convert string_vector_(iter(free) + reset()) to string_vector_empty()

(Reimplement libnbd commit c7ff70101e8c, "convert
string_vector_(iter(free) + reset()) to string_vector_empty()",
2023-02-28.)

Convert the 5 string_vector_(iter(free) + reset()) call sites mentioned
previously to string_vector_empty().

Note that the converted code performs more cleanup steps in some cases
than strictly necessary, but the extra work is harmless, and arguably
beneficial for clarity / consistency.

Also note that the CLEANUP_FREE_*() macros remain unique to nbdkit; libnbd
does not use __attribute__((cleanup)), per libnbd commit f306e231d294
("common/utils: Add extensible string, based on vector", 2022-03-12).

Signed-off-by: Laszlo Ersek <[email protected]>
Message-Id: <[email protected]>
Acked-by: Richard W.M. Jones <[email protected]>
Acked-by: Eric Blake <[email protected]>

common/utils/environ.c

@@ -111,7 +111,6 @@ copy_environ (char **env, ...)
   return ret.ptr;
 
  error:
-  string_vector_iter (&ret, (void *) free);
-  free (ret.ptr);
+  string_vector_empty (&ret);
   return NULL;
 }

common/utils/string-vector.h

@@ -41,13 +41,6 @@ DEFINE_POINTER_VECTOR_TYPE (string_vector, char *);
 
 /* This frees both the array and the strings. */
 #define CLEANUP_FREE_STRING_VECTOR \
-  __attribute__ ((cleanup (cleanup_free_string_vector)))
-
-static void __attribute__ ((__unused__))
-cleanup_free_string_vector (string_vector *v)
-{
-  string_vector_iter (v, (void*)free);
-  string_vector_reset (v);
-}
+  __attribute__ ((cleanup (string_vector_empty)))
 
 #endif /* STRING_VECTOR_H */

plugins/iso/iso.c

@@ -128,8 +128,7 @@ make_iso (void)
 static void
 iso_unload (void)
 {
-  string_vector_iter (&dirs, (void *) free);
-  free (dirs.ptr);
+  string_vector_empty (&dirs);
 
   if (fd >= 0)
     close (fd);

plugins/split/split.c

@@ -64,8 +64,7 @@ static pthread_mutex_t lseek_lock = PTHREAD_MUTEX_INITIALIZER;
 static void
 split_unload (void)
 {
-  string_vector_iter (&filenames, (void *) free);
-  free (filenames.ptr);
+  string_vector_empty (&filenames);
 }
 
 static int

server/public.c

@@ -1013,8 +1013,7 @@ free_interns (void)
   struct connection *conn = threadlocal_get_conn ();
   string_vector *list = conn ? &conn->interns : &global_interns;
 
-  string_vector_iter (list, (void *) free);
-  string_vector_reset (list);
+  string_vector_empty (list);
 }
 
 static const char *