Adding upstream version 241.upstream/241upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3383 insertions, 0 deletions

diff --git a/src/shared/install.c b/src/shared/install.c
new file mode 100644
index 0000000..8629304
--- /dev/null
+++ b/src/shared/install.c
@@ -0,0 +1,3383 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <fnmatch.h>
+#include <limits.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#include "alloc-util.h"
+#include "conf-files.h"
+#include "conf-parser.h"
+#include "dirent-util.h"
+#include "extract-word.h"
+#include "fd-util.h"
+#include "fileio.h"
+#include "fs-util.h"
+#include "hashmap.h"
+#include "install-printf.h"
+#include "install.h"
+#include "locale-util.h"
+#include "log.h"
+#include "macro.h"
+#include "mkdir.h"
+#include "path-lookup.h"
+#include "path-util.h"
+#include "rm-rf.h"
+#include "set.h"
+#include "special.h"
+#include "stat-util.h"
+#include "string-table.h"
+#include "string-util.h"
+#include "strv.h"
+#include "unit-name.h"
+
+#define UNIT_FILE_FOLLOW_SYMLINK_MAX 64
+
+typedef enum SearchFlags {
+        SEARCH_LOAD                   = 1 << 0,
+        SEARCH_FOLLOW_CONFIG_SYMLINKS = 1 << 1,
+        SEARCH_DROPIN                 = 1 << 2,
+} SearchFlags;
+
+typedef struct {
+        OrderedHashmap *will_process;
+        OrderedHashmap *have_processed;
+} InstallContext;
+
+typedef enum {
+        PRESET_UNKNOWN,
+        PRESET_ENABLE,
+        PRESET_DISABLE,
+} PresetAction;
+
+typedef struct {
+        char *pattern;
+        PresetAction action;
+        char **instances;
+} PresetRule;
+
+typedef struct {
+        PresetRule *rules;
+        size_t n_rules;
+} Presets;
+
+static bool unit_file_install_info_has_rules(const UnitFileInstallInfo *i) {
+        assert(i);
+
+        return !strv_isempty(i->aliases) ||
+               !strv_isempty(i->wanted_by) ||
+               !strv_isempty(i->required_by);
+}
+
+static bool unit_file_install_info_has_also(const UnitFileInstallInfo *i) {
+        assert(i);
+
+        return !strv_isempty(i->also);
+}
+
+static void presets_freep(Presets *p) {
+        size_t i;
+
+        if (!p)
+                return;
+
+        for (i = 0; i < p->n_rules; i++) {
+                free(p->rules[i].pattern);
+                strv_free(p->rules[i].instances);
+        }
+
+        free(p->rules);
+        p->n_rules = 0;
+}
+
+bool unit_type_may_alias(UnitType type) {
+        return IN_SET(type,
+                      UNIT_SERVICE,
+                      UNIT_SOCKET,
+                      UNIT_TARGET,
+                      UNIT_DEVICE,
+                      UNIT_TIMER,
+                      UNIT_PATH);
+}
+
+bool unit_type_may_template(UnitType type) {
+        return IN_SET(type,
+                      UNIT_SERVICE,
+                      UNIT_SOCKET,
+                      UNIT_TARGET,
+                      UNIT_TIMER,
+                      UNIT_PATH);
+}
+
+static const char *unit_file_type_table[_UNIT_FILE_TYPE_MAX] = {
+        [UNIT_FILE_TYPE_REGULAR] = "regular",
+        [UNIT_FILE_TYPE_SYMLINK] = "symlink",
+        [UNIT_FILE_TYPE_MASKED] = "masked",
+};
+
+DEFINE_PRIVATE_STRING_TABLE_LOOKUP_TO_STRING(unit_file_type, UnitFileType);
+
+static int in_search_path(const LookupPaths *p, const char *path) {
+        _cleanup_free_ char *parent = NULL;
+        char **i;
+
+        assert(path);
+
+        parent = dirname_malloc(path);
+        if (!parent)
+                return -ENOMEM;
+
+        STRV_FOREACH(i, p->search_path)
+                if (path_equal(parent, *i))
+                        return true;
+
+        return false;
+}
+
+static const char* skip_root(const LookupPaths *p, const char *path) {
+        char *e;
+
+        assert(p);
+        assert(path);
+
+        if (!p->root_dir)
+                return path;
+
+        e = path_startswith(path, p->root_dir);
+        if (!e)
+                return NULL;
+
+        /* Make sure the returned path starts with a slash */
+        if (e[0] != '/') {
+                if (e == path || e[-1] != '/')
+                        return NULL;
+
+                e--;
+        }
+
+        return e;
+}
+
+static int path_is_generator(const LookupPaths *p, const char *path) {
+        _cleanup_free_ char *parent = NULL;
+
+        assert(p);
+        assert(path);
+
+        parent = dirname_malloc(path);
+        if (!parent)
+                return -ENOMEM;
+
+        return path_equal_ptr(parent, p->generator) ||
+               path_equal_ptr(parent, p->generator_early) ||
+               path_equal_ptr(parent, p->generator_late);
+}
+
+static int path_is_transient(const LookupPaths *p, const char *path) {
+        _cleanup_free_ char *parent = NULL;
+
+        assert(p);
+        assert(path);
+
+        parent = dirname_malloc(path);
+        if (!parent)
+                return -ENOMEM;
+
+        return path_equal_ptr(parent, p->transient);
+}
+
+static int path_is_control(const LookupPaths *p, const char *path) {
+        _cleanup_free_ char *parent = NULL;
+
+        assert(p);
+        assert(path);
+
+        parent = dirname_malloc(path);
+        if (!parent)
+                return -ENOMEM;
+
+        return path_equal_ptr(parent, p->persistent_control) ||
+               path_equal_ptr(parent, p->runtime_control);
+}
+
+static int path_is_config(const LookupPaths *p, const char *path, bool check_parent) {
+        _cleanup_free_ char *parent = NULL;
+
+        assert(p);
+        assert(path);
+
+        /* Note that we do *not* have generic checks for /etc or /run in place, since with
+         * them we couldn't discern configuration from transient or generated units */
+
+        if (check_parent) {
+                parent = dirname_malloc(path);
+                if (!parent)
+                        return -ENOMEM;
+
+                path = parent;
+        }
+
+        return path_equal_ptr(path, p->persistent_config) ||
+               path_equal_ptr(path, p->runtime_config);
+}
+
+static int path_is_runtime(const LookupPaths *p, const char *path, bool check_parent) {
+        _cleanup_free_ char *parent = NULL;
+        const char *rpath;
+
+        assert(p);
+        assert(path);
+
+        /* Everything in /run is considered runtime. On top of that we also add
+         * explicit checks for the various runtime directories, as safety net. */
+
+        rpath = skip_root(p, path);
+        if (rpath && path_startswith(rpath, "/run"))
+                return true;
+
+        if (check_parent) {
+                parent = dirname_malloc(path);
+                if (!parent)
+                        return -ENOMEM;
+
+                path = parent;
+        }
+
+        return path_equal_ptr(path, p->runtime_config) ||
+               path_equal_ptr(path, p->generator) ||
+               path_equal_ptr(path, p->generator_early) ||
+               path_equal_ptr(path, p->generator_late) ||
+               path_equal_ptr(path, p->transient) ||
+               path_equal_ptr(path, p->runtime_control);
+}
+
+static int path_is_vendor(const LookupPaths *p, const char *path) {
+        const char *rpath;
+
+        assert(p);
+        assert(path);
+
+        rpath = skip_root(p, path);
+        if (!rpath)
+                return 0;
+
+        if (path_startswith(rpath, "/usr"))
+                return true;
+
+#if HAVE_SPLIT_USR
+        if (path_startswith(rpath, "/lib"))
+                return true;
+#endif
+
+        return path_equal(rpath, SYSTEM_DATA_UNIT_PATH);
+}
+
+int unit_file_changes_add(
+                UnitFileChange **changes,
+                size_t *n_changes,
+                UnitFileChangeType type,
+                const char *path,
+                const char *source) {
+
+        _cleanup_free_ char *p = NULL, *s = NULL;
+        UnitFileChange *c;
+
+        assert(path);
+        assert(!changes == !n_changes);
+
+        if (!changes)
+                return 0;
+
+        c = reallocarray(*changes, *n_changes + 1, sizeof(UnitFileChange));
+        if (!c)
+                return -ENOMEM;
+        *changes = c;
+
+        p = strdup(path);
+        if (source)
+                s = strdup(source);
+
+        if (!p || (source && !s))
+                return -ENOMEM;
+
+        path_simplify(p, false);
+        if (s)
+                path_simplify(s, false);
+
+        c[*n_changes] = (UnitFileChange) { type, p, s };
+        p = s = NULL;
+        (*n_changes) ++;
+        return 0;
+}
+
+void unit_file_changes_free(UnitFileChange *changes, size_t n_changes) {
+        size_t i;
+
+        assert(changes || n_changes == 0);
+
+        for (i = 0; i < n_changes; i++) {
+                free(changes[i].path);
+                free(changes[i].source);
+        }
+
+        free(changes);
+}
+
+void unit_file_dump_changes(int r, const char *verb, const UnitFileChange *changes, size_t n_changes, bool quiet) {
+        size_t i;
+        bool logged = false;
+
+        assert(changes || n_changes == 0);
+        /* If verb is not specified, errors are not allowed! */
+        assert(verb || r >= 0);
+
+        for (i = 0; i < n_changes; i++) {
+                assert(verb || changes[i].type >= 0);
+
+                switch(changes[i].type) {
+                case UNIT_FILE_SYMLINK:
+                        if (!quiet)
+                                log_info("Created symlink %s %s %s.",
+                                         changes[i].path,
+                                         special_glyph(SPECIAL_GLYPH_ARROW),
+                                         changes[i].source);
+                        break;
+                case UNIT_FILE_UNLINK:
+                        if (!quiet)
+                                log_info("Removed %s.", changes[i].path);
+                        break;
+                case UNIT_FILE_IS_MASKED:
+                        if (!quiet)
+                                log_info("Unit %s is masked, ignoring.", changes[i].path);
+                        break;
+                case UNIT_FILE_IS_DANGLING:
+                        if (!quiet)
+                                log_info("Unit %s is an alias to a unit that is not present, ignoring.",
+                                         changes[i].path);
+                        break;
+                case -EEXIST:
+                        if (changes[i].source)
+                                log_error_errno(changes[i].type,
+                                                "Failed to %s unit, file %s already exists and is a symlink to %s.",
+                                                verb, changes[i].path, changes[i].source);
+                        else
+                                log_error_errno(changes[i].type,
+                                                "Failed to %s unit, file %s already exists.",
+                                                verb, changes[i].path);
+                        logged = true;
+                        break;
+                case -ERFKILL:
+                        log_error_errno(changes[i].type, "Failed to %s unit, unit %s is masked.",
+                                        verb, changes[i].path);
+                        logged = true;
+                        break;
+                case -EADDRNOTAVAIL:
+                        log_error_errno(changes[i].type, "Failed to %s unit, unit %s is transient or generated.",
+                                        verb, changes[i].path);
+                        logged = true;
+                        break;
+                case -ELOOP:
+                        log_error_errno(changes[i].type, "Failed to %s unit, refusing to operate on linked unit file %s",
+                                        verb, changes[i].path);
+                        logged = true;
+                        break;
+
+                case -ENOENT:
+                        log_error_errno(changes[i].type, "Failed to %s unit, unit %s does not exist.", verb, changes[i].path);
+                        logged = true;
+                        break;
+
+                default:
+                        assert(changes[i].type < 0);
+                        log_error_errno(changes[i].type, "Failed to %s unit, file %s: %m.",
+                                        verb, changes[i].path);
+                        logged = true;
+                }
+        }
+
+        if (r < 0 && !logged)
+                log_error_errno(r, "Failed to %s: %m.", verb);
+}
+
+/**
+ * Checks if two paths or symlinks from wd are the same, when root is the root of the filesystem.
+ * wc should be the full path in the host file system.
+ */
+static bool chroot_symlinks_same(const char *root, const char *wd, const char *a, const char *b) {
+        assert(path_is_absolute(wd));
+
+        /* This will give incorrect results if the paths are relative and go outside
+         * of the chroot. False negatives are possible. */
+
+        if (!root)
+                root = "/";
+
+        a = strjoina(path_is_absolute(a) ? root : wd, "/", a);
+        b = strjoina(path_is_absolute(b) ? root : wd, "/", b);
+        return path_equal_or_files_same(a, b, 0);
+}
+
+static int create_symlink(
+                const LookupPaths *paths,
+                const char *old_path,
+                const char *new_path,
+                bool force,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+
+        _cleanup_free_ char *dest = NULL, *dirname = NULL;
+        const char *rp;
+        int r;
+
+        assert(old_path);
+        assert(new_path);
+
+        rp = skip_root(paths, old_path);
+        if (rp)
+                old_path = rp;
+
+        /* Actually create a symlink, and remember that we did. Is
+         * smart enough to check if there's already a valid symlink in
+         * place.
+         *
+         * Returns 1 if a symlink was created or already exists and points to
+         * the right place, or negative on error.
+         */
+
+        mkdir_parents_label(new_path, 0755);
+
+        if (symlink(old_path, new_path) >= 0) {
+                unit_file_changes_add(changes, n_changes, UNIT_FILE_SYMLINK, new_path, old_path);
+                return 1;
+        }
+
+        if (errno != EEXIST) {
+                unit_file_changes_add(changes, n_changes, -errno, new_path, NULL);
+                return -errno;
+        }
+
+        r = readlink_malloc(new_path, &dest);
+        if (r < 0) {
+                /* translate EINVAL (non-symlink exists) to EEXIST */
+                if (r == -EINVAL)
+                        r = -EEXIST;
+
+                unit_file_changes_add(changes, n_changes, r, new_path, NULL);
+                return r;
+        }
+
+        dirname = dirname_malloc(new_path);
+        if (!dirname)
+                return -ENOMEM;
+
+        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);
+                return -EEXIST;
+        }
+
+        r = symlink_atomic(old_path, new_path);
+        if (r < 0) {
+                unit_file_changes_add(changes, n_changes, r, new_path, NULL);
+                return r;
+        }
+
+        unit_file_changes_add(changes, n_changes, UNIT_FILE_UNLINK, new_path, NULL);
+        unit_file_changes_add(changes, n_changes, UNIT_FILE_SYMLINK, new_path, old_path);
+
+        return 1;
+}
+
+static int mark_symlink_for_removal(
+                Set **remove_symlinks_to,
+                const char *p) {
+
+        char *n;
+        int r;
+
+        assert(p);
+
+        r = set_ensure_allocated(remove_symlinks_to, &path_hash_ops);
+        if (r < 0)
+                return r;
+
+        n = strdup(p);
+        if (!n)
+                return -ENOMEM;
+
+        path_simplify(n, false);
+
+        r = set_consume(*remove_symlinks_to, n);
+        if (r == -EEXIST)
+                return 0;
+        if (r < 0)
+                return r;
+
+        return 1;
+}
+
+static int remove_marked_symlinks_fd(
+                Set *remove_symlinks_to,
+                int fd,
+                const char *path,
+                const char *config_path,
+                const LookupPaths *lp,
+                bool dry_run,
+                bool *restart,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+
+        _cleanup_closedir_ DIR *d = NULL;
+        struct dirent *de;
+        int r = 0;
+
+        assert(remove_symlinks_to);
+        assert(fd >= 0);
+        assert(path);
+        assert(config_path);
+        assert(lp);
+        assert(restart);
+
+        d = fdopendir(fd);
+        if (!d) {
+                safe_close(fd);
+                return -errno;
+        }
+
+        rewinddir(d);
+
+        FOREACH_DIRENT(de, d, return -errno) {
+
+                dirent_ensure_type(d, de);
+
+                if (de->d_type == DT_DIR) {
+                        _cleanup_free_ char *p = NULL;
+                        int nfd, q;
+
+                        nfd = openat(fd, de->d_name, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_NOFOLLOW);
+                        if (nfd < 0) {
+                                if (errno == ENOENT)
+                                        continue;
+
+                                if (r == 0)
+                                        r = -errno;
+                                continue;
+                        }
+
+                        p = path_make_absolute(de->d_name, path);
+                        if (!p) {
+                                safe_close(nfd);
+                                return -ENOMEM;
+                        }
+
+                        /* This will close nfd, regardless whether it succeeds or not */
+                        q = remove_marked_symlinks_fd(remove_symlinks_to, nfd, p, config_path, lp, dry_run, restart, changes, n_changes);
+                        if (q < 0 && r == 0)
+                                r = q;
+
+                } else if (de->d_type == DT_LNK) {
+                        _cleanup_free_ char *p = NULL, *dest = NULL;
+                        const char *rp;
+                        bool found;
+                        int q;
+
+                        if (!unit_name_is_valid(de->d_name, UNIT_NAME_ANY))
+                                continue;
+
+                        p = path_make_absolute(de->d_name, path);
+                        if (!p)
+                                return -ENOMEM;
+                        path_simplify(p, false);
+
+                        q = readlink_malloc(p, &dest);
+                        if (q == -ENOENT)
+                                continue;
+                        if (q < 0) {
+                                if (r == 0)
+                                        r = q;
+                                continue;
+                        }
+
+                        /* We remove all links pointing to a file or path that is marked, as well as all files sharing
+                         * the same name as a file that is marked. */
+
+                        found = set_contains(remove_symlinks_to, dest) ||
+                                set_contains(remove_symlinks_to, basename(dest)) ||
+                                set_contains(remove_symlinks_to, de->d_name);
+
+                        if (!found)
+                                continue;
+
+                        if (!dry_run) {
+                                if (unlinkat(fd, de->d_name, 0) < 0 && errno != ENOENT) {
+                                        if (r == 0)
+                                                r = -errno;
+                                        unit_file_changes_add(changes, n_changes, -errno, p, NULL);
+                                        continue;
+                                }
+
+                                (void) rmdir_parents(p, config_path);
+                        }
+
+                        unit_file_changes_add(changes, n_changes, UNIT_FILE_UNLINK, p, NULL);
+
+                        /* Now, remember the full path (but with the root prefix removed) of
+                         * the symlink we just removed, and remove any symlinks to it, too. */
+
+                        rp = skip_root(lp, p);
+                        q = mark_symlink_for_removal(&remove_symlinks_to, rp ?: p);
+                        if (q < 0)
+                                return q;
+                        if (q > 0 && !dry_run)
+                                *restart = true;
+                }
+        }
+
+        return r;
+}
+
+static int remove_marked_symlinks(
+                Set *remove_symlinks_to,
+                const char *config_path,
+                const LookupPaths *lp,
+                bool dry_run,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+
+        _cleanup_close_ int fd = -1;
+        bool restart;
+        int r = 0;
+
+        assert(config_path);
+        assert(lp);
+
+        if (set_size(remove_symlinks_to) <= 0)
+                return 0;
+
+        fd = open(config_path, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC);
+        if (fd < 0)
+                return errno == ENOENT ? 0 : -errno;
+
+        do {
+                int q, cfd;
+                restart = false;
+
+                cfd = fcntl(fd, F_DUPFD_CLOEXEC, 3);
+                if (cfd < 0)
+                        return -errno;
+
+                /* This takes possession of cfd and closes it */
+                q = remove_marked_symlinks_fd(remove_symlinks_to, cfd, config_path, config_path, lp, dry_run, &restart, changes, n_changes);
+                if (r == 0)
+                        r = q;
+        } while (restart);
+
+        return r;
+}
+
+static int is_symlink_with_known_name(const UnitFileInstallInfo *i, const char *name) {
+        int r;
+
+        if (streq(name, i->name))
+                return true;
+
+        if (strv_contains(i->aliases, name))
+                return true;
+
+        /* Look for template symlink matching DefaultInstance */
+        if (i->default_instance && unit_name_is_valid(i->name, UNIT_NAME_TEMPLATE)) {
+                _cleanup_free_ char *s = NULL;
+
+                r = unit_name_replace_instance(i->name, i->default_instance, &s);
+                if (r < 0) {
+                        if (r != -EINVAL)
+                                return r;
+
+                } else if (streq(name, s))
+                        return true;
+        }
+
+        return false;
+}
+
+static int find_symlinks_fd(
+                const char *root_dir,
+                const UnitFileInstallInfo *i,
+                bool match_aliases,
+                bool ignore_same_name,
+                int fd,
+                const char *path,
+                const char *config_path,
+                bool *same_name_link) {
+
+        _cleanup_closedir_ DIR *d = NULL;
+        struct dirent *de;
+        int r = 0;
+
+        assert(i);
+        assert(fd >= 0);
+        assert(path);
+        assert(config_path);
+        assert(same_name_link);
+
+        d = fdopendir(fd);
+        if (!d) {
+                safe_close(fd);
+                return -errno;
+        }
+
+        FOREACH_DIRENT(de, d, return -errno) {
+
+                dirent_ensure_type(d, de);
+
+                if (de->d_type == DT_DIR) {
+                        _cleanup_free_ char *p = NULL;
+                        int nfd, q;
+
+                        nfd = openat(fd, de->d_name, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_NOFOLLOW);
+                        if (nfd < 0) {
+                                if (errno == ENOENT)
+                                        continue;
+
+                                if (r == 0)
+                                        r = -errno;
+                                continue;
+                        }
+
+                        p = path_make_absolute(de->d_name, path);
+                        if (!p) {
+                                safe_close(nfd);
+                                return -ENOMEM;
+                        }
+
+                        /* This will close nfd, regardless whether it succeeds or not */
+                        q = find_symlinks_fd(root_dir, i, match_aliases, ignore_same_name, nfd,
+                                             p, config_path, same_name_link);
+                        if (q > 0)
+                                return 1;
+                        if (r == 0)
+                                r = q;
+
+                } else if (de->d_type == DT_LNK) {
+                        _cleanup_free_ char *p = NULL, *dest = NULL;
+                        bool found_path = false, found_dest, b = false;
+                        int q;
+
+                        /* Acquire symlink name */
+                        p = path_make_absolute(de->d_name, path);
+                        if (!p)
+                                return -ENOMEM;
+
+                        /* Acquire symlink destination */
+                        q = readlink_malloc(p, &dest);
+                        if (q == -ENOENT)
+                                continue;
+                        if (q < 0) {
+                                if (r == 0)
+                                        r = q;
+                                continue;
+                        }
+
+                        /* Make absolute */
+                        if (!path_is_absolute(dest)) {
+                                char *x;
+
+                                x = prefix_root(root_dir, dest);
+                                if (!x)
+                                        return -ENOMEM;
+
+                                free_and_replace(dest, x);
+                        }
+
+                        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 */
+                        found_dest = streq(basename(dest), i->name);
+
+                        if (found_path && found_dest) {
+                                _cleanup_free_ char *t = NULL;
+
+                                /* Filter out same name links in the main
+                                 * config path */
+                                t = path_make_absolute(i->name, config_path);
+                                if (!t)
+                                        return -ENOMEM;
+
+                                b = path_equal(t, p);
+                        }
+
+                        if (b)
+                                *same_name_link = true;
+                        else if (found_path || found_dest) {
+                                if (!match_aliases)
+                                        return 1;
+
+                                /* Check if symlink name is in the set of names used by [Install] */
+                                q = is_symlink_with_known_name(i, de->d_name);
+                                if (q < 0)
+                                        return q;
+                                if (q > 0)
+                                        return 1;
+                        }
+                }
+        }
+
+        return r;
+}
+
+static int find_symlinks(
+                const char *root_dir,
+                const UnitFileInstallInfo *i,
+                bool match_name,
+                bool ignore_same_name,
+                const char *config_path,
+                bool *same_name_link) {
+
+        int fd;
+
+        assert(i);
+        assert(config_path);
+        assert(same_name_link);
+
+        fd = open(config_path, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC);
+        if (fd < 0) {
+                if (IN_SET(errno, ENOENT, ENOTDIR, EACCES))
+                        return 0;
+                return -errno;
+        }
+
+        /* This takes possession of fd and closes it */
+        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,
+                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, ignore_same_name, *p, &same_name_link);
+                if (r < 0)
+                        return r;
+                if (r > 0) {
+                        /* We found symlinks in this dir? Yay! Let's see where precisely it is enabled. */
+
+                        if (path_equal_ptr(*p, paths->persistent_config)) {
+                                /* This is the best outcome, let's return it immediately. */
+                                *state = UNIT_FILE_ENABLED;
+                                return 1;
+                        }
+
+                        /* look for global enablement of user units */
+                        if (scope == UNIT_FILE_USER && path_is_user_config_dir(*p)) {
+                                *state = UNIT_FILE_ENABLED;
+                                return 1;
+                        }
+
+                        r = path_is_runtime(paths, *p, false);
+                        if (r < 0)
+                                return r;
+                        if (r > 0)
+                                enabled_in_runtime = true;
+                        else
+                                enabled_at_all = true;
+
+                } else if (same_name_link) {
+                        if (path_equal_ptr(*p, paths->persistent_config))
+                                same_name_link_config = true;
+                        else {
+                                r = path_is_runtime(paths, *p, false);
+                                if (r < 0)
+                                        return r;
+                                if (r > 0)
+                                        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) {
+                *state = UNIT_FILE_ENABLED_RUNTIME;
+                return 1;
+        }
+
+        /* Here's a special rule: if the unit we are looking for is an instance, and it symlinked in the search path
+         * outside of runtime and configuration directory, then we consider it statically enabled. Note we do that only
+         * for instance, not for regular names, as those are merely aliases, while instances explicitly instantiate
+         * something, and hence are a much stronger concept. */
+        if (enabled_at_all && unit_name_is_valid(i->name, UNIT_NAME_INSTANCE)) {
+                *state = UNIT_FILE_STATIC;
+                return 1;
+        }
+
+        /* Hmm, we didn't find it, but maybe we found the same name
+         * link? */
+        if (same_name_link_config) {
+                *state = UNIT_FILE_LINKED;
+                return 1;
+        }
+        if (same_name_link_runtime) {
+                *state = UNIT_FILE_LINKED_RUNTIME;
+                return 1;
+        }
+
+        return 0;
+}
+
+static void install_info_free(UnitFileInstallInfo *i) {
+
+        if (!i)
+                return;
+
+        free(i->name);
+        free(i->path);
+        strv_free(i->aliases);
+        strv_free(i->wanted_by);
+        strv_free(i->required_by);
+        strv_free(i->also);
+        free(i->default_instance);
+        free(i->symlink_target);
+        free(i);
+}
+
+static void install_context_done(InstallContext *c) {
+        assert(c);
+
+        c->will_process = ordered_hashmap_free_with_destructor(c->will_process, install_info_free);
+        c->have_processed = ordered_hashmap_free_with_destructor(c->have_processed, install_info_free);
+}
+
+static UnitFileInstallInfo *install_info_find(InstallContext *c, const char *name) {
+        UnitFileInstallInfo *i;
+
+        i = ordered_hashmap_get(c->have_processed, name);
+        if (i)
+                return i;
+
+        return ordered_hashmap_get(c->will_process, name);
+}
+
+static int install_info_may_process(
+                const UnitFileInstallInfo *i,
+                const LookupPaths *paths,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+        assert(i);
+        assert(paths);
+
+        /* Checks whether the loaded unit file is one we should process, or is masked,
+         * transient or generated and thus not subject to enable/disable operations. */
+
+        if (i->type == UNIT_FILE_TYPE_MASKED) {
+                unit_file_changes_add(changes, n_changes, -ERFKILL, i->path, NULL);
+                return -ERFKILL;
+        }
+        if (path_is_generator(paths, i->path) ||
+            path_is_transient(paths, i->path)) {
+                unit_file_changes_add(changes, n_changes, -EADDRNOTAVAIL, i->path, NULL);
+                return -EADDRNOTAVAIL;
+        }
+
+        return 0;
+}
+
+/**
+ * Adds a new UnitFileInstallInfo entry under name in the InstallContext.will_process
+ * hashmap, or retrieves the existing one if already present.
+ *
+ * Returns negative on error, 0 if the unit was already known, 1 otherwise.
+ */
+static int install_info_add(
+                InstallContext *c,
+                const char *name,
+                const char *path,
+                bool auxiliary,
+                UnitFileInstallInfo **ret) {
+
+        UnitFileInstallInfo *i = NULL;
+        int r;
+
+        assert(c);
+        assert(name || path);
+
+        if (!name)
+                name = basename(path);
+
+        if (!unit_name_is_valid(name, UNIT_NAME_ANY))
+                return -EINVAL;
+
+        i = install_info_find(c, name);
+        if (i) {
+                i->auxiliary = i->auxiliary && auxiliary;
+
+                if (ret)
+                        *ret = i;
+                return 0;
+        }
+
+        r = ordered_hashmap_ensure_allocated(&c->will_process, &string_hash_ops);
+        if (r < 0)
+                return r;
+
+        i = new(UnitFileInstallInfo, 1);
+        if (!i)
+                return -ENOMEM;
+
+        *i = (UnitFileInstallInfo) {
+                .type = _UNIT_FILE_TYPE_INVALID,
+                .auxiliary = auxiliary,
+        };
+
+        i->name = strdup(name);
+        if (!i->name) {
+                r = -ENOMEM;
+                goto fail;
+        }
+
+        if (path) {
+                i->path = strdup(path);
+                if (!i->path) {
+                        r = -ENOMEM;
+                        goto fail;
+                }
+        }
+
+        r = ordered_hashmap_put(c->will_process, i->name, i);
+        if (r < 0)
+                goto fail;
+
+        if (ret)
+                *ret = i;
+
+        return 1;
+
+fail:
+        install_info_free(i);
+        return r;
+}
+
+static int config_parse_alias(
+                const char *unit,
+                const char *filename,
+                unsigned line,
+                const char *section,
+                unsigned section_line,
+                const char *lvalue,
+                int ltype,
+                const char *rvalue,
+                void *data,
+                void *userdata) {
+
+        UnitType type;
+
+        assert(unit);
+        assert(filename);
+        assert(lvalue);
+        assert(rvalue);
+
+        type = unit_name_to_type(unit);
+        if (!unit_type_may_alias(type))
+                return log_syntax(unit, LOG_WARNING, filename, line, 0,
+                                  "Alias= is not allowed for %s units, ignoring.",
+                                  unit_type_to_string(type));
+
+        return config_parse_strv(unit, filename, line, section, section_line,
+                                 lvalue, ltype, rvalue, data, userdata);
+}
+
+static int config_parse_also(
+                const char *unit,
+                const char *filename,
+                unsigned line,
+                const char *section,
+                unsigned section_line,
+                const char *lvalue,
+                int ltype,
+                const char *rvalue,
+                void *data,
+                void *userdata) {
+
+        UnitFileInstallInfo *info = userdata, *alsoinfo = NULL;
+        InstallContext *c = data;
+        int r;
+
+        assert(unit);
+        assert(filename);
+        assert(lvalue);
+        assert(rvalue);
+
+        for (;;) {
+                _cleanup_free_ char *word = NULL, *printed = NULL;
+
+                r = extract_first_word(&rvalue, &word, NULL, 0);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        break;
+
+                r = install_full_printf(info, word, &printed);
+                if (r < 0)
+                        return r;
+
+                if (!unit_name_is_valid(printed, UNIT_NAME_ANY))
+                        return -EINVAL;
+
+                r = install_info_add(c, printed, NULL, true, &alsoinfo);
+                if (r < 0)
+                        return r;
+
+                r = strv_push(&info->also, printed);
+                if (r < 0)
+                        return r;
+
+                printed = NULL;
+        }
+
+        return 0;
+}
+
+static int config_parse_default_instance(
+                const char *unit,
+                const char *filename,
+                unsigned line,
+                const char *section,
+                unsigned section_line,
+                const char *lvalue,
+                int ltype,
+                const char *rvalue,
+                void *data,
+                void *userdata) {
+
+        UnitFileInstallInfo *i = data;
+        _cleanup_free_ char *printed = NULL;
+        int r;
+
+        assert(unit);
+        assert(filename);
+        assert(lvalue);
+        assert(rvalue);
+
+        if (unit_name_is_valid(unit, UNIT_NAME_INSTANCE))
+                /* When enabling an instance, we might be using a template unit file,
+                 * but we should ignore DefaultInstance silently. */
+                return 0;
+        if (!unit_name_is_valid(unit, UNIT_NAME_TEMPLATE))
+                return log_syntax(unit, LOG_WARNING, filename, line, 0,
+                                  "DefaultInstance= only makes sense for template units, ignoring.");
+
+        r = install_full_printf(i, rvalue, &printed);
+        if (r < 0)
+                return r;
+
+        if (!unit_instance_is_valid(printed))
+                return -EINVAL;
+
+        return free_and_replace(i->default_instance, printed);
+}
+
+static int unit_file_load(
+                InstallContext *c,
+                UnitFileInstallInfo *info,
+                const char *path,
+                const char *root_dir,
+                SearchFlags flags) {
+
+        const ConfigTableItem items[] = {
+                { "Install", "Alias",           config_parse_alias,            0, &info->aliases           },
+                { "Install", "WantedBy",        config_parse_strv,             0, &info->wanted_by         },
+                { "Install", "RequiredBy",      config_parse_strv,             0, &info->required_by       },
+                { "Install", "DefaultInstance", config_parse_default_instance, 0, info                     },
+                { "Install", "Also",            config_parse_also,             0, c                        },
+                {}
+        };
+
+        UnitType type;
+        _cleanup_fclose_ FILE *f = NULL;
+        _cleanup_close_ int fd = -1;
+        struct stat st;
+        int r;
+
+        assert(info);
+        assert(path);
+
+        if (!(flags & SEARCH_DROPIN)) {
+                /* Loading or checking for the main unit file… */
+
+                type = unit_name_to_type(info->name);
+                if (type < 0)
+                        return -EINVAL;
+                if (unit_name_is_valid(info->name, UNIT_NAME_TEMPLATE|UNIT_NAME_INSTANCE) && !unit_type_may_template(type))
+                        return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
+                                               "Unit type %s cannot be templated.", unit_type_to_string(type));
+
+                if (!(flags & SEARCH_LOAD)) {
+                        r = lstat(path, &st);
+                        if (r < 0)
+                                return -errno;
+
+                        if (null_or_empty(&st))
+                                info->type = UNIT_FILE_TYPE_MASKED;
+                        else if (S_ISREG(st.st_mode))
+                                info->type = UNIT_FILE_TYPE_REGULAR;
+                        else if (S_ISLNK(st.st_mode))
+                                return -ELOOP;
+                        else if (S_ISDIR(st.st_mode))
+                                return -EISDIR;
+                        else
+                                return -ENOTTY;
+
+                        return 0;
+                }
+
+                fd = open(path, O_RDONLY|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW);
+                if (fd < 0)
+                        return -errno;
+        } else {
+                /* Operating on a drop-in file. If we aren't supposed to load the unit file drop-ins don't matter, let's hence shortcut this. */
+
+                if (!(flags & SEARCH_LOAD))
+                        return 0;
+
+                fd = chase_symlinks_and_open(path, root_dir, 0, O_RDONLY|O_CLOEXEC|O_NOCTTY, NULL);
+                if (fd < 0)
+                        return fd;
+        }
+
+        if (fstat(fd, &st) < 0)
+                return -errno;
+
+        if (null_or_empty(&st)) {
+                if ((flags & SEARCH_DROPIN) == 0)
+                        info->type = UNIT_FILE_TYPE_MASKED;
+
+                return 0;
+        }
+
+        r = stat_verify_regular(&st);
+        if (r < 0)
+                return r;
+
+        f = fdopen(fd, "r");
+        if (!f)
+                return -errno;
+        fd = -1;
+
+        /* c is only needed if we actually load the file (it's referenced from items[] btw, in case you wonder.) */
+        assert(c);
+
+        r = config_parse(info->name, path, f,
+                         NULL,
+                         config_item_table_lookup, items,
+                         CONFIG_PARSE_RELAXED|CONFIG_PARSE_ALLOW_INCLUDE, info);
+        if (r < 0)
+                return log_debug_errno(r, "Failed to parse %s: %m", info->name);
+
+        if ((flags & SEARCH_DROPIN) == 0)
+                info->type = UNIT_FILE_TYPE_REGULAR;
+
+        return
+                (int) strv_length(info->aliases) +
+                (int) strv_length(info->wanted_by) +
+                (int) strv_length(info->required_by);
+}
+
+static int unit_file_load_or_readlink(
+                InstallContext *c,
+                UnitFileInstallInfo *info,
+                const char *path,
+                const char *root_dir,
+                SearchFlags flags) {
+
+        _cleanup_free_ char *target = NULL;
+        int r;
+
+        r = unit_file_load(c, info, path, root_dir, flags);
+        if (r != -ELOOP || (flags & SEARCH_DROPIN))
+                return r;
+
+        /* This is a symlink, let's read it. */
+
+        r = readlink_malloc(path, &target);
+        if (r < 0)
+                return r;
+
+        if (path_equal(target, "/dev/null"))
+                info->type = UNIT_FILE_TYPE_MASKED;
+        else {
+                const char *bn;
+                UnitType a, b;
+
+                bn = basename(target);
+
+                if (unit_name_is_valid(info->name, UNIT_NAME_PLAIN)) {
+
+                        if (!unit_name_is_valid(bn, UNIT_NAME_PLAIN))
+                                return -EINVAL;
+
+                } else if (unit_name_is_valid(info->name, UNIT_NAME_INSTANCE)) {
+
+                        if (!unit_name_is_valid(bn, UNIT_NAME_INSTANCE|UNIT_NAME_TEMPLATE))
+                                return -EINVAL;
+
+                } else if (unit_name_is_valid(info->name, UNIT_NAME_TEMPLATE)) {
+
+                        if (!unit_name_is_valid(bn, UNIT_NAME_TEMPLATE))
+                                return -EINVAL;
+                } else
+                        return -EINVAL;
+
+                /* Enforce that the symlink destination does not
+                 * change the unit file type. */
+
+                a = unit_name_to_type(info->name);
+                b = unit_name_to_type(bn);
+                if (a < 0 || b < 0 || a != b)
+                        return -EINVAL;
+
+                if (path_is_absolute(target))
+                        /* This is an absolute path, prefix the root so that we always deal with fully qualified paths */
+                        info->symlink_target = prefix_root(root_dir, target);
+                else
+                        /* This is a relative path, take it relative to the dir the symlink is located in. */
+                        info->symlink_target = file_in_same_dir(path, target);
+                if (!info->symlink_target)
+                        return -ENOMEM;
+
+                info->type = UNIT_FILE_TYPE_SYMLINK;
+        }
+
+        return 0;
+}
+
+static int unit_file_search(
+                InstallContext *c,
+                UnitFileInstallInfo *info,
+                const LookupPaths *paths,
+                SearchFlags flags) {
+
+        const char *dropin_dir_name = NULL, *dropin_template_dir_name = NULL;
+        _cleanup_strv_free_ char **dirs = NULL, **files = NULL;
+        _cleanup_free_ char *template = NULL;
+        bool found_unit = false;
+        int r, result;
+        char **p;
+
+        assert(info);
+        assert(paths);
+
+        /* Was this unit already loaded? */
+        if (info->type != _UNIT_FILE_TYPE_INVALID)
+                return 0;
+
+        if (info->path)
+                return unit_file_load_or_readlink(c, info, info->path, paths->root_dir, flags);
+
+        assert(info->name);
+
+        if (unit_name_is_valid(info->name, UNIT_NAME_INSTANCE)) {
+                r = unit_name_template(info->name, &template);
+                if (r < 0)
+                        return r;
+        }
+
+        STRV_FOREACH(p, paths->search_path) {
+                _cleanup_free_ char *path = NULL;
+
+                path = strjoin(*p, "/", info->name);
+                if (!path)
+                        return -ENOMEM;
+
+                r = unit_file_load_or_readlink(c, info, path, paths->root_dir, flags);
+                if (r >= 0) {
+                        info->path = TAKE_PTR(path);
+                        result = r;
+                        found_unit = true;
+                        break;
+                } else if (!IN_SET(r, -ENOENT, -ENOTDIR, -EACCES))
+                        return r;
+        }
+
+        if (!found_unit && template) {
+
+                /* Unit file doesn't exist, however instance
+                 * enablement was requested.  We will check if it is
+                 * possible to load template unit file. */
+
+                STRV_FOREACH(p, paths->search_path) {
+                        _cleanup_free_ char *path = NULL;
+
+                        path = strjoin(*p, "/", template);
+                        if (!path)
+                                return -ENOMEM;
+
+                        r = unit_file_load_or_readlink(c, info, path, paths->root_dir, flags);
+                        if (r >= 0) {
+                                info->path = TAKE_PTR(path);
+                                result = r;
+                                found_unit = true;
+                                break;
+                        } else if (!IN_SET(r, -ENOENT, -ENOTDIR, -EACCES))
+                                return r;
+                }
+        }
+
+        if (!found_unit)
+                return log_debug_errno(SYNTHETIC_ERRNO(ENOENT),
+                                       "Cannot find unit %s%s%s.",
+                                       info->name, template ? " or " : "", strempty(template));
+
+        if (info->type == UNIT_FILE_TYPE_MASKED)
+                return result;
+
+        /* Search for drop-in directories */
+
+        dropin_dir_name = strjoina(info->name, ".d");
+        STRV_FOREACH(p, paths->search_path) {
+                char *path;
+
+                path = path_join(*p, dropin_dir_name);
+                if (!path)
+                        return -ENOMEM;
+
+                r = strv_consume(&dirs, path);
+                if (r < 0)
+                        return r;
+        }
+
+        if (template) {
+                dropin_template_dir_name = strjoina(template, ".d");
+                STRV_FOREACH(p, paths->search_path) {
+                        char *path;
+
+                        path = path_join(*p, dropin_template_dir_name);
+                        if (!path)
+                                return -ENOMEM;
+
+                        r = strv_consume(&dirs, path);
+                        if (r < 0)
+                                return r;
+                }
+        }
+
+        /* Load drop-in conf files */
+
+        r = conf_files_list_strv(&files, ".conf", NULL, 0, (const char**) dirs);
+        if (r < 0)
+                return log_debug_errno(r, "Failed to get list of conf files: %m");
+
+        STRV_FOREACH(p, files) {
+                r = unit_file_load_or_readlink(c, info, *p, paths->root_dir, flags | SEARCH_DROPIN);
+                if (r < 0)
+                        return log_debug_errno(r, "Failed to load conf file %s: %m", *p);
+        }
+
+        return result;
+}
+
+static int install_info_follow(
+                InstallContext *c,
+                UnitFileInstallInfo *i,
+                const char *root_dir,
+                SearchFlags flags,
+                bool ignore_different_name) {
+
+        assert(c);
+        assert(i);
+
+        if (i->type != UNIT_FILE_TYPE_SYMLINK)
+                return -EINVAL;
+        if (!i->symlink_target)
+                return -EINVAL;
+
+        /* If the basename doesn't match, the caller should add a
+         * complete new entry for this. */
+
+        if (!ignore_different_name && !streq(basename(i->symlink_target), i->name))
+                return -EXDEV;
+
+        free_and_replace(i->path, i->symlink_target);
+        i->type = _UNIT_FILE_TYPE_INVALID;
+
+        return unit_file_load_or_readlink(c, i, i->path, root_dir, flags);
+}
+
+/**
+ * Search for the unit file. If the unit name is a symlink, follow the symlink to the
+ * target, maybe more than once. Propagate the instance name if present.
+ */
+static int install_info_traverse(
+                UnitFileScope scope,
+                InstallContext *c,
+                const LookupPaths *paths,
+                UnitFileInstallInfo *start,
+                SearchFlags flags,
+                UnitFileInstallInfo **ret) {
+
+        UnitFileInstallInfo *i;
+        unsigned k = 0;
+        int r;
+
+        assert(paths);
+        assert(start);
+        assert(c);
+
+        r = unit_file_search(c, start, paths, flags);
+        if (r < 0)
+                return r;
+
+        i = start;
+        while (i->type == UNIT_FILE_TYPE_SYMLINK) {
+                /* Follow the symlink */
+
+                if (++k > UNIT_FILE_FOLLOW_SYMLINK_MAX)
+                        return -ELOOP;
+
+                if (!(flags & SEARCH_FOLLOW_CONFIG_SYMLINKS)) {
+                        r = path_is_config(paths, i->path, true);
+                        if (r < 0)
+                                return r;
+                        if (r > 0)
+                                return -ELOOP;
+                }
+
+                r = install_info_follow(c, i, paths->root_dir, flags, false);
+                if (r == -EXDEV) {
+                        _cleanup_free_ char *buffer = NULL;
+                        const char *bn;
+
+                        /* Target has a different name, create a new
+                         * install info object for that, and continue
+                         * with that. */
+
+                        bn = basename(i->symlink_target);
+
+                        if (unit_name_is_valid(i->name, UNIT_NAME_INSTANCE) &&
+                            unit_name_is_valid(bn, UNIT_NAME_TEMPLATE)) {
+
+                                _cleanup_free_ char *instance = NULL;
+
+                                r = unit_name_to_instance(i->name, &instance);
+                                if (r < 0)
+                                        return r;
+
+                                r = unit_name_replace_instance(bn, instance, &buffer);
+                                if (r < 0)
+                                        return r;
+
+                                if (streq(buffer, i->name)) {
+
+                                        /* We filled in the instance, and the target stayed the same? If so, then let's
+                                         * honour the link as it is. */
+
+                                        r = install_info_follow(c, i, paths->root_dir, flags, true);
+                                        if (r < 0)
+                                                return r;
+
+                                        continue;
+                                }
+
+                                bn = buffer;
+                        }
+
+                        r = install_info_add(c, bn, NULL, false, &i);
+                        if (r < 0)
+                                return r;
+
+                        /* Try again, with the new target we found. */
+                        r = unit_file_search(c, i, paths, flags);
+                        if (r == -ENOENT)
+                                /* Translate error code to highlight this specific case */
+                                return -ENOLINK;
+                }
+
+                if (r < 0)
+                        return r;
+        }
+
+        if (ret)
+                *ret = i;
+
+        return 0;
+}
+
+/**
+ * Call install_info_add() with name_or_path as the path (if name_or_path starts with "/")
+ * or the name (otherwise). root_dir is prepended to the path.
+ */
+static int install_info_add_auto(
+                InstallContext *c,
+                const LookupPaths *paths,
+                const char *name_or_path,
+                UnitFileInstallInfo **ret) {
+
+        assert(c);
+        assert(name_or_path);
+
+        if (path_is_absolute(name_or_path)) {
+                const char *pp;
+
+                pp = prefix_roota(paths->root_dir, name_or_path);
+
+                return install_info_add(c, NULL, pp, false, ret);
+        } else
+                return install_info_add(c, name_or_path, NULL, false, ret);
+}
+
+static int install_info_discover(
+                UnitFileScope scope,
+                InstallContext *c,
+                const LookupPaths *paths,
+                const char *name,
+                SearchFlags flags,
+                UnitFileInstallInfo **ret,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+
+        UnitFileInstallInfo *i;
+        int r;
+
+        assert(c);
+        assert(paths);
+        assert(name);
+
+        r = install_info_add_auto(c, paths, name, &i);
+        if (r >= 0)
+                r = install_info_traverse(scope, c, paths, i, flags, ret);
+
+        if (r < 0)
+                unit_file_changes_add(changes, n_changes, r, name, NULL);
+        return r;
+}
+
+static int install_info_discover_and_check(
+                        UnitFileScope scope,
+                        InstallContext *c,
+                        const LookupPaths *paths,
+                        const char *name,
+                        SearchFlags flags,
+                        UnitFileInstallInfo **ret,
+                        UnitFileChange **changes,
+                        size_t *n_changes) {
+
+        int r;
+
+        r = install_info_discover(scope, c, paths, name, flags, ret, changes, n_changes);
+        if (r < 0)
+                return r;
+
+        return install_info_may_process(ret ? *ret : NULL, paths, changes, n_changes);
+}
+
+static int install_info_symlink_alias(
+                UnitFileInstallInfo *i,
+                const LookupPaths *paths,
+                const char *config_path,
+                bool force,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+
+        char **s;
+        int r = 0, q;
+
+        assert(i);
+        assert(paths);
+        assert(config_path);
+
+        STRV_FOREACH(s, i->aliases) {
+                _cleanup_free_ char *alias_path = NULL, *dst = NULL;
+
+                q = install_full_printf(i, *s, &dst);
+                if (q < 0)
+                        return q;
+
+                alias_path = path_make_absolute(dst, config_path);
+                if (!alias_path)
+                        return -ENOMEM;
+
+                q = create_symlink(paths, i->path, alias_path, force, changes, n_changes);
+                if (r == 0)
+                        r = q;
+        }
+
+        return r;
+}
+
+static int install_info_symlink_wants(
+                UnitFileInstallInfo *i,
+                const LookupPaths *paths,
+                const char *config_path,
+                char **list,
+                const char *suffix,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+
+        _cleanup_free_ char *buf = NULL;
+        const char *n;
+        char **s;
+        int r = 0, q;
+
+        assert(i);
+        assert(paths);
+        assert(config_path);
+
+        if (strv_isempty(list))
+                return 0;
+
+        if (unit_name_is_valid(i->name, UNIT_NAME_TEMPLATE)) {
+                UnitFileInstallInfo instance = {
+                        .type = _UNIT_FILE_TYPE_INVALID,
+                };
+                _cleanup_free_ char *path = NULL;
+
+                /* If this is a template, and we have no instance, don't do anything */
+                if (!i->default_instance)
+                        return 1;
+
+                r = unit_name_replace_instance(i->name, i->default_instance, &buf);
+                if (r < 0)
+                        return r;
+
+                instance.name = buf;
+                r = unit_file_search(NULL, &instance, paths, SEARCH_FOLLOW_CONFIG_SYMLINKS);
+                if (r < 0)
+                        return r;
+
+                path = TAKE_PTR(instance.path);
+
+                if (instance.type == UNIT_FILE_TYPE_MASKED) {
+                        unit_file_changes_add(changes, n_changes, -ERFKILL, path, NULL);
+                        return -ERFKILL;
+                }
+
+                n = buf;
+        } else
+                n = i->name;
+
+        STRV_FOREACH(s, list) {
+                _cleanup_free_ char *path = NULL, *dst = NULL;
+
+                q = install_full_printf(i, *s, &dst);
+                if (q < 0)
+                        return q;
+
+                if (!unit_name_is_valid(dst, UNIT_NAME_ANY)) {
+                        r = -EINVAL;
+                        continue;
+                }
+
+                path = strjoin(config_path, "/", dst, suffix, n);
+                if (!path)
+                        return -ENOMEM;
+
+                q = create_symlink(paths, i->path, path, true, changes, n_changes);
+                if (r == 0)
+                        r = q;
+        }
+
+        return r;
+}
+
+static int install_info_symlink_link(
+                UnitFileInstallInfo *i,
+                const LookupPaths *paths,
+                const char *config_path,
+                bool force,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+
+        _cleanup_free_ char *path = NULL;
+        int r;
+
+        assert(i);
+        assert(paths);
+        assert(config_path);
+        assert(i->path);
+
+        r = in_search_path(paths, i->path);
+        if (r < 0)
+                return r;
+        if (r > 0)
+                return 0;
+
+        path = strjoin(config_path, "/", i->name);
+        if (!path)
+                return -ENOMEM;
+
+        return create_symlink(paths, i->path, path, force, changes, n_changes);
+}
+
+static int install_info_apply(
+                UnitFileInstallInfo *i,
+                const LookupPaths *paths,
+                const char *config_path,
+                bool force,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+
+        int r, q;
+
+        assert(i);
+        assert(paths);
+        assert(config_path);
+
+        if (i->type != UNIT_FILE_TYPE_REGULAR)
+                return 0;
+
+        r = install_info_symlink_alias(i, paths, config_path, force, changes, n_changes);
+
+        q = install_info_symlink_wants(i, paths, config_path, i->wanted_by, ".wants/", changes, n_changes);
+        if (r == 0)
+                r = q;
+
+        q = install_info_symlink_wants(i, paths, config_path, i->required_by, ".requires/", changes, n_changes);
+        if (r == 0)
+                r = q;
+
+        q = install_info_symlink_link(i, paths, config_path, force, changes, n_changes);
+        /* Do not count links to the unit file towards the "carries_install_info" count */
+        if (r == 0 && q < 0)
+                r = q;
+
+        return r;
+}
+
+static int install_context_apply(
+                UnitFileScope scope,
+                InstallContext *c,
+                const LookupPaths *paths,
+                const char *config_path,
+                bool force,
+                SearchFlags flags,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+
+        UnitFileInstallInfo *i;
+        int r;
+
+        assert(c);
+        assert(paths);
+        assert(config_path);
+
+        if (ordered_hashmap_isempty(c->will_process))
+                return 0;
+
+        r = ordered_hashmap_ensure_allocated(&c->have_processed, &string_hash_ops);
+        if (r < 0)
+                return r;
+
+        r = 0;
+        while ((i = ordered_hashmap_first(c->will_process))) {
+                int q;
+
+                q = ordered_hashmap_move_one(c->have_processed, c->will_process, i->name);
+                if (q < 0)
+                        return q;
+
+                q = install_info_traverse(scope, c, paths, i, flags, NULL);
+                if (q < 0) {
+                        unit_file_changes_add(changes, n_changes, r, i->name, NULL);
+                        return q;
+                }
+
+                /* We can attempt to process a masked unit when a different unit
+                 * that we were processing specifies it in Also=. */
+                if (i->type == UNIT_FILE_TYPE_MASKED) {
+                        unit_file_changes_add(changes, n_changes, UNIT_FILE_IS_MASKED, i->path, NULL);
+                        if (r >= 0)
+                                /* Assume that something *could* have been enabled here,
+                                 * avoid "empty [Install] section" warning. */
+                                r += 1;
+                        continue;
+                }
+
+                if (i->type != UNIT_FILE_TYPE_REGULAR)
+                        continue;
+
+                q = install_info_apply(i, paths, config_path, force, changes, n_changes);
+                if (r >= 0) {
+                        if (q < 0)
+                                r = q;
+                        else
+                                r += q;
+                }
+        }
+
+        return r;
+}
+
+static int install_context_mark_for_removal(
+                UnitFileScope scope,
+                InstallContext *c,
+                const LookupPaths *paths,
+                Set **remove_symlinks_to,
+                const char *config_path,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+
+        UnitFileInstallInfo *i;
+        int r;
+
+        assert(c);
+        assert(paths);
+        assert(config_path);
+
+        /* Marks all items for removal */
+
+        if (ordered_hashmap_isempty(c->will_process))
+                return 0;
+
+        r = ordered_hashmap_ensure_allocated(&c->have_processed, &string_hash_ops);
+        if (r < 0)
+                return r;
+
+        while ((i = ordered_hashmap_first(c->will_process))) {
+
+                r = ordered_hashmap_move_one(c->have_processed, c->will_process, i->name);
+                if (r < 0)
+                        return r;
+
+                r = install_info_traverse(scope, c, paths, i, SEARCH_LOAD|SEARCH_FOLLOW_CONFIG_SYMLINKS, NULL);
+                if (r == -ENOLINK) {
+                        log_debug_errno(r, "Name %s leads to a dangling symlink, removing name.", i->name);
+                        unit_file_changes_add(changes, n_changes, UNIT_FILE_IS_DANGLING, i->path ?: i->name, NULL);
+                } else if (r == -ENOENT) {
+
+                        if (i->auxiliary)  /* some unit specified in Also= or similar is missing */
+                                log_debug_errno(r, "Auxiliary unit of %s not found, removing name.", i->name);
+                        else {
+                                log_debug_errno(r, "Unit %s not found, removing name.", i->name);
+                                unit_file_changes_add(changes, n_changes, r, i->path ?: i->name, NULL);
+                        }
+
+                } else if (r < 0) {
+                        log_debug_errno(r, "Failed to find unit %s, removing name: %m", i->name);
+                        unit_file_changes_add(changes, n_changes, r, i->path ?: i->name, NULL);
+                } else if (i->type == UNIT_FILE_TYPE_MASKED) {
+                        log_debug("Unit file %s is masked, ignoring.", i->name);
+                        unit_file_changes_add(changes, n_changes, UNIT_FILE_IS_MASKED, i->path ?: i->name, NULL);
+                        continue;
+                } else if (i->type != UNIT_FILE_TYPE_REGULAR) {
+                        log_debug("Unit %s has type %s, ignoring.", i->name, unit_file_type_to_string(i->type) ?: "invalid");
+                        continue;
+                }
+
+                r = mark_symlink_for_removal(remove_symlinks_to, i->name);
+                if (r < 0)
+                        return r;
+        }
+
+        return 0;
+}
+
+int unit_file_mask(
+                UnitFileScope scope,
+                UnitFileFlags flags,
+                const char *root_dir,
+                char **files,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+
+        _cleanup_(lookup_paths_free) LookupPaths paths = {};
+        const char *config_path;
+        char **i;
+        int r;
+
+        assert(scope >= 0);
+        assert(scope < _UNIT_FILE_SCOPE_MAX);
+
+        r = lookup_paths_init(&paths, scope, 0, root_dir);
+        if (r < 0)
+                return r;
+
+        config_path = (flags & UNIT_FILE_RUNTIME) ? paths.runtime_config : paths.persistent_config;
+        if (!config_path)
+                return -ENXIO;
+
+        STRV_FOREACH(i, files) {
+                _cleanup_free_ char *path = NULL;
+                int q;
+
+                if (!unit_name_is_valid(*i, UNIT_NAME_ANY)) {
+                        if (r == 0)
+                                r = -EINVAL;
+                        continue;
+                }
+
+                path = path_make_absolute(*i, config_path);
+                if (!path)
+                        return -ENOMEM;
+
+                q = create_symlink(&paths, "/dev/null", path, !!(flags & UNIT_FILE_FORCE), changes, n_changes);
+                if (q < 0 && r >= 0)
+                        r = q;
+        }
+
+        return r;
+}
+
+int unit_file_unmask(
+                UnitFileScope scope,
+                UnitFileFlags flags,
+                const char *root_dir,
+                char **files,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+
+        _cleanup_(lookup_paths_free) LookupPaths paths = {};
+        _cleanup_set_free_free_ Set *remove_symlinks_to = NULL;
+        _cleanup_strv_free_ char **todo = NULL;
+        size_t n_todo = 0, n_allocated = 0;
+        const char *config_path;
+        char **i;
+        bool dry_run;
+        int r, q;
+
+        assert(scope >= 0);
+        assert(scope < _UNIT_FILE_SCOPE_MAX);
+
+        r = lookup_paths_init(&paths, scope, 0, root_dir);
+        if (r < 0)
+                return r;
+
+        config_path = (flags & UNIT_FILE_RUNTIME) ? paths.runtime_config : paths.persistent_config;
+        if (!config_path)
+                return -ENXIO;
+
+        dry_run = !!(flags & UNIT_FILE_DRY_RUN);
+
+        STRV_FOREACH(i, files) {
+                _cleanup_free_ char *path = NULL;
+
+                if (!unit_name_is_valid(*i, UNIT_NAME_ANY))
+                        return -EINVAL;
+
+                path = path_make_absolute(*i, config_path);
+                if (!path)
+                        return -ENOMEM;
+
+                r = null_or_empty_path(path);
+                if (r == -ENOENT)
+                        continue;
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        continue;
+
+                if (!GREEDY_REALLOC0(todo, n_allocated, n_todo + 2))
+                        return -ENOMEM;
+
+                todo[n_todo] = strdup(*i);
+                if (!todo[n_todo])
+                        return -ENOMEM;
+
+                n_todo++;
+        }
+
+        strv_uniq(todo);
+
+        r = 0;
+        STRV_FOREACH(i, todo) {
+                _cleanup_free_ char *path = NULL;
+                const char *rp;
+
+                path = path_make_absolute(*i, config_path);
+                if (!path)
+                        return -ENOMEM;
+
+                if (!dry_run && unlink(path) < 0) {
+                        if (errno != ENOENT) {
+                                if (r >= 0)
+                                        r = -errno;
+                                unit_file_changes_add(changes, n_changes, -errno, path, NULL);
+                        }
+
+                        continue;
+                }
+
+                unit_file_changes_add(changes, n_changes, UNIT_FILE_UNLINK, path, NULL);
+
+                rp = skip_root(&paths, path);
+                q = mark_symlink_for_removal(&remove_symlinks_to, rp ?: path);
+                if (q < 0)
+                        return q;
+        }
+
+        q = remove_marked_symlinks(remove_symlinks_to, config_path, &paths, dry_run, changes, n_changes);
+        if (r >= 0)
+                r = q;
+
+        return r;
+}
+
+int unit_file_link(
+                UnitFileScope scope,
+                UnitFileFlags flags,
+                const char *root_dir,
+                char **files,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+
+        _cleanup_(lookup_paths_free) LookupPaths paths = {};
+        _cleanup_strv_free_ char **todo = NULL;
+        size_t n_todo = 0, n_allocated = 0;
+        const char *config_path;
+        char **i;
+        int r, q;
+
+        assert(scope >= 0);
+        assert(scope < _UNIT_FILE_SCOPE_MAX);
+
+        r = lookup_paths_init(&paths, scope, 0, root_dir);
+        if (r < 0)
+                return r;
+
+        config_path = (flags & UNIT_FILE_RUNTIME) ? paths.runtime_config : paths.persistent_config;
+        if (!config_path)
+                return -ENXIO;
+
+        STRV_FOREACH(i, files) {
+                _cleanup_free_ char *full = NULL;
+                struct stat st;
+                char *fn;
+
+                if (!path_is_absolute(*i))
+                        return -EINVAL;
+
+                fn = basename(*i);
+                if (!unit_name_is_valid(fn, UNIT_NAME_ANY))
+                        return -EINVAL;
+
+                full = prefix_root(paths.root_dir, *i);
+                if (!full)
+                        return -ENOMEM;
+
+                if (lstat(full, &st) < 0)
+                        return -errno;
+                r = stat_verify_regular(&st);
+                if (r < 0)
+                        return r;
+
+                q = in_search_path(&paths, *i);
+                if (q < 0)
+                        return q;
+                if (q > 0)
+                        continue;
+
+                if (!GREEDY_REALLOC0(todo, n_allocated, n_todo + 2))
+                        return -ENOMEM;
+
+                todo[n_todo] = strdup(*i);
+                if (!todo[n_todo])
+                        return -ENOMEM;
+
+                n_todo++;
+        }
+
+        strv_uniq(todo);
+
+        r = 0;
+        STRV_FOREACH(i, todo) {
+                _cleanup_free_ char *new_path = NULL;
+
+                new_path = path_make_absolute(basename(*i), config_path);
+                if (!new_path)
+                        return -ENOMEM;
+
+                q = create_symlink(&paths, *i, new_path, !!(flags & UNIT_FILE_FORCE), changes, n_changes);
+                if (q < 0 && r >= 0)
+                        r = q;
+        }
+
+        return r;
+}
+
+static int path_shall_revert(const LookupPaths *paths, const char *path) {
+        int r;
+
+        assert(paths);
+        assert(path);
+
+        /* Checks whether the path is one where the drop-in directories shall be removed. */
+
+        r = path_is_config(paths, path, true);
+        if (r != 0)
+                return r;
+
+        r = path_is_control(paths, path);
+        if (r != 0)
+                return r;
+
+        return path_is_transient(paths, path);
+}
+
+int unit_file_revert(
+                UnitFileScope scope,
+                const char *root_dir,
+                char **files,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+
+        _cleanup_set_free_free_ Set *remove_symlinks_to = NULL;
+        _cleanup_(lookup_paths_free) LookupPaths paths = {};
+        _cleanup_strv_free_ char **todo = NULL;
+        size_t n_todo = 0, n_allocated = 0;
+        char **i;
+        int r, q;
+
+        /* Puts a unit file back into vendor state. This means:
+         *
+         * a) we remove all drop-in snippets added by the user ("config"), add to transient units ("transient"), and
+         *    added via "systemctl set-property" ("control"), but not if the drop-in is generated ("generated").
+         *
+         * c) if there's a vendor unit file (i.e. one in /usr) we remove any configured overriding unit files (i.e. in
+         *    "config", but not in "transient" or "control" or even "generated").
+         *
+         * We remove all that in both the runtime and the persistent directories, if that applies.
+         */
+
+        r = lookup_paths_init(&paths, scope, 0, root_dir);
+        if (r < 0)
+                return r;
+
+        STRV_FOREACH(i, files) {
+                bool has_vendor = false;
+                char **p;
+
+                if (!unit_name_is_valid(*i, UNIT_NAME_ANY))
+                        return -EINVAL;
+
+                STRV_FOREACH(p, paths.search_path) {
+                        _cleanup_free_ char *path = NULL, *dropin = NULL;
+                        struct stat st;
+
+                        path = path_make_absolute(*i, *p);
+                        if (!path)
+                                return -ENOMEM;
+
+                        r = lstat(path, &st);
+                        if (r < 0) {
+                                if (errno != ENOENT)
+                                        return -errno;
+                        } else if (S_ISREG(st.st_mode)) {
+                                /* Check if there's a vendor version */
+                                r = path_is_vendor(&paths, path);
+                                if (r < 0)
+                                        return r;
+                                if (r > 0)
+                                        has_vendor = true;
+                        }
+
+                        dropin = strappend(path, ".d");
+                        if (!dropin)
+                                return -ENOMEM;
+
+                        r = lstat(dropin, &st);
+                        if (r < 0) {
+                                if (errno != ENOENT)
+                                        return -errno;
+                        } else if (S_ISDIR(st.st_mode)) {
+                                /* Remove the drop-ins */
+                                r = path_shall_revert(&paths, dropin);
+                                if (r < 0)
+                                        return r;
+                                if (r > 0) {
+                                        if (!GREEDY_REALLOC0(todo, n_allocated, n_todo + 2))
+                                                return -ENOMEM;
+
+                                        todo[n_todo++] = TAKE_PTR(dropin);
+                                }
+                        }
+                }
+
+                if (!has_vendor)
+                        continue;
+
+                /* OK, there's a vendor version, hence drop all configuration versions */
+                STRV_FOREACH(p, paths.search_path) {
+                        _cleanup_free_ char *path = NULL;
+                        struct stat st;
+
+                        path = path_make_absolute(*i, *p);
+                        if (!path)
+                                return -ENOMEM;
+
+                        r = lstat(path, &st);
+                        if (r < 0) {
+                                if (errno != ENOENT)
+                                        return -errno;
+                        } else if (S_ISREG(st.st_mode) || S_ISLNK(st.st_mode)) {
+                                r = path_is_config(&paths, path, true);
+                                if (r < 0)
+                                        return r;
+                                if (r > 0) {
+                                        if (!GREEDY_REALLOC0(todo, n_allocated, n_todo + 2))
+                                                return -ENOMEM;
+
+                                        todo[n_todo++] = TAKE_PTR(path);
+                                }
+                        }
+                }
+        }
+
+        strv_uniq(todo);
+
+        r = 0;
+        STRV_FOREACH(i, todo) {
+                _cleanup_strv_free_ char **fs = NULL;
+                const char *rp;
+                char **j;
+
+                (void) get_files_in_directory(*i, &fs);
+
+                q = rm_rf(*i, REMOVE_ROOT|REMOVE_PHYSICAL);
+                if (q < 0 && q != -ENOENT && r >= 0) {
+                        r = q;
+                        continue;
+                }
+
+                STRV_FOREACH(j, fs) {
+                        _cleanup_free_ char *t = NULL;
+
+                        t = strjoin(*i, "/", *j);
+                        if (!t)
+                                return -ENOMEM;
+
+                        unit_file_changes_add(changes, n_changes, UNIT_FILE_UNLINK, t, NULL);
+                }
+
+                unit_file_changes_add(changes, n_changes, UNIT_FILE_UNLINK, *i, NULL);
+
+                rp = skip_root(&paths, *i);
+                q = mark_symlink_for_removal(&remove_symlinks_to, rp ?: *i);
+                if (q < 0)
+                        return q;
+        }
+
+        q = remove_marked_symlinks(remove_symlinks_to, paths.runtime_config, &paths, false, changes, n_changes);
+        if (r >= 0)
+                r = q;
+
+        q = remove_marked_symlinks(remove_symlinks_to, paths.persistent_config, &paths, false, changes, n_changes);
+        if (r >= 0)
+                r = q;
+
+        return r;
+}
+
+int unit_file_add_dependency(
+                UnitFileScope scope,
+                UnitFileFlags flags,
+                const char *root_dir,
+                char **files,
+                const char *target,
+                UnitDependency dep,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+
+        _cleanup_(lookup_paths_free) LookupPaths paths = {};
+        _cleanup_(install_context_done) InstallContext c = {};
+        UnitFileInstallInfo *i, *target_info;
+        const char *config_path;
+        char **f;
+        int r;
+
+        assert(scope >= 0);
+        assert(scope < _UNIT_FILE_SCOPE_MAX);
+        assert(target);
+
+        if (!IN_SET(dep, UNIT_WANTS, UNIT_REQUIRES))
+                return -EINVAL;
+
+        if (!unit_name_is_valid(target, UNIT_NAME_ANY))
+                return -EINVAL;
+
+        r = lookup_paths_init(&paths, scope, 0, root_dir);
+        if (r < 0)
+                return r;
+
+        config_path = (flags & UNIT_FILE_RUNTIME) ? paths.runtime_config : paths.persistent_config;
+        if (!config_path)
+                return -ENXIO;
+
+        r = install_info_discover_and_check(scope, &c, &paths, target, SEARCH_FOLLOW_CONFIG_SYMLINKS,
+                                            &target_info, changes, n_changes);
+        if (r < 0)
+                return r;
+
+        assert(target_info->type == UNIT_FILE_TYPE_REGULAR);
+
+        STRV_FOREACH(f, files) {
+                char ***l;
+
+                r = install_info_discover_and_check(scope, &c, &paths, *f, SEARCH_FOLLOW_CONFIG_SYMLINKS,
+                                                    &i, changes, n_changes);
+                if (r < 0)
+                        return r;
+
+                assert(i->type == UNIT_FILE_TYPE_REGULAR);
+
+                /* We didn't actually load anything from the unit
+                 * file, but instead just add in our new symlink to
+                 * create. */
+
+                if (dep == UNIT_WANTS)
+                        l = &i->wanted_by;
+                else
+                        l = &i->required_by;
+
+                strv_free(*l);
+                *l = strv_new(target_info->name);
+                if (!*l)
+                        return -ENOMEM;
+        }
+
+        return install_context_apply(scope, &c, &paths, config_path, !!(flags & UNIT_FILE_FORCE), SEARCH_FOLLOW_CONFIG_SYMLINKS, changes, n_changes);
+}
+
+int unit_file_enable(
+                UnitFileScope scope,
+                UnitFileFlags flags,
+                const char *root_dir,
+                char **files,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+
+        _cleanup_(lookup_paths_free) LookupPaths paths = {};
+        _cleanup_(install_context_done) InstallContext c = {};
+        const char *config_path;
+        UnitFileInstallInfo *i;
+        char **f;
+        int r;
+
+        assert(scope >= 0);
+        assert(scope < _UNIT_FILE_SCOPE_MAX);
+
+        r = lookup_paths_init(&paths, scope, 0, root_dir);
+        if (r < 0)
+                return r;
+
+        config_path = (flags & UNIT_FILE_RUNTIME) ? paths.runtime_config : paths.persistent_config;
+        if (!config_path)
+                return -ENXIO;
+
+        STRV_FOREACH(f, files) {
+                r = install_info_discover_and_check(scope, &c, &paths, *f, SEARCH_LOAD|SEARCH_FOLLOW_CONFIG_SYMLINKS,
+                                                    &i, changes, n_changes);
+                if (r < 0)
+                        return r;
+
+                assert(i->type == UNIT_FILE_TYPE_REGULAR);
+        }
+
+        /* This will return the number of symlink rules that were
+           supposed to be created, not the ones actually created. This
+           is useful to determine whether the passed files had any
+           installation data at all. */
+
+        return install_context_apply(scope, &c, &paths, config_path, !!(flags & UNIT_FILE_FORCE), SEARCH_LOAD, changes, n_changes);
+}
+
+int unit_file_disable(
+                UnitFileScope scope,
+                UnitFileFlags flags,
+                const char *root_dir,
+                char **files,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+
+        _cleanup_(lookup_paths_free) LookupPaths paths = {};
+        _cleanup_(install_context_done) InstallContext c = {};
+        _cleanup_set_free_free_ Set *remove_symlinks_to = NULL;
+        const char *config_path;
+        char **i;
+        int r;
+
+        assert(scope >= 0);
+        assert(scope < _UNIT_FILE_SCOPE_MAX);
+
+        r = lookup_paths_init(&paths, scope, 0, root_dir);
+        if (r < 0)
+                return r;
+
+        config_path = (flags & UNIT_FILE_RUNTIME) ? paths.runtime_config : paths.persistent_config;
+        if (!config_path)
+                return -ENXIO;
+
+        STRV_FOREACH(i, files) {
+                if (!unit_name_is_valid(*i, UNIT_NAME_ANY))
+                        return -EINVAL;
+
+                r = install_info_add(&c, *i, NULL, false, NULL);
+                if (r < 0)
+                        return r;
+        }
+
+        r = install_context_mark_for_removal(scope, &c, &paths, &remove_symlinks_to, config_path, changes, n_changes);
+        if (r < 0)
+                return r;
+
+        return remove_marked_symlinks(remove_symlinks_to, config_path, &paths, !!(flags & UNIT_FILE_DRY_RUN), changes, n_changes);
+}
+
+int unit_file_reenable(
+                UnitFileScope scope,
+                UnitFileFlags flags,
+                const char *root_dir,
+                char **files,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+
+        char **n;
+        int r;
+        size_t l, i;
+
+        /* First, we invoke the disable command with only the basename... */
+        l = strv_length(files);
+        n = newa(char*, l+1);
+        for (i = 0; i < l; i++)
+                n[i] = basename(files[i]);
+        n[i] = NULL;
+
+        r = unit_file_disable(scope, flags, root_dir, n, changes, n_changes);
+        if (r < 0)
+                return r;
+
+        /* But the enable command with the full name */
+        return unit_file_enable(scope, flags, root_dir, files, changes, n_changes);
+}
+
+int unit_file_set_default(
+                UnitFileScope scope,
+                UnitFileFlags flags,
+                const char *root_dir,
+                const char *name,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+
+        _cleanup_(lookup_paths_free) LookupPaths paths = {};
+        _cleanup_(install_context_done) InstallContext c = {};
+        UnitFileInstallInfo *i;
+        const char *new_path;
+        int r;
+
+        assert(scope >= 0);
+        assert(scope < _UNIT_FILE_SCOPE_MAX);
+        assert(name);
+
+        if (unit_name_to_type(name) != UNIT_TARGET) /* this also validates the name */
+                return -EINVAL;
+        if (streq(name, SPECIAL_DEFAULT_TARGET))
+                return -EINVAL;
+
+        r = lookup_paths_init(&paths, scope, 0, root_dir);
+        if (r < 0)
+                return r;
+
+        r = install_info_discover_and_check(scope, &c, &paths, name, 0, &i, changes, n_changes);
+        if (r < 0)
+                return r;
+
+        new_path = strjoina(paths.persistent_config, "/" SPECIAL_DEFAULT_TARGET);
+        return create_symlink(&paths, i->path, new_path, !!(flags & UNIT_FILE_FORCE), changes, n_changes);
+}
+
+int unit_file_get_default(
+                UnitFileScope scope,
+                const char *root_dir,
+                char **name) {
+
+        _cleanup_(lookup_paths_free) LookupPaths paths = {};
+        _cleanup_(install_context_done) InstallContext c = {};
+        UnitFileInstallInfo *i;
+        char *n;
+        int r;
+
+        assert(scope >= 0);
+        assert(scope < _UNIT_FILE_SCOPE_MAX);
+        assert(name);
+
+        r = lookup_paths_init(&paths, scope, 0, root_dir);
+        if (r < 0)
+                return r;
+
+        r = install_info_discover(scope, &c, &paths, SPECIAL_DEFAULT_TARGET, SEARCH_FOLLOW_CONFIG_SYMLINKS,
+                                  &i, NULL, NULL);
+        if (r < 0)
+                return r;
+        r = install_info_may_process(i, &paths, NULL, 0);
+        if (r < 0)
+                return r;
+
+        n = strdup(i->name);
+        if (!n)
+                return -ENOMEM;
+
+        *name = n;
+        return 0;
+}
+
+int unit_file_lookup_state(
+                UnitFileScope scope,
+                const LookupPaths *paths,
+                const char *name,
+                UnitFileState *ret) {
+
+        _cleanup_(install_context_done) InstallContext c = {};
+        UnitFileInstallInfo *i;
+        UnitFileState state;
+        int r;
+
+        assert(paths);
+        assert(name);
+
+        if (!unit_name_is_valid(name, UNIT_NAME_ANY))
+                return -EINVAL;
+
+        r = install_info_discover(scope, &c, paths, name, SEARCH_LOAD|SEARCH_FOLLOW_CONFIG_SYMLINKS,
+                                  &i, NULL, NULL);
+        if (r < 0)
+                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)
+                return 0;
+
+        switch (i->type) {
+
+        case UNIT_FILE_TYPE_MASKED:
+                r = path_is_runtime(paths, i->path, true);
+                if (r < 0)
+                        return r;
+
+                state = r > 0 ? UNIT_FILE_MASKED_RUNTIME : UNIT_FILE_MASKED;
+                break;
+
+        case UNIT_FILE_TYPE_REGULAR:
+                r = path_is_generator(paths, i->path);
+                if (r < 0)
+                        return r;
+                if (r > 0) {
+                        state = UNIT_FILE_GENERATED;
+                        break;
+                }
+
+                r = path_is_transient(paths, i->path);
+                if (r < 0)
+                        return r;
+                if (r > 0) {
+                        state = UNIT_FILE_TRANSIENT;
+                        break;
+                }
+
+                /* Check if any of the Alias= symlinks have been created.
+                 * We ignore other aliases, and only check those that would
+                 * be created by systemctl enable for this unit. */
+                r = find_symlinks_in_scope(scope, paths, i, true, &state);
+                if (r < 0)
+                        return r;
+                if (r > 0)
+                        break;
+
+                /* Check if the file is known under other names. If it is,
+                 * it might be in use. Report that as UNIT_FILE_INDIRECT. */
+                r = find_symlinks_in_scope(scope, paths, i, false, &state);
+                if (r < 0)
+                        return r;
+                if (r > 0)
+                        state = UNIT_FILE_INDIRECT;
+                else {
+                        if (unit_file_install_info_has_rules(i))
+                                state = UNIT_FILE_DISABLED;
+                        else if (unit_file_install_info_has_also(i))
+                                state = UNIT_FILE_INDIRECT;
+                        else
+                                state = UNIT_FILE_STATIC;
+                }
+
+                break;
+
+        default:
+                assert_not_reached("Unexpect unit file type.");
+        }
+
+        *ret = state;
+        return 0;
+}
+
+int unit_file_get_state(
+                UnitFileScope scope,
+                const char *root_dir,
+                const char *name,
+                UnitFileState *ret) {
+
+        _cleanup_(lookup_paths_free) LookupPaths paths = {};
+        int r;
+
+        assert(scope >= 0);
+        assert(scope < _UNIT_FILE_SCOPE_MAX);
+        assert(name);
+
+        r = lookup_paths_init(&paths, scope, 0, root_dir);
+        if (r < 0)
+                return r;
+
+        return unit_file_lookup_state(scope, &paths, name, ret);
+}
+
+int unit_file_exists(UnitFileScope scope, const LookupPaths *paths, const char *name) {
+        _cleanup_(install_context_done) InstallContext c = {};
+        int r;
+
+        assert(paths);
+        assert(name);
+
+        if (!unit_name_is_valid(name, UNIT_NAME_ANY))
+                return -EINVAL;
+
+        r = install_info_discover(scope, &c, paths, name, 0, NULL, NULL, NULL);
+        if (r == -ENOENT)
+                return 0;
+        if (r < 0)
+                return r;
+
+        return 1;
+}
+
+static int split_pattern_into_name_and_instances(const char *pattern, char **out_unit_name, char ***out_instances) {
+        _cleanup_strv_free_ char **instances = NULL;
+        _cleanup_free_ char *unit_name = NULL;
+        int r;
+
+        assert(pattern);
+        assert(out_instances);
+        assert(out_unit_name);
+
+        r = extract_first_word(&pattern, &unit_name, NULL, 0);
+        if (r < 0)
+                return r;
+
+        /* We handle the instances logic when unit name is extracted */
+        if (pattern) {
+                /* We only create instances when a rule of templated unit
+                 * is seen. A rule like enable foo@.service a b c will
+                 * result in an array of (a, b, c) as instance names */
+                if (!unit_name_is_valid(unit_name, UNIT_NAME_TEMPLATE))
+                        return -EINVAL;
+
+                instances = strv_split(pattern, WHITESPACE);
+                if (!instances)
+                        return -ENOMEM;
+
+                *out_instances = TAKE_PTR(instances);
+        }
+
+        *out_unit_name = TAKE_PTR(unit_name);
+
+        return 0;
+}
+
+static int read_presets(UnitFileScope scope, const char *root_dir, Presets *presets) {
+        _cleanup_(presets_freep) Presets ps = {};
+        size_t n_allocated = 0;
+        _cleanup_strv_free_ char **files = NULL;
+        char **p;
+        int r;
+
+        assert(scope >= 0);
+        assert(scope < _UNIT_FILE_SCOPE_MAX);
+        assert(presets);
+
+        switch (scope) {
+        case UNIT_FILE_SYSTEM:
+                r = conf_files_list(&files, ".preset", root_dir, 0,
+                                    "/etc/systemd/system-preset",
+                                    "/run/systemd/system-preset",
+                                    "/usr/local/lib/systemd/system-preset",
+                                    "/usr/lib/systemd/system-preset",
+#if HAVE_SPLIT_USR
+                                    "/lib/systemd/system-preset",
+#endif
+                                    NULL);
+                break;
+
+        case UNIT_FILE_GLOBAL:
+        case UNIT_FILE_USER:
+                r = conf_files_list(&files, ".preset", root_dir, 0,
+                                    "/etc/systemd/user-preset",
+                                    "/run/systemd/user-preset",
+                                    "/usr/local/lib/systemd/user-preset",
+                                    "/usr/lib/systemd/user-preset",
+                                    NULL);
+                break;
+
+        default:
+                assert_not_reached("Invalid unit file scope");
+        }
+
+        if (r < 0)
+                return r;
+
+        STRV_FOREACH(p, files) {
+                _cleanup_fclose_ FILE *f;
+                int n = 0;
+
+                f = fopen(*p, "re");
+                if (!f) {
+                        if (errno == ENOENT)
+                                continue;
+
+                        return -errno;
+                }
+
+                for (;;) {
+                        _cleanup_free_ char *line = NULL;
+                        PresetRule rule = {};
+                        const char *parameter;
+                        char *l;
+
+                        r = read_line(f, LONG_LINE_MAX, &line);
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                break;
+
+                        l = strstrip(line);
+                        n++;
+
+                        if (isempty(l))
+                                continue;
+                        if (strchr(COMMENTS, *l))
+                                continue;
+
+                        parameter = first_word(l, "enable");
+                        if (parameter) {
+                                char *unit_name;
+                                char **instances = NULL;
+
+                                /* Unit_name will remain the same as parameter when no instances are specified */
+                                r = split_pattern_into_name_and_instances(parameter, &unit_name, &instances);
+                                if (r < 0) {
+                                        log_syntax(NULL, LOG_WARNING, *p, n, r, "Couldn't parse line '%s'. Ignoring.", line);
+                                        continue;
+                                }
+
+                                rule = (PresetRule) {
+                                        .pattern = unit_name,
+                                        .action = PRESET_ENABLE,
+                                        .instances = instances,
+                                };
+                        }
+
+                        parameter = first_word(l, "disable");
+                        if (parameter) {
+                                char *pattern;
+
+                                pattern = strdup(parameter);
+                                if (!pattern)
+                                        return -ENOMEM;
+
+                                rule = (PresetRule) {
+                                        .pattern = pattern,
+                                        .action = PRESET_DISABLE,
+                                };
+                        }
+
+                        if (rule.action) {
+                                if (!GREEDY_REALLOC(ps.rules, n_allocated, ps.n_rules + 1))
+                                        return -ENOMEM;
+
+                                ps.rules[ps.n_rules++] = rule;
+                                continue;
+                        }
+
+                        log_syntax(NULL, LOG_WARNING, *p, n, 0, "Couldn't parse line '%s'. Ignoring.", line);
+                }
+        }
+
+        *presets = ps;
+        ps = (Presets){};
+
+        return 0;
+}
+
+static int pattern_match_multiple_instances(
+                        const PresetRule rule,
+                        const char *unit_name,
+                        char ***ret) {
+
+        _cleanup_free_ char *templated_name = NULL;
+        int r;
+
+        /* If no ret is needed or the rule itself does not have instances
+         * initalized, we return not matching */
+        if (!ret || !rule.instances)
+                return 0;
+
+        r = unit_name_template(unit_name, &templated_name);
+        if (r < 0)
+                return r;
+        if (!streq(rule.pattern, templated_name))
+                return 0;
+
+        /* Compose a list of specified instances when unit name is a template  */
+        if (unit_name_is_valid(unit_name, UNIT_NAME_TEMPLATE)) {
+                _cleanup_free_ char *prefix = NULL;
+                _cleanup_strv_free_ char **out_strv = NULL;
+                char **iter;
+
+                r = unit_name_to_prefix(unit_name, &prefix);
+                if (r < 0)
+                        return r;
+
+                STRV_FOREACH(iter, rule.instances) {
+                        _cleanup_free_ char *name = NULL;
+                        r = unit_name_build(prefix, *iter, ".service", &name);
+                        if (r < 0)
+                                return r;
+                        r = strv_extend(&out_strv, name);
+                        if (r < 0)
+                                return r;
+                }
+
+                *ret = TAKE_PTR(out_strv);
+                return 1;
+        } else {
+                /* We now know the input unit name is an instance name */
+                _cleanup_free_ char *instance_name = NULL;
+
+                r = unit_name_to_instance(unit_name, &instance_name);
+                if (r < 0)
+                        return r;
+
+                if (strv_find(rule.instances, instance_name))
+                        return 1;
+        }
+        return 0;
+}
+
+static int query_presets(const char *name, const Presets presets, char ***instance_name_list) {
+        PresetAction action = PRESET_UNKNOWN;
+        size_t i;
+        char **s;
+        if (!unit_name_is_valid(name, UNIT_NAME_ANY))
+                return -EINVAL;
+
+        for (i = 0; i < presets.n_rules; i++)
+                if (pattern_match_multiple_instances(presets.rules[i], name, instance_name_list) > 0 ||
+                    fnmatch(presets.rules[i].pattern, name, FNM_NOESCAPE) == 0) {
+                        action = presets.rules[i].action;
+                        break;
+                }
+
+        switch (action) {
+        case PRESET_UNKNOWN:
+                log_debug("Preset files don't specify rule for %s. Enabling.", name);
+                return 1;
+        case PRESET_ENABLE:
+                if (instance_name_list && *instance_name_list)
+                        STRV_FOREACH(s, *instance_name_list)
+                                log_debug("Preset files say enable %s.", *s);
+                else
+                        log_debug("Preset files say enable %s.", name);
+                return 1;
+        case PRESET_DISABLE:
+                log_debug("Preset files say disable %s.", name);
+                return 0;
+        default:
+                assert_not_reached("invalid preset action");
+        }
+}
+
+int unit_file_query_preset(UnitFileScope scope, const char *root_dir, const char *name) {
+        _cleanup_(presets_freep) Presets presets = {};
+        int r;
+
+        r = read_presets(scope, root_dir, &presets);
+        if (r < 0)
+                return r;
+
+        return query_presets(name, presets, NULL);
+}
+
+static int execute_preset(
+                UnitFileScope scope,
+                InstallContext *plus,
+                InstallContext *minus,
+                const LookupPaths *paths,
+                const char *config_path,
+                char **files,
+                UnitFilePresetMode mode,
+                bool force,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+
+        int r;
+
+        assert(plus);
+        assert(minus);
+        assert(paths);
+        assert(config_path);
+
+        if (mode != UNIT_FILE_PRESET_ENABLE_ONLY) {
+                _cleanup_set_free_free_ Set *remove_symlinks_to = NULL;
+
+                r = install_context_mark_for_removal(scope, minus, paths, &remove_symlinks_to, config_path, changes, n_changes);
+                if (r < 0)
+                        return r;
+
+                r = remove_marked_symlinks(remove_symlinks_to, config_path, paths, false, changes, n_changes);
+        } else
+                r = 0;
+
+        if (mode != UNIT_FILE_PRESET_DISABLE_ONLY) {
+                int q;
+
+                /* Returns number of symlinks that where supposed to be installed. */
+                q = install_context_apply(scope, plus, paths, config_path, force, SEARCH_LOAD, changes, n_changes);
+                if (r >= 0) {
+                        if (q < 0)
+                                r = q;
+                        else
+                                r += q;
+                }
+        }
+
+        return r;
+}
+
+static int preset_prepare_one(
+                UnitFileScope scope,
+                InstallContext *plus,
+                InstallContext *minus,
+                LookupPaths *paths,
+                const char *name,
+                Presets presets,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+
+        _cleanup_(install_context_done) InstallContext tmp = {};
+        _cleanup_strv_free_ char **instance_name_list = NULL;
+        UnitFileInstallInfo *i;
+        int r;
+
+        if (install_info_find(plus, name) || install_info_find(minus, name))
+                return 0;
+
+        r = install_info_discover(scope, &tmp, paths, name, SEARCH_FOLLOW_CONFIG_SYMLINKS,
+                                  &i, changes, n_changes);
+        if (r < 0)
+                return r;
+        if (!streq(name, i->name)) {
+                log_debug("Skipping %s because it is an alias for %s.", name, i->name);
+                return 0;
+        }
+
+        r = query_presets(name, presets, &instance_name_list);
+        if (r < 0)
+                return r;
+
+        if (r > 0) {
+                if (instance_name_list) {
+                        char **s;
+                        STRV_FOREACH(s, instance_name_list) {
+                                r = install_info_discover_and_check(scope, plus, paths, *s, SEARCH_LOAD|SEARCH_FOLLOW_CONFIG_SYMLINKS,
+                                                                    &i, changes, n_changes);
+                                if (r < 0)
+                                        return r;
+                        }
+                } else {
+                        r = install_info_discover_and_check(scope, plus, paths, name, SEARCH_LOAD|SEARCH_FOLLOW_CONFIG_SYMLINKS,
+                                                            &i, changes, n_changes);
+                        if (r < 0)
+                                return r;
+                }
+
+        } else
+                r = install_info_discover(scope, minus, paths, name, SEARCH_FOLLOW_CONFIG_SYMLINKS,
+                                          &i, changes, n_changes);
+
+        return r;
+}
+
+int unit_file_preset(
+                UnitFileScope scope,
+                UnitFileFlags flags,
+                const char *root_dir,
+                char **files,
+                UnitFilePresetMode mode,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+
+        _cleanup_(install_context_done) InstallContext plus = {}, minus = {};
+        _cleanup_(lookup_paths_free) LookupPaths paths = {};
+        _cleanup_(presets_freep) Presets presets = {};
+        const char *config_path;
+        char **i;
+        int r;
+
+        assert(scope >= 0);
+        assert(scope < _UNIT_FILE_SCOPE_MAX);
+        assert(mode < _UNIT_FILE_PRESET_MAX);
+
+        r = lookup_paths_init(&paths, scope, 0, root_dir);
+        if (r < 0)
+                return r;
+
+        config_path = (flags & UNIT_FILE_RUNTIME) ? paths.runtime_config : paths.persistent_config;
+        if (!config_path)
+                return -ENXIO;
+
+        r = read_presets(scope, root_dir, &presets);
+        if (r < 0)
+                return r;
+
+        STRV_FOREACH(i, files) {
+                r = preset_prepare_one(scope, &plus, &minus, &paths, *i, presets, changes, n_changes);
+                if (r < 0)
+                        return r;
+        }
+
+        return execute_preset(scope, &plus, &minus, &paths, config_path, files, mode, !!(flags & UNIT_FILE_FORCE), changes, n_changes);
+}
+
+int unit_file_preset_all(
+                UnitFileScope scope,
+                UnitFileFlags flags,
+                const char *root_dir,
+                UnitFilePresetMode mode,
+                UnitFileChange **changes,
+                size_t *n_changes) {
+
+        _cleanup_(install_context_done) InstallContext plus = {}, minus = {};
+        _cleanup_(lookup_paths_free) LookupPaths paths = {};
+        _cleanup_(presets_freep) Presets presets = {};
+        const char *config_path = NULL;
+        char **i;
+        int r;
+
+        assert(scope >= 0);
+        assert(scope < _UNIT_FILE_SCOPE_MAX);
+        assert(mode < _UNIT_FILE_PRESET_MAX);
+
+        r = lookup_paths_init(&paths, scope, 0, root_dir);
+        if (r < 0)
+                return r;
+
+        config_path = (flags & UNIT_FILE_RUNTIME) ? paths.runtime_config : paths.persistent_config;
+        if (!config_path)
+                return -ENXIO;
+
+        r = read_presets(scope, root_dir, &presets);
+        if (r < 0)
+                return r;
+
+        STRV_FOREACH(i, paths.search_path) {
+                _cleanup_closedir_ DIR *d = NULL;
+                struct dirent *de;
+
+                d = opendir(*i);
+                if (!d) {
+                        if (errno == ENOENT)
+                                continue;
+
+                        return -errno;
+                }
+
+                FOREACH_DIRENT(de, d, return -errno) {
+
+                        if (!unit_name_is_valid(de->d_name, UNIT_NAME_ANY))
+                                continue;
+
+                        dirent_ensure_type(d, de);
+
+                        if (!IN_SET(de->d_type, DT_LNK, DT_REG))
+                                continue;
+
+                        /* we don't pass changes[] in, because we want to handle errors on our own */
+                        r = preset_prepare_one(scope, &plus, &minus, &paths, de->d_name, presets, NULL, 0);
+                        if (r == -ERFKILL)
+                                r = unit_file_changes_add(changes, n_changes,
+                                                          UNIT_FILE_IS_MASKED, de->d_name, NULL);
+                        else if (r == -ENOLINK)
+                                r = unit_file_changes_add(changes, n_changes,
+                                                          UNIT_FILE_IS_DANGLING, de->d_name, NULL);
+                        else if (r == -EADDRNOTAVAIL) /* Ignore generated/transient units when applying preset */
+                                continue;
+                        if (r < 0)
+                                return r;
+                }
+        }
+
+        return execute_preset(scope, &plus, &minus, &paths, config_path, NULL, mode, !!(flags & UNIT_FILE_FORCE), changes, n_changes);
+}
+
+static void unit_file_list_free_one(UnitFileList *f) {
+        if (!f)
+                return;
+
+        free(f->path);
+        free(f);
+}
+
+Hashmap* unit_file_list_free(Hashmap *h) {
+        return hashmap_free_with_destructor(h, unit_file_list_free_one);
+}
+
+DEFINE_TRIVIAL_CLEANUP_FUNC(UnitFileList*, unit_file_list_free_one);
+
+int unit_file_get_list(
+                UnitFileScope scope,
+                const char *root_dir,
+                Hashmap *h,
+                char **states,
+                char **patterns) {
+
+        _cleanup_(lookup_paths_free) LookupPaths paths = {};
+        char **i;
+        int r;
+
+        assert(scope >= 0);
+        assert(scope < _UNIT_FILE_SCOPE_MAX);
+        assert(h);
+
+        r = lookup_paths_init(&paths, scope, 0, root_dir);
+        if (r < 0)
+                return r;
+
+        STRV_FOREACH(i, paths.search_path) {
+                _cleanup_closedir_ DIR *d = NULL;
+                struct dirent *de;
+
+                d = opendir(*i);
+                if (!d) {
+                        if (errno == ENOENT)
+                                continue;
+                        if (IN_SET(errno, ENOTDIR, EACCES)) {
+                                log_debug_errno(errno, "Failed to open \"%s\": %m", *i);
+                                continue;
+                        }
+
+                        return -errno;
+                }
+
+                FOREACH_DIRENT(de, d, return -errno) {
+                        _cleanup_(unit_file_list_free_onep) UnitFileList *f = NULL;
+
+                        if (!unit_name_is_valid(de->d_name, UNIT_NAME_ANY))
+                                continue;
+
+                        if (!strv_fnmatch_or_empty(patterns, de->d_name, FNM_NOESCAPE))
+                                continue;
+
+                        if (hashmap_get(h, de->d_name))
+                                continue;
+
+                        dirent_ensure_type(d, de);
+
+                        if (!IN_SET(de->d_type, DT_LNK, DT_REG))
+                                continue;
+
+                        f = new0(UnitFileList, 1);
+                        if (!f)
+                                return -ENOMEM;
+
+                        f->path = path_make_absolute(de->d_name, *i);
+                        if (!f->path)
+                                return -ENOMEM;
+
+                        r = unit_file_lookup_state(scope, &paths, de->d_name, &f->state);
+                        if (r < 0)
+                                f->state = UNIT_FILE_BAD;
+
+                        if (!strv_isempty(states) &&
+                            !strv_contains(states, unit_file_state_to_string(f->state)))
+                                continue;
+
+                        r = hashmap_put(h, basename(f->path), f);
+                        if (r < 0)
+                                return r;
+
+                        f = NULL; /* prevent cleanup */
+                }
+        }
+
+        return 0;
+}
+
+static const char* const unit_file_state_table[_UNIT_FILE_STATE_MAX] = {
+        [UNIT_FILE_ENABLED] = "enabled",
+        [UNIT_FILE_ENABLED_RUNTIME] = "enabled-runtime",
+        [UNIT_FILE_LINKED] = "linked",
+        [UNIT_FILE_LINKED_RUNTIME] = "linked-runtime",
+        [UNIT_FILE_MASKED] = "masked",
+        [UNIT_FILE_MASKED_RUNTIME] = "masked-runtime",
+        [UNIT_FILE_STATIC] = "static",
+        [UNIT_FILE_DISABLED] = "disabled",
+        [UNIT_FILE_INDIRECT] = "indirect",
+        [UNIT_FILE_GENERATED] = "generated",
+        [UNIT_FILE_TRANSIENT] = "transient",
+        [UNIT_FILE_BAD] = "bad",
+};
+
+DEFINE_STRING_TABLE_LOOKUP(unit_file_state, UnitFileState);
+
+static const char* const unit_file_change_type_table[_UNIT_FILE_CHANGE_TYPE_MAX] = {
+        [UNIT_FILE_SYMLINK] = "symlink",
+        [UNIT_FILE_UNLINK] = "unlink",
+        [UNIT_FILE_IS_MASKED] = "masked",
+        [UNIT_FILE_IS_DANGLING] = "dangling",
+};
+
+DEFINE_STRING_TABLE_LOOKUP(unit_file_change_type, UnitFileChangeType);
+
+static const char* const unit_file_preset_mode_table[_UNIT_FILE_PRESET_MAX] = {
+        [UNIT_FILE_PRESET_FULL] = "full",
+        [UNIT_FILE_PRESET_ENABLE_ONLY] = "enable-only",
+        [UNIT_FILE_PRESET_DISABLE_ONLY] = "disable-only",
+};
+
+DEFINE_STRING_TABLE_LOOKUP(unit_file_preset_mode, UnitFilePresetMode);