alloc-util: add free_many() helper

We often free an array of things. Let's create a common helper for this,
and port some potential users over. (Not all, too lazy for that for
now).

src/basic/alloc-util.h

@@ -242,4 +242,17 @@ static inline size_t malloc_sizeof_safe(void **xp) {
                 (char*) memdupa_suffix0(_t, strnlen(_t, (n)));          \
         })
 
+/* Free every element of the array. */
+static inline void free_many(void **p, size_t n) {
+        assert(p || n == 0);
+
+        FOREACH_ARRAY(i, p, n)
+                *i = mfree(*i);
+}
+
+/* Typesafe wrapper for char** rather than void**. Unfortunately C won't implicitly cast this. */
+static inline void free_many_charp(char **c, size_t n) {
+        free_many((void**) c, n);
+}
+
 #include "memory-util.h"

src/basic/cgroup-util.c

@@ -1915,9 +1915,7 @@ int cg_get_keyed_attribute_full(
         r = -ENXIO;
 
 fail:
-        for (i = 0; i < n; i++)
-                free(v[i]);
-
+        free_many_charp(v, n);
         return r;
 
 done:

src/basic/extract-word.c

@@ -272,11 +272,7 @@ int extract_many_words(const char **p, const char *separators, unsigned flags, .
 
                 r = extract_first_word(p, &l[c], separators, flags);
                 if (r < 0) {
-                        int j;
-
-                        for (j = 0; j < c; j++)
-                                free(l[j]);
-
+                        free_many_charp(l, c);
                         return r;
                 }
 

src/basic/locale-util.c

@@ -340,11 +340,7 @@ out:
 }
 
 void locale_variables_free(char *l[_VARIABLE_LC_MAX]) {
-        if (!l)
-                return;
-
-        for (LocaleVariable i = 0; i < _VARIABLE_LC_MAX; i++)
-                l[i] = mfree(l[i]);
+        free_many_charp(l, _VARIABLE_LC_MAX);
 }
 
 void locale_variables_simplify(char *l[_VARIABLE_LC_MAX]) {

src/basic/rlimit-util.c

@@ -359,13 +359,7 @@ int rlimit_from_string_harder(const char *s) {
 }
 
 void rlimit_free_all(struct rlimit **rl) {
-        int i;
-
-        if (!rl)
-                return;
-
-        for (i = 0; i < _RLIMIT_MAX; i++)
-                rl[i] = mfree(rl[i]);
+        free_many((void**) rl, _RLIMIT_MAX);
 }
 
 int rlimit_nofile_bump(int limit) {

src/basic/strv.c

@@ -212,9 +212,7 @@ int strv_extend_strv(char ***a, char * const *b, bool filter_duplicates) {
         return (int) i;
 
 rollback:
-        for (size_t j = 0; j < i; j++)
-                free(t[p + j]);
-
+        free_many_charp(t + p, i);
         t[p] = NULL;
         return -ENOMEM;
 }