diff --git a/src/core/cgroup.c b/src/core/cgroup.c
index 12f9924c17..a7ce3fceaa 100644
--- a/src/core/cgroup.c
+++ b/src/core/cgroup.c
@@ -1485,7 +1485,7 @@ static const char *migrate_callback(CGroupMask mask, void *userdata) {
         return unit_get_realized_cgroup_path(userdata, mask);
 }
 
-char *unit_default_cgroup_path(Unit *u) {
+char *unit_default_cgroup_path(const Unit *u) {
         _cleanup_free_ char *escaped = NULL, *slice = NULL;
         int r;
 
diff --git a/src/core/cgroup.h b/src/core/cgroup.h
index 6d094e9ecd..266daa20a5 100644
--- a/src/core/cgroup.h
+++ b/src/core/cgroup.h
@@ -164,7 +164,7 @@ void unit_invalidate_cgroup_members_masks(Unit *u);
 void unit_add_to_cgroup_realize_queue(Unit *u);
 
 const char *unit_get_realized_cgroup_path(Unit *u, CGroupMask mask);
-char *unit_default_cgroup_path(Unit *u);
+char *unit_default_cgroup_path(const Unit *u);
 int unit_set_cgroup_path(Unit *u, const char *path);
 int unit_pick_cgroup_path(Unit *u);
 
diff --git a/src/core/unit-printf.c b/src/core/unit-printf.c
index f57c099c39..a8e84ebe80 100644
--- a/src/core/unit-printf.c
+++ b/src/core/unit-printf.c
@@ -12,25 +12,25 @@
 #include "unit.h"
 #include "user-util.h"
 
-static int specifier_prefix_and_instance(char specifier, void *data, void *userdata, char **ret) {
-        Unit *u = userdata;
+static int specifier_prefix_and_instance(char specifier, const void *data, const void *userdata, char **ret) {
+        const Unit *u = userdata;
 
         assert(u);
 
         return unit_name_to_prefix_and_instance(u->id, ret);
 }
 
-static int specifier_prefix(char specifier, void *data, void *userdata, char **ret) {
-        Unit *u = userdata;
+static int specifier_prefix(char specifier, const void *data, const void *userdata, char **ret) {
+        const Unit *u = userdata;
 
         assert(u);
 
         return unit_name_to_prefix(u->id, ret);
 }
 
-static int specifier_prefix_unescaped(char specifier, void *data, void *userdata, char **ret) {
+static int specifier_prefix_unescaped(char specifier, const void *data, const void *userdata, char **ret) {
         _cleanup_free_ char *p = NULL;
-        Unit *u = userdata;
+        const Unit *u = userdata;
         int r;
 
         assert(u);
@@ -42,16 +42,16 @@ static int specifier_prefix_unescaped(char specifier, void *data, void *userdata
         return unit_name_unescape(p, ret);
 }
 
-static int specifier_instance_unescaped(char specifier, void *data, void *userdata, char **ret) {
-        Unit *u = userdata;
+static int specifier_instance_unescaped(char specifier, const void *data, const void *userdata, char **ret) {
+        const Unit *u = userdata;
 
         assert(u);
 
         return unit_name_unescape(strempty(u->instance), ret);
 }
 
-static int specifier_last_component(char specifier, void *data, void *userdata, char **ret) {
-        Unit *u = userdata;
+static int specifier_last_component(char specifier, const void *data, const void *userdata, char **ret) {
+        const Unit *u = userdata;
         _cleanup_free_ char *prefix = NULL;
         char *dash;
         int r;
@@ -70,7 +70,7 @@ static int specifier_last_component(char specifier, void *data, void *userdata,
         return 0;
 }
 
-static int specifier_last_component_unescaped(char specifier, void *data, void *userdata, char **ret) {
+static int specifier_last_component_unescaped(char specifier, const void *data, const void *userdata, char **ret) {
         _cleanup_free_ char *p = NULL;
         int r;
 
@@ -81,8 +81,8 @@ static int specifier_last_component_unescaped(char specifier, void *data, void *
         return unit_name_unescape(p, ret);
 }
 
-static int specifier_filename(char specifier, void *data, void *userdata, char **ret) {
-        Unit *u = userdata;
+static int specifier_filename(char specifier, const void *data, const void *userdata, char **ret) {
+        const Unit *u = userdata;
 
         assert(u);
 
@@ -92,12 +92,12 @@ static int specifier_filename(char specifier, void *data, void *userdata, char *
                 return unit_name_to_path(u->id, ret);
 }
 
-static void bad_specifier(Unit *u, char specifier) {
+static void bad_specifier(const Unit *u, char specifier) {
         log_unit_warning(u, "Specifier '%%%c' used in unit configuration, which is deprecated. Please update your unit file, as it does not work as intended.", specifier);
 }
 
-static int specifier_cgroup(char specifier, void *data, void *userdata, char **ret) {
-        Unit *u = userdata;
+static int specifier_cgroup(char specifier, const void *data, const void *userdata, char **ret) {
+        const Unit *u = userdata;
         char *n;
 
         assert(u);
@@ -115,8 +115,8 @@ static int specifier_cgroup(char specifier, void *data, void *userdata, char **r
         return 0;
 }
 
-static int specifier_cgroup_root(char specifier, void *data, void *userdata, char **ret) {
-        Unit *u = userdata;
+static int specifier_cgroup_root(char specifier, const void *data, const void *userdata, char **ret) {
+        const Unit *u = userdata;
         char *n;
 
         assert(u);
@@ -131,8 +131,8 @@ static int specifier_cgroup_root(char specifier, void *data, void *userdata, cha
         return 0;
 }
 
-static int specifier_cgroup_slice(char specifier, void *data, void *userdata, char **ret) {
-        Unit *u = userdata;
+static int specifier_cgroup_slice(char specifier, const void *data, const void *userdata, char **ret) {
+        const Unit *u = userdata;
         char *n;
 
         assert(u);
@@ -140,7 +140,7 @@ static int specifier_cgroup_slice(char specifier, void *data, void *userdata, ch
         bad_specifier(u, specifier);
 
         if (UNIT_ISSET(u->slice)) {
-                Unit *slice;
+                const Unit *slice;
 
                 slice = UNIT_DEREF(u->slice);
 
@@ -157,8 +157,8 @@ static int specifier_cgroup_slice(char specifier, void *data, void *userdata, ch
         return 0;
 }
 
-static int specifier_special_directory(char specifier, void *data, void *userdata, char **ret) {
-        Unit *u = userdata;
+static int specifier_special_directory(char specifier, const void *data, const void *userdata, char **ret) {
+        const Unit *u = userdata;
         char *n = NULL;
 
         assert(u);
diff --git a/src/core/unit.c b/src/core/unit.c
index 35ade55f23..24b14fbcd6 100644
--- a/src/core/unit.c
+++ b/src/core/unit.c
@@ -132,7 +132,7 @@ int unit_new_for_name(Manager *m, size_t size, const char *name, Unit **ret) {
         return r;
 }
 
-bool unit_has_name(Unit *u, const char *name) {
+bool unit_has_name(const Unit *u, const char *name) {
         assert(u);
         assert(name);
 
diff --git a/src/core/unit.h b/src/core/unit.h
index 312742f11b..6fd39eaca3 100644
--- a/src/core/unit.h
+++ b/src/core/unit.h
@@ -648,7 +648,7 @@ int unit_set_default_slice(Unit *u);
 
 const char *unit_description(Unit *u) _pure_;
 
-bool unit_has_name(Unit *u, const char *name);
+bool unit_has_name(const Unit *u, const char *name);
 
 UnitActiveState unit_active_state(Unit *u);
 
diff --git a/src/resolve/resolved-dnssd.c b/src/resolve/resolved-dnssd.c
index 2c28ec227a..b8e6a7abe1 100644
--- a/src/resolve/resolved-dnssd.c
+++ b/src/resolve/resolved-dnssd.c
@@ -141,7 +141,7 @@ static int dnssd_service_load(Manager *manager, const char *filename) {
         return 0;
 }
 
-static int specifier_dnssd_host_name(char specifier, void *data, void *userdata, char **ret) {
+static int specifier_dnssd_host_name(char specifier, const void *data, const void *userdata, char **ret) {
         DnssdService *s  = (DnssdService *) userdata;
         char *n;
 
diff --git a/src/shared/install-printf.c b/src/shared/install-printf.c
index b87d6b9d55..d2143beda3 100644
--- a/src/shared/install-printf.c
+++ b/src/shared/install-printf.c
@@ -14,7 +14,7 @@
 #include "unit-name.h"
 #include "user-util.h"
 
-static int specifier_prefix_and_instance(char specifier, void *data, void *userdata, char **ret) {
+static int specifier_prefix_and_instance(char specifier, const void *data, const void *userdata, char **ret) {
         const UnitFileInstallInfo *i = userdata;
         _cleanup_free_ char *prefix = NULL;
         int r;
@@ -38,7 +38,7 @@ static int specifier_prefix_and_instance(char specifier, void *data, void *userd
         return 0;
 }
 
-static int specifier_name(char specifier, void *data, void *userdata, char **ret) {
+static int specifier_name(char specifier, const void *data, const void *userdata, char **ret) {
         const UnitFileInstallInfo *i = userdata;
         char *ans;
 
@@ -54,7 +54,7 @@ static int specifier_name(char specifier, void *data, void *userdata, char **ret
         return 0;
 }
 
-static int specifier_prefix(char specifier, void *data, void *userdata, char **ret) {
+static int specifier_prefix(char specifier, const void *data, const void *userdata, char **ret) {
         const UnitFileInstallInfo *i = userdata;
 
         assert(i);
@@ -62,7 +62,7 @@ static int specifier_prefix(char specifier, void *data, void *userdata, char **r
         return unit_name_to_prefix(i->name, ret);
 }
 
-static int specifier_instance(char specifier, void *data, void *userdata, char **ret) {
+static int specifier_instance(char specifier, const void *data, const void *userdata, char **ret) {
         const UnitFileInstallInfo *i = userdata;
         char *instance;
         int r;
@@ -83,7 +83,7 @@ static int specifier_instance(char specifier, void *data, void *userdata, char *
         return 0;
 }
 
-static int specifier_last_component(char specifier, void *data, void *userdata, char **ret) {
+static int specifier_last_component(char specifier, const void *data, const void *userdata, char **ret) {
         _cleanup_free_ char *prefix = NULL;
         char *dash;
         int r;
@@ -104,8 +104,7 @@ static int specifier_last_component(char specifier, void *data, void *userdata,
         return 0;
 }
 
-int install_full_printf(UnitFileInstallInfo *i, const char *format, char **ret) {
-
+int install_full_printf(const UnitFileInstallInfo *i, const char *format, char **ret) {
         /* This is similar to unit_full_printf() but does not support
          * anything path-related.
          *
diff --git a/src/shared/install-printf.h b/src/shared/install-printf.h
index 378b3bfd92..fa8ea7ef81 100644
--- a/src/shared/install-printf.h
+++ b/src/shared/install-printf.h
@@ -3,4 +3,4 @@
 
 #include "install.h"
 
-int install_full_printf(UnitFileInstallInfo *i, const char *format, char **ret);
+int install_full_printf(const UnitFileInstallInfo *i, const char *format, char **ret);
diff --git a/src/shared/install.c b/src/shared/install.c
index 9e3d9a63b4..3104043af6 100644
--- a/src/shared/install.c
+++ b/src/shared/install.c
@@ -68,7 +68,7 @@ typedef struct {
         size_t n_rules;
 } Presets;
 
-static inline bool unit_file_install_info_has_rules(UnitFileInstallInfo *i) {
+static inline bool unit_file_install_info_has_rules(const UnitFileInstallInfo *i) {
         assert(i);
 
         return !strv_isempty(i->aliases) ||
@@ -76,7 +76,7 @@ static inline bool unit_file_install_info_has_rules(UnitFileInstallInfo *i) {
                !strv_isempty(i->required_by);
 }
 
-static inline bool unit_file_install_info_has_also(UnitFileInstallInfo *i) {
+static inline bool unit_file_install_info_has_also(const UnitFileInstallInfo *i) {
         assert(i);
 
         return !strv_isempty(i->also);
@@ -477,8 +477,10 @@ static int create_symlink(
         if (!dirname)
                 return -ENOMEM;
 
-        if (chroot_symlinks_same(paths->root_dir, dirname, dest, old_path))
+        if (chroot_symlinks_same(paths->root_dir, dirname, dest, old_path)) {
+                log_debug("Symlink %s → %s already exists", new_path, dest);
                 return 1;
+        }
 
         if (!force) {
                 unit_file_changes_add(changes, n_changes, -EEXIST, new_path, dest);
@@ -711,8 +713,9 @@ static int is_symlink_with_known_name(const UnitFileInstallInfo *i, const char *
 
 static int find_symlinks_fd(
                 const char *root_dir,
-                UnitFileInstallInfo *i,
+                const UnitFileInstallInfo *i,
                 bool match_aliases,
+                bool ignore_same_name,
                 int fd,
                 const char *path,
                 const char *config_path,
@@ -759,7 +762,7 @@ static int find_symlinks_fd(
                         }
 
                         /* This will close nfd, regardless whether it succeeds or not */
-                        q = find_symlinks_fd(root_dir, i, match_aliases, nfd,
+                        q = find_symlinks_fd(root_dir, i, match_aliases, ignore_same_name, nfd,
                                              p, config_path, same_name_link);
                         if (q > 0)
                                 return 1;
@@ -768,7 +771,7 @@ static int find_symlinks_fd(
 
                 } else if (de->d_type == DT_LNK) {
                         _cleanup_free_ char *p = NULL, *dest = NULL;
-                        bool found_path, found_dest, b = false;
+                        bool found_path = false, found_dest, b = false;
                         int q;
 
                         /* Acquire symlink name */
@@ -794,23 +797,20 @@ static int find_symlinks_fd(
                                 if (!x)
                                         return -ENOMEM;
 
-                                free(dest);
-                                dest = x;
+                                free_and_replace(dest, x);
                         }
 
-                        /* Check if the symlink itself matches what we
-                         * are looking for */
-                        if (path_is_absolute(i->name))
-                                found_path = path_equal(p, i->name);
-                        else
-                                found_path = streq(de->d_name, i->name);
+                        assert(unit_name_is_valid(i->name, UNIT_NAME_ANY));
+                        if (!ignore_same_name)
+                                /* Check if the symlink itself matches what we are looking for.
+                                 *
+                                 * If ignore_same_name is specified, we are in one of the directories which
+                                 * have lower priority than the unit file, and even if a file or symlink with
+                                 * this name was found, we should ignore it. */
+                                 found_path = streq(de->d_name, i->name);
 
-                        /* Check if what the symlink points to
-                         * matches what we are looking for */
-                        if (path_is_absolute(i->name))
-                                found_dest = path_equal(dest, i->name);
-                        else
-                                found_dest = streq(basename(dest), i->name);
+                        /* Check if what the symlink points to matches what we are looking for */
+                        found_dest = streq(basename(dest), i->name);
 
                         if (found_path && found_dest) {
                                 _cleanup_free_ char *t = NULL;
@@ -845,8 +845,9 @@ static int find_symlinks_fd(
 
 static int find_symlinks(
                 const char *root_dir,
-                UnitFileInstallInfo *i,
+                const UnitFileInstallInfo *i,
                 bool match_name,
+                bool ignore_same_name,
                 const char *config_path,
                 bool *same_name_link) {
 
@@ -864,29 +865,34 @@ static int find_symlinks(
         }
 
         /* This takes possession of fd and closes it */
-        return find_symlinks_fd(root_dir, i, match_name, fd,
+        return find_symlinks_fd(root_dir, i, match_name, ignore_same_name, fd,
                                 config_path, config_path, same_name_link);
 }
 
 static int find_symlinks_in_scope(
                 UnitFileScope scope,
                 const LookupPaths *paths,
-                UnitFileInstallInfo *i,
+                const UnitFileInstallInfo *i,
                 bool match_name,
                 UnitFileState *state) {
 
         bool same_name_link_runtime = false, same_name_link_config = false;
         bool enabled_in_runtime = false, enabled_at_all = false;
+        bool ignore_same_name = false;
         char **p;
         int r;
 
         assert(paths);
         assert(i);
 
+        /* As we iterate over the list of search paths in paths->search_path, we may encounter "same name"
+         * symlinks. The ones which are "below" (i.e. have lower priority) than the unit file itself are
+         * efectively masked, so we should ignore them. */
+
         STRV_FOREACH(p, paths->search_path)  {
                 bool same_name_link = false;
 
-                r = find_symlinks(paths->root_dir, i, match_name, *p, &same_name_link);
+                r = find_symlinks(paths->root_dir, i, match_name, ignore_same_name, *p, &same_name_link);
                 if (r < 0)
                         return r;
                 if (r > 0) {
@@ -923,6 +929,11 @@ static int find_symlinks_in_scope(
                                         same_name_link_runtime = true;
                         }
                 }
+
+                /* Check if next iteration will be "below" the unit file (either a regular file
+                 * or a symlink), and hence should be ignored */
+                if (!ignore_same_name && path_startswith(i->path, *p))
+                        ignore_same_name = true;
         }
 
         if (enabled_in_runtime) {
@@ -987,7 +998,7 @@ static UnitFileInstallInfo *install_info_find(InstallContext *c, const char *nam
 }
 
 static int install_info_may_process(
-                UnitFileInstallInfo *i,
+                const UnitFileInstallInfo *i,
                 const LookupPaths *paths,
                 UnitFileChange **changes,
                 size_t *n_changes) {
@@ -2665,7 +2676,11 @@ int unit_file_lookup_state(
         r = install_info_discover(scope, &c, paths, name, SEARCH_LOAD|SEARCH_FOLLOW_CONFIG_SYMLINKS,
                                   &i, NULL, NULL);
         if (r < 0)
-                return r;
+                return log_debug_errno(r, "Failed to discover unit %s: %m", name);
+
+        assert(IN_SET(i->type, UNIT_FILE_TYPE_REGULAR, UNIT_FILE_TYPE_MASKED));
+        log_debug("Found unit %s at %s (%s)", name, strna(i->path),
+                  i->type == UNIT_FILE_TYPE_REGULAR ? "regular file" : "mask");
 
         /* Shortcut things, if the caller just wants to know if this unit exists. */
         if (!ret)
diff --git a/src/shared/specifier.c b/src/shared/specifier.c
index 78dda05b48..b8f7537f7a 100644
--- a/src/shared/specifier.c
+++ b/src/shared/specifier.c
@@ -27,7 +27,7 @@
  * and "%" used for escaping. */
 #define POSSIBLE_SPECIFIERS ALPHANUMERICAL "%"
 
-int specifier_printf(const char *text, const Specifier table[], void *userdata, char **_ret) {
+int specifier_printf(const char *text, const Specifier table[], const void *userdata, char **_ret) {
         size_t l, allocated = 0;
         _cleanup_free_ char *ret = NULL;
         char *t;
@@ -102,7 +102,7 @@ int specifier_printf(const char *text, const Specifier table[], void *userdata,
 
 /* Generic handler for simple string replacements */
 
-int specifier_string(char specifier, void *data, void *userdata, char **ret) {
+int specifier_string(char specifier, const void *data, const void *userdata, char **ret) {
         char *n;
 
         n = strdup(strempty(data));
@@ -113,7 +113,7 @@ int specifier_string(char specifier, void *data, void *userdata, char **ret) {
         return 0;
 }
 
-int specifier_machine_id(char specifier, void *data, void *userdata, char **ret) {
+int specifier_machine_id(char specifier, const void *data, const void *userdata, char **ret) {
         sd_id128_t id;
         char *n;
         int r;
@@ -130,7 +130,7 @@ int specifier_machine_id(char specifier, void *data, void *userdata, char **ret)
         return 0;
 }
 
-int specifier_boot_id(char specifier, void *data, void *userdata, char **ret) {
+int specifier_boot_id(char specifier, const void *data, const void *userdata, char **ret) {
         sd_id128_t id;
         char *n;
         int r;
@@ -147,7 +147,7 @@ int specifier_boot_id(char specifier, void *data, void *userdata, char **ret) {
         return 0;
 }
 
-int specifier_host_name(char specifier, void *data, void *userdata, char **ret) {
+int specifier_host_name(char specifier, const void *data, const void *userdata, char **ret) {
         char *n;
 
         n = gethostname_malloc();
@@ -158,7 +158,7 @@ int specifier_host_name(char specifier, void *data, void *userdata, char **ret)
         return 0;
 }
 
-int specifier_kernel_release(char specifier, void *data, void *userdata, char **ret) {
+int specifier_kernel_release(char specifier, const void *data, const void *userdata, char **ret) {
         struct utsname uts;
         char *n;
         int r;
@@ -175,7 +175,7 @@ int specifier_kernel_release(char specifier, void *data, void *userdata, char **
         return 0;
 }
 
-int specifier_group_name(char specifier, void *data, void *userdata, char **ret) {
+int specifier_group_name(char specifier, const void *data, const void *userdata, char **ret) {
         char *t;
 
         t = gid_to_name(getgid());
@@ -186,14 +186,14 @@ int specifier_group_name(char specifier, void *data, void *userdata, char **ret)
         return 0;
 }
 
-int specifier_group_id(char specifier, void *data, void *userdata, char **ret) {
+int specifier_group_id(char specifier, const void *data, const void *userdata, char **ret) {
         if (asprintf(ret, UID_FMT, getgid()) < 0)
                 return -ENOMEM;
 
         return 0;
 }
 
-int specifier_user_name(char specifier, void *data, void *userdata, char **ret) {
+int specifier_user_name(char specifier, const void *data, const void *userdata, char **ret) {
         char *t;
 
         /* If we are UID 0 (root), this will not result in NSS, otherwise it might. This is good, as we want to be able
@@ -211,7 +211,7 @@ int specifier_user_name(char specifier, void *data, void *userdata, char **ret)
         return 0;
 }
 
-int specifier_user_id(char specifier, void *data, void *userdata, char **ret) {
+int specifier_user_id(char specifier, const void *data, const void *userdata, char **ret) {
 
         if (asprintf(ret, UID_FMT, getuid()) < 0)
                 return -ENOMEM;
@@ -219,7 +219,7 @@ int specifier_user_id(char specifier, void *data, void *userdata, char **ret) {
         return 0;
 }
 
-int specifier_user_home(char specifier, void *data, void *userdata, char **ret) {
+int specifier_user_home(char specifier, const void *data, const void *userdata, char **ret) {
 
         /* On PID 1 (which runs as root) this will not result in NSS,
          * which is good. See above */
@@ -227,7 +227,7 @@ int specifier_user_home(char specifier, void *data, void *userdata, char **ret)
         return get_home_dir(ret);
 }
 
-int specifier_user_shell(char specifier, void *data, void *userdata, char **ret) {
+int specifier_user_shell(char specifier, const void *data, const void *userdata, char **ret) {
 
         /* On PID 1 (which runs as root) this will not result in NSS,
          * which is good. See above */
@@ -235,7 +235,7 @@ int specifier_user_shell(char specifier, void *data, void *userdata, char **ret)
         return get_shell(ret);
 }
 
-int specifier_tmp_dir(char specifier, void *data, void *userdata, char **ret) {
+int specifier_tmp_dir(char specifier, const void *data, const void *userdata, char **ret) {
         const char *p;
         char *copy;
         int r;
@@ -252,7 +252,7 @@ int specifier_tmp_dir(char specifier, void *data, void *userdata, char **ret) {
         return 0;
 }
 
-int specifier_var_tmp_dir(char specifier, void *data, void *userdata, char **ret) {
+int specifier_var_tmp_dir(char specifier, const void *data, const void *userdata, char **ret) {
         const char *p;
         char *copy;
         int r;
diff --git a/src/shared/specifier.h b/src/shared/specifier.h
index 722200b998..d0221ef714 100644
--- a/src/shared/specifier.h
+++ b/src/shared/specifier.h
@@ -3,32 +3,32 @@
 
 #include "string-util.h"
 
-typedef int (*SpecifierCallback)(char specifier, void *data, void *userdata, char **ret);
+typedef int (*SpecifierCallback)(char specifier, const void *data, const void *userdata, char **ret);
 
 typedef struct Specifier {
         const char specifier;
         const SpecifierCallback lookup;
-        void *data;
+        const void *data;
 } Specifier;
 
-int specifier_printf(const char *text, const Specifier table[], void *userdata, char **ret);
+int specifier_printf(const char *text, const Specifier table[], const void *userdata, char **ret);
 
-int specifier_string(char specifier, void *data, void *userdata, char **ret);
+int specifier_string(char specifier, const void *data, const void *userdata, char **ret);
 
-int specifier_machine_id(char specifier, void *data, void *userdata, char **ret);
-int specifier_boot_id(char specifier, void *data, void *userdata, char **ret);
-int specifier_host_name(char specifier, void *data, void *userdata, char **ret);
-int specifier_kernel_release(char specifier, void *data, void *userdata, char **ret);
+int specifier_machine_id(char specifier, const void *data, const void *userdata, char **ret);
+int specifier_boot_id(char specifier, const void *data, const void *userdata, char **ret);
+int specifier_host_name(char specifier, const void *data, const void *userdata, char **ret);
+int specifier_kernel_release(char specifier, const void *data, const void *userdata, char **ret);
 
-int specifier_group_name(char specifier, void *data, void *userdata, char **ret);
-int specifier_group_id(char specifier, void *data, void *userdata, char **ret);
-int specifier_user_name(char specifier, void *data, void *userdata, char **ret);
-int specifier_user_id(char specifier, void *data, void *userdata, char **ret);
-int specifier_user_home(char specifier, void *data, void *userdata, char **ret);
-int specifier_user_shell(char specifier, void *data, void *userdata, char **ret);
+int specifier_group_name(char specifier, const void *data, const void *userdata, char **ret);
+int specifier_group_id(char specifier, const void *data, const void *userdata, char **ret);
+int specifier_user_name(char specifier, const void *data, const void *userdata, char **ret);
+int specifier_user_id(char specifier, const void *data, const void *userdata, char **ret);
+int specifier_user_home(char specifier, const void *data, const void *userdata, char **ret);
+int specifier_user_shell(char specifier, const void *data, const void *userdata, char **ret);
 
-int specifier_tmp_dir(char specifier, void *data, void *userdata, char **ret);
-int specifier_var_tmp_dir(char specifier, void *data, void *userdata, char **ret);
+int specifier_tmp_dir(char specifier, const void *data, const void *userdata, char **ret);
+int specifier_var_tmp_dir(char specifier, const void *data, const void *userdata, char **ret);
 
 static inline char* specifier_escape(const char *string) {
         return strreplace(string, "%", "%%");
diff --git a/src/tmpfiles/tmpfiles.c b/src/tmpfiles/tmpfiles.c
index 08c57a3fb1..19225f8cfd 100644
--- a/src/tmpfiles/tmpfiles.c
+++ b/src/tmpfiles/tmpfiles.c
@@ -180,8 +180,8 @@ STATIC_DESTRUCTOR_REGISTER(arg_include_prefixes, freep);
 STATIC_DESTRUCTOR_REGISTER(arg_exclude_prefixes, freep);
 STATIC_DESTRUCTOR_REGISTER(arg_root, freep);
 
-static int specifier_machine_id_safe(char specifier, void *data, void *userdata, char **ret);
-static int specifier_directory(char specifier, void *data, void *userdata, char **ret);
+static int specifier_machine_id_safe(char specifier, const void *data, const void *userdata, char **ret);
+static int specifier_directory(char specifier, const void *data, const void *userdata, char **ret);
 
 static const Specifier specifier_table[] = {
         { 'm', specifier_machine_id_safe, NULL },
@@ -204,7 +204,7 @@ static const Specifier specifier_table[] = {
         {}
 };
 
-static int specifier_machine_id_safe(char specifier, void *data, void *userdata, char **ret) {
+static int specifier_machine_id_safe(char specifier, const void *data, const void *userdata, char **ret) {
         int r;
 
         /* If /etc/machine_id is missing or empty (e.g. in a chroot environment)
@@ -218,7 +218,7 @@ static int specifier_machine_id_safe(char specifier, void *data, void *userdata,
         return r;
 }
 
-static int specifier_directory(char specifier, void *data, void *userdata, char **ret) {
+static int specifier_directory(char specifier, const void *data, const void *userdata, char **ret) {
         struct table_entry {
                 uint64_t type;
                 const char *suffix;