hashmap: introduce hash_ops to make struct Hashmap smaller

It is redundant to store 'hash' and 'compare' function pointers in
struct Hashmap separately. The functions always comprise a pair.
Store a single pointer to struct hash_ops instead.

systemd keeps hundreds of hashmaps, so this saves a little bit of
memory.

src/network/networkd-link.c

@@ -206,7 +206,7 @@ static int link_new(Manager *manager, sd_rtnl_message *message, Link **ret) {
         if (r < 0)
                 return -ENOMEM;
 
-        r = hashmap_ensure_allocated(&manager->links, NULL, NULL);
+        r = hashmap_ensure_allocated(&manager->links, NULL);
         if (r < 0)
                 return r;
 

src/network/networkd-manager.c

@@ -115,7 +115,7 @@ int manager_new(Manager **ret) {
                         return -ENOMEM;
         }
 
-        m->netdevs = hashmap_new(string_hash_func, string_compare_func);
+        m->netdevs = hashmap_new(&string_hash_ops);
         if (!m->netdevs)
                 return -ENOMEM;
 
@@ -485,15 +485,15 @@ int manager_save(Manager *m) {
         assert(m->state_file);
 
         /* We add all NTP and DNS server to a set, to filter out duplicates */
-        dns = set_new(string_hash_func, string_compare_func);
+        dns = set_new(&string_hash_ops);
         if (!dns)
                 return -ENOMEM;
 
-        ntp = set_new(string_hash_func, string_compare_func);
+        ntp = set_new(&string_hash_ops);
         if (!ntp)
                 return -ENOMEM;
 
-        domains = set_new(string_hash_func, string_compare_func);
+        domains = set_new(&string_hash_ops);
         if (!domains)
                 return -ENOMEM;
 

src/network/networkd-network.c

@@ -63,15 +63,15 @@ static int network_load_one(Manager *manager, const char *filename) {
         LIST_HEAD_INIT(network->static_addresses);
         LIST_HEAD_INIT(network->static_routes);
 
-        network->stacked_netdevs = hashmap_new(string_hash_func, string_compare_func);
+        network->stacked_netdevs = hashmap_new(&string_hash_ops);
         if (!network->stacked_netdevs)
                 return log_oom();
 
-        network->addresses_by_section = hashmap_new(NULL, NULL);
+        network->addresses_by_section = hashmap_new(NULL);
         if (!network->addresses_by_section)
                 return log_oom();
 
-        network->routes_by_section = hashmap_new(NULL, NULL);
+        network->routes_by_section = hashmap_new(NULL);
         if (!network->routes_by_section)
                 return log_oom();
 

src/network/networkd-wait-online-link.c

@@ -34,12 +34,11 @@ int link_new(Manager *m, Link **ret, int ifindex, const char *ifname) {
         assert(m);
         assert(ifindex > 0);
 
-        r = hashmap_ensure_allocated(&m->links, NULL, NULL);
+        r = hashmap_ensure_allocated(&m->links, NULL);
         if (r < 0)
                 return r;
 
-        r = hashmap_ensure_allocated(&m->links_by_name,
-                                     string_hash_func, string_compare_func);
+        r = hashmap_ensure_allocated(&m->links_by_name, &string_hash_ops);
         if (r < 0)
                 return r;