util-lib: move runlevel_to_target() to shared/unit-file

It if of course related to /proc/cmdline parsing, but is higher-level
functionality built on top of it. It should be in shared/ because it
is something to be used by pid1 and related utilities, not something for
level-level libraries.

src/shared/unit-file.c

@@ -6,6 +6,7 @@
 #include "macro.h"
 #include "path-lookup.h"
 #include "set.h"
+#include "special.h"
 #include "stat-util.h"
 #include "string-util.h"
 #include "strv.h"
@@ -511,3 +512,47 @@ int unit_file_find_fragment(
         // FIXME: if instance, consider any unit names with different template name
         return 0;
 }
+
+static const char * const rlmap[] = {
+        "emergency", SPECIAL_EMERGENCY_TARGET,
+        "-b",        SPECIAL_EMERGENCY_TARGET,
+        "rescue",    SPECIAL_RESCUE_TARGET,
+        "single",    SPECIAL_RESCUE_TARGET,
+        "-s",        SPECIAL_RESCUE_TARGET,
+        "s",         SPECIAL_RESCUE_TARGET,
+        "S",         SPECIAL_RESCUE_TARGET,
+        "1",         SPECIAL_RESCUE_TARGET,
+        "2",         SPECIAL_MULTI_USER_TARGET,
+        "3",         SPECIAL_MULTI_USER_TARGET,
+        "4",         SPECIAL_MULTI_USER_TARGET,
+        "5",         SPECIAL_GRAPHICAL_TARGET,
+        NULL
+};
+
+static const char * const rlmap_initrd[] = {
+        "emergency", SPECIAL_EMERGENCY_TARGET,
+        "rescue",    SPECIAL_RESCUE_TARGET,
+        NULL
+};
+
+const char* runlevel_to_target(const char *word) {
+        const char * const *rlmap_ptr;
+        size_t i;
+
+        if (!word)
+                return NULL;
+
+        if (in_initrd()) {
+                word = startswith(word, "rd.");
+                if (!word)
+                        return NULL;
+        }
+
+        rlmap_ptr = in_initrd() ? rlmap_initrd : rlmap;
+
+        for (i = 0; rlmap_ptr[i]; i += 2)
+                if (streq(word, rlmap_ptr[i]))
+                        return rlmap_ptr[i+1];
+
+        return NULL;
+}

src/shared/unit-file.h

@@ -54,3 +54,5 @@ int unit_file_find_fragment(
                 const char *unit_name,
                 const char **ret_fragment_path,
                 Set **names);
+
+const char* runlevel_to_target(const char *rl);