env: Add support for callbacks to environment vars

Add support for per-variable callbacks to the "hashtable" functions.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>

!!!fix comment in callback

1 files changed, 144 insertions, 0 deletions

diff --git a/common/env_callback.c b/common/env_callback.c
new file mode 100644
index 0000000..78ca367
--- /dev/null
+++ b/common/env_callback.c
@@ -0,0 +1,144 @@
+/*
+ * (C) Copyright 2012
+ * Joe Hershberger, National Instruments, joe.hershberger@ni.com
+ *
+ * See file CREDITS for list of people who contributed to this
+ * project.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+ * MA 02111-1307 USA
+ */
+
+#include <common.h>
+#include <environment.h>
+
+#if defined(CONFIG_NEEDS_MANUAL_RELOC)
+DECLARE_GLOBAL_DATA_PTR;
+#endif
+
+/*
+ * Look up a callback function pointer by name
+ */
+struct env_clbk_tbl *find_env_callback(const char *name)
+{
+	struct env_clbk_tbl *clbkp;
+	int i;
+	int num_callbacks = ll_entry_count(struct env_clbk_tbl, env_clbk);
+
+	if (name == NULL)
+		return NULL;
+
+	/* look up the callback in the linker-list */
+	for (i = 0, clbkp = ll_entry_start(struct env_clbk_tbl, env_clbk);
+	     i < num_callbacks;
+	     i++, clbkp++) {
+		if (strcmp(name, clbkp->name) == 0)
+			return clbkp;
+	}
+
+	return NULL;
+}
+
+/*
+ * Look for a possible callback for a newly added variable
+ * This is called specifically when the variable did not exist in the hash
+ * previously, so the blanket update did not find this variable.
+ */
+void env_callback_init(ENTRY *var_entry)
+{
+	const char *var_name = var_entry->key;
+	const char *callback_list = getenv(ENV_CALLBACK_VAR);
+	char callback_name[256] = "";
+	struct env_clbk_tbl *clbkp;
+	int ret = 1;
+
+	/* 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);
+
+	/* only if not found there, look in the static list */
+	if (ret)
+		ret = env_attr_lookup(ENV_CALLBACK_LIST_STATIC, var_name,
+			callback_name);
+
+	/* if an association was found, set the callback pointer */
+	if (!ret && strlen(callback_name)) {
+		clbkp = find_env_callback(callback_name);
+		if (clbkp != NULL)
+#if defined(CONFIG_NEEDS_MANUAL_RELOC)
+			var_entry->callback = clbkp->callback + gd->reloc_off;
+#else
+			var_entry->callback = clbkp->callback;
+#endif
+	}
+}
+
+/*
+ * Called on each existing env var prior to the blanket update since removing
+ * a callback association should remove its callback.
+ */
+static int clear_callback(ENTRY *entry)
+{
+	entry->callback = NULL;
+
+	return 0;
+}
+
+/*
+ * Call for each element in the list that associates variables to callbacks
+ */
+static int set_callback(const char *name, const char *value)
+{
+	ENTRY e, *ep;
+	struct env_clbk_tbl *clbkp;
+
+	e.key	= name;
+	e.data	= NULL;
+	hsearch_r(e, FIND, &ep, &env_htab, 0);
+
+	/* does the env variable actually exist? */
+	if (ep != NULL) {
+		/* the assocaition delares no callback, so remove the pointer */
+		if (value == NULL || strlen(value) == 0)
+			ep->callback = NULL;
+		else {
+			/* assign the requested callback */
+			clbkp = find_env_callback(value);
+			if (clbkp != NULL)
+#if defined(CONFIG_NEEDS_MANUAL_RELOC)
+				ep->callback = clbkp->callback + gd->reloc_off;
+#else
+				ep->callback = clbkp->callback;
+#endif
+		}
+	}
+
+	return 0;
+}
+
+static int on_callbacks(const char *name, const char *value, enum env_op op,
+	int flags)
+{
+	/* remove all callbacks */
+	hwalk_r(&env_htab, clear_callback);
+
+	/* configure any static callback bindings */
+	env_attr_walk(ENV_CALLBACK_LIST_STATIC, set_callback);
+	/* configure any dynamic callback bindings */
+	env_attr_walk(value, set_callback);
+
+	return 0;
+}
+U_BOOT_ENV_CALLBACK(callbacks, on_callbacks);