core: parse rd.rescue and rd.emergency as initrd-specific shorthands (#3488)

Typing `rd.rescue` is easier than `rd.systemd.unit=rescue.target`.

src/basic/proc-cmdline.c

@@ -160,17 +160,29 @@ static const char * const rlmap[] = {
         "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) {
         size_t i;
+        const char * const *rlmap_ptr = in_initrd() ? rlmap_initrd
+                                                    : rlmap;
 
         if (!word)
                 return NULL;
 
-        for (i = 0; i < ELEMENTSOF(rlmap); i += 2)
-                if (streq(word, rlmap[i]))
-                        return rlmap[i+1];
+        if (in_initrd() && (word = startswith(word, "rd.")) == NULL)
+                return NULL;
+
+        for (i = 0; rlmap_ptr[i] != NULL; i += 2)
+                if (streq(word, rlmap_ptr[i]))
+                        return rlmap_ptr[i+1];
 
         return NULL;
 }

src/basic/util.c

@@ -64,6 +64,7 @@ assert_cc(EAGAIN == EWOULDBLOCK);
 
 int saved_argc = 0;
 char **saved_argv = NULL;
+static int saved_in_initrd = -1;
 
 size_t page_size(void) {
         static thread_local size_t pgsz = 0;
@@ -454,11 +455,10 @@ int fork_agent(pid_t *pid, const int except[], unsigned n_except, const char *pa
 }
 
 bool in_initrd(void) {
-        static int saved = -1;
         struct statfs s;
 
-        if (saved >= 0)
-                return saved;
+        if (saved_in_initrd >= 0)
+                return saved_in_initrd;
 
         /* We make two checks here:
          *
@@ -470,11 +470,15 @@ bool in_initrd(void) {
          * emptying when transititioning to the main systemd.
          */
 
-        saved = access("/etc/initrd-release", F_OK) >= 0 &&
-                statfs("/", &s) >= 0 &&
-                is_temporary_fs(&s);
+        saved_in_initrd = access("/etc/initrd-release", F_OK) >= 0 &&
+                          statfs("/", &s) >= 0 &&
+                          is_temporary_fs(&s);
 
-        return saved;
+        return saved_in_initrd;
+}
+
+void in_initrd_force(bool value) {
+        saved_in_initrd = value;
 }
 
 /* hey glibc, APIs with callbacks without a user pointer are so useless */

src/basic/util.h

@@ -86,6 +86,7 @@ int prot_from_flags(int flags) _const_;
 int fork_agent(pid_t *pid, const int except[], unsigned n_except, const char *path, ...);
 
 bool in_initrd(void);
+void in_initrd_force(bool value);
 
 void *xbsearch_r(const void *key, const void *base, size_t nmemb, size_t size,
                  int (*compar) (const void *, const void *, void *),