
-        return specifier_printf(format, table, u);
+        return specifier_printf(format, table, u, ret);
 }
 
-char **unit_full_printf_strv(Unit *u, char **l) {
+int unit_full_printf_strv(Unit *u, char **l, char ***ret) {
         size_t n;
         char **r, **i, **j;
+        int q;
 
         /* Applies unit_full_printf to every entry in l */
 
@@ -312,22 +378,22 @@ char **unit_full_printf_strv(Unit *u, char **l) {
         n = strv_length(l);
         r = new(char*, n+1);
         if (!r)
-                return NULL;
+                return -ENOMEM;
 
         for (i = l, j = r; *i; i++, j++) {
-                *j = unit_full_printf(u, *i);
-                if (!*j)
+                q = unit_full_printf(u, *i, j);
+                if (q < 0)
                         goto fail;
         }
 
         *j = NULL;
-        return r;
+        *ret = r;
+        return 0;
 
 fail:
         for (j--; j >= r; j--)
                 free(*j);
 
         free(r);
-
-        return NULL;
+        return q;
 }
diff --git a/src/core/unit-printf.h b/src/core/unit-printf.h
index d2f4ccd178..51acad63e9 100644
--- a/src/core/unit-printf.h
+++ b/src/core/unit-printf.h
@@ -23,6 +23,6 @@
 
 #include "unit.h"
 
-char *unit_name_printf(Unit *u, const char* text);
-char *unit_full_printf(Unit *u, const char *text);
-char **unit_full_printf_strv(Unit *u, char **l);
+int unit_name_printf(Unit *u, const char* text, char **ret);
+int unit_full_printf(Unit *u, const char *text, char **ret);
+int unit_full_printf_strv(Unit *u, char **l, char ***ret);