tree-wide: return NULL from freeing functions

I started working on this because I wanted to change how
DEFINE_TRIVIAL_CLEANUP_FUNC is defined. Even independently of that change, it's
nice to make make things more consistent and predictable.

src/shared/barrier.c

@@ -123,14 +123,15 @@ int barrier_create(Barrier *b) {
  *
  * If @b is NULL, this is a no-op.
  */
-void barrier_destroy(Barrier *b) {
+Barrier* barrier_destroy(Barrier *b) {
         if (!b)
-                return;
+                return NULL;
 
         b->me = safe_close(b->me);
         b->them = safe_close(b->them);
         safe_close_pair(b->pipe);
         b->barriers = 0;
+        return NULL;
 }
 
 /**

src/shared/barrier.h

@@ -37,7 +37,7 @@ struct Barrier {
 #define BARRIER_NULL {-1, -1, {-1, -1}, 0}
 
 int barrier_create(Barrier *obj);
-void barrier_destroy(Barrier *b);
+Barrier* barrier_destroy(Barrier *b);
 
 DEFINE_TRIVIAL_CLEANUP_FUNC(Barrier*, barrier_destroy);
 

src/shared/bitmap.c

@@ -24,11 +24,11 @@
 #define BITMAP_NUM_TO_REM(n)              ((n) % (sizeof(uint64_t) * 8))
 #define BITMAP_OFFSET_TO_NUM(offset, rem) ((offset) * sizeof(uint64_t) * 8 + (rem))
 
-Bitmap *bitmap_new(void) {
+Bitmap* bitmap_new(void) {
         return new0(Bitmap, 1);
 }
 
-Bitmap *bitmap_copy(Bitmap *b) {
+Bitmap* bitmap_copy(Bitmap *b) {
         Bitmap *ret;
 
         ret = bitmap_new();
@@ -43,12 +43,12 @@ Bitmap *bitmap_copy(Bitmap *b) {
         return ret;
 }
 
-void bitmap_free(Bitmap *b) {
+Bitmap* bitmap_free(Bitmap *b) {
         if (!b)
-                return;
+                return NULL;
 
         free(b->bitmaps);
-        free(b);
+        return mfree(b);
 }
 
 int bitmap_ensure_allocated(Bitmap **b) {

src/shared/bitmap.h

@@ -12,10 +12,10 @@ typedef struct Bitmap {
         size_t bitmaps_allocated;
 } Bitmap;
 
-Bitmap *bitmap_new(void);
-Bitmap *bitmap_copy(Bitmap *b);
+Bitmap* bitmap_new(void);
+Bitmap* bitmap_copy(Bitmap *b);
 int bitmap_ensure_allocated(Bitmap **b);
-void bitmap_free(Bitmap *b);
+Bitmap* bitmap_free(Bitmap *b);
 
 int bitmap_set(Bitmap *b, unsigned n);
 void bitmap_unset(Bitmap *b, unsigned n);

src/shared/bus-wait-for-jobs.c

@@ -61,9 +61,9 @@ static int match_job_removed(sd_bus_message *m, void *userdata, sd_bus_error *er
         return 0;
 }
 
-void bus_wait_for_jobs_free(BusWaitForJobs *d) {
+BusWaitForJobs* bus_wait_for_jobs_free(BusWaitForJobs *d) {
         if (!d)
-                return;
+                return NULL;
 
         set_free(d->jobs);
 
@@ -75,7 +75,7 @@ void bus_wait_for_jobs_free(BusWaitForJobs *d) {
         free(d->name);
         free(d->result);
 
-        free(d);
+        return mfree(d);
 }
 
 int bus_wait_for_jobs_new(sd_bus *bus, BusWaitForJobs **ret) {

src/shared/bus-wait-for-jobs.h

@@ -8,7 +8,7 @@
 typedef struct BusWaitForJobs BusWaitForJobs;
 
 int bus_wait_for_jobs_new(sd_bus *bus, BusWaitForJobs **ret);
-void bus_wait_for_jobs_free(BusWaitForJobs *d);
+BusWaitForJobs* bus_wait_for_jobs_free(BusWaitForJobs *d);
 int bus_wait_for_jobs_add(BusWaitForJobs *d, const char *path);
 int bus_wait_for_jobs(BusWaitForJobs *d, bool quiet, const char* const* extra_args);
 int bus_wait_for_jobs_one(BusWaitForJobs *d, const char *path, bool quiet);

src/shared/calendarspec.c

@@ -33,14 +33,13 @@
 /* Let's make sure that the microsecond component is safe to be stored in an 'int' */
 assert_cc(INT_MAX >= USEC_PER_SEC);
 
-static void chain_free(CalendarComponent *c) {
-        CalendarComponent *n;
-
+static CalendarComponent* chain_free(CalendarComponent *c) {
         while (c) {
-                n = c->next;
+                CalendarComponent *n = c->next;
                 free(c);
                 c = n;
         }
+        return NULL;
 }
 
 DEFINE_TRIVIAL_CLEANUP_FUNC(CalendarComponent*, chain_free);

src/shared/dissect-image.c

@@ -1681,12 +1681,12 @@ static int verity_can_reuse(
         return 0;
 }
 
-static inline void dm_deferred_remove_clean(char *name) {
+static inline char* dm_deferred_remove_clean(char *name) {
         if (!name)
-                return;
+                return NULL;
 
         (void) sym_crypt_deactivate_by_name(NULL, name, CRYPT_DEACTIVATE_DEFERRED);
-        free(name);
+        return mfree(name);
 }
 DEFINE_TRIVIAL_CLEANUP_FUNC(char *, dm_deferred_remove_clean);
 

src/shared/install.c

@@ -3346,12 +3346,12 @@ int unit_file_preset_all(
         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) {
+static UnitFileList* unit_file_list_free_one(UnitFileList *f) {
         if (!f)
-                return;
+                return NULL;
 
         free(f->path);
-        free(f);
+        return mfree(f);
 }
 
 Hashmap* unit_file_list_free(Hashmap *h) {