bootctl: modernization

Use strjoina to avoid error handling, and openat to simplify things.

Some fixes on the way:
- ferror does not set errno, so the return value was wrong in some cases
- errors are propagated in more cases
- EFI/systemd was created, but EFI/systemd-boot was deleted
- something is always printed on error
- when checking the version, comparison was done against "systemd-bo" for some reason
- return value was converted from negative to EXIT_SUCCESS/EXIT_FAILURE twice,
  resulting in EXIT_SUCCESS all the time

src/shared/util.c

@@ -148,6 +148,27 @@ char* endswith(const char *s, const char *postfix) {
         return (char*) s + sl - pl;
 }
 
+char* endswith_no_case(const char *s, const char *postfix) {
+        size_t sl, pl;
+
+        assert(s);
+        assert(postfix);
+
+        sl = strlen(s);
+        pl = strlen(postfix);
+
+        if (pl == 0)
+                return (char*) s + sl;
+
+        if (sl < pl)
+                return NULL;
+
+        if (strcasecmp(s + sl - pl, postfix) != 0)
+                return NULL;
+
+        return (char*) s + sl - pl;
+}
+
 char* first_word(const char *s, const char *word) {
         size_t sl, wl;
         const char *p;

src/shared/util.h

@@ -134,6 +134,7 @@ static inline char *startswith_no_case(const char *s, const char *prefix) {
 }
 
 char *endswith(const char *s, const char *postfix) _pure_;
+char *endswith_no_case(const char *s, const char *postfix) _pure_;
 
 char *first_word(const char *s, const char *word) _pure_;