make env_entry::callback conditional on !CONFIG_SPL_BUILD

The callback member of struct env_entry is always NULL for an SPL
build. Removing it thus saves a bit of run-time memory in the
SPL (when CONFIG_SPL_ENV_SUPPORT=y) since struct env_entry is embedded
in struct env_entry_node - i.e. about 2KB for the normal case of
512+change hash table entries.

Two small fixups are needed for this, all other references to the
callback member are already under !CONFIG_SPL_BUILD: Don't initialize
.callback in set_flags() - hsearch_r doesn't use that value
anyway. And make env_callback_init() initialize ->callback to NULL for
a new entry instead of relying on an unused or deleted entry having
NULL in ->callback.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Reviewed-by: Simon Glass <sjg@chromium.org>

env/callback.c

@@ -55,6 +55,8 @@ void env_callback_init(struct env_entry *var_entry)
 		first_call = 0;
 	}
 
+	var_entry->callback = NULL;
+
 	/* look in the ".callbacks" var for a reference to this variable */
 	if (callback_list != NULL)
 		ret = env_attr_lookup(callback_list, var_name, callback_name);

env/flags.c

@@ -457,7 +457,6 @@ static int set_flags(const char *name, const char *value, void *priv)
 
 	e.key	= name;
 	e.data	= NULL;
-	e.callback = NULL;
 	hsearch_r(e, ENV_FIND, &ep, &env_htab, 0);
 
 	/* does the env variable actually exist? */

include/search.h

@@ -29,8 +29,10 @@ enum env_action {
 struct env_entry {
 	const char *key;
 	char *data;
+#ifndef CONFIG_SPL_BUILD
 	int (*callback)(const char *name, const char *value, enum env_op op,
 		int flags);
+#endif
 	int flags;
 };
 

lib/hashtable.c

@@ -450,7 +450,6 @@ static void _hdelete(const char *key, struct hsearch_data *htab,
 	debug("hdelete: DELETING key \"%s\"\n", key);
 	free((void *)ep->key);
 	free(ep->data);
-	ep->callback = NULL;
 	ep->flags = 0;
 	htab->table[idx].used = USED_DELETED;