ifupdown: code to deconstruct the state_list gracefully

(patch by Gabriel L. Somlo <somlo@cmu.edu>)

include/libbb.h

@@ -475,6 +475,7 @@ typedef struct llist_s {
 extern void llist_add_to(llist_t **old_head, void *data);
 extern void llist_add_to_end(llist_t **list_head, void *data);
 extern void *llist_pop(llist_t **elm);
+extern void llist_unlink(llist_t **head, llist_t *elm);
 extern void llist_free(llist_t *elm, void (*freeit)(void *data));
 extern llist_t* llist_rev(llist_t *list);
 

libbb/llist.c

@@ -45,21 +45,40 @@ void llist_add_to_end(llist_t ** list_head, void *data)
 /* Remove first element from the list and return it */
 void *llist_pop(llist_t ** head)
 {
-	void *data;
+	void *data, *next;
 
 	if (!*head)
-		data = *head;
-	else {
-		void *next = (*head)->link;
+		return NULL;
 
-		data = (*head)->data;
-		free(*head);
-		*head = next;
-	}
+	data = (*head)->data;
+	next = (*head)->link;
+	free(*head);
+	*head = next;
 
 	return data;
 }
 
+/* Unlink arbitrary given element from the list */
+void llist_unlink(llist_t **head, llist_t *elm)
+{
+	llist_t *crt;
+
+	if (!(elm && *head))
+		return;
+
+	if (elm == *head) {
+		*head = (*head)->link;
+		return;
+	}
+
+	for (crt = *head; crt; crt = crt->link) {
+		if (crt->link == elm) {
+			crt->link = elm->link;
+			return;
+		}
+	}
+}
+
 /* Recursively free all elements in the linked list.  If freeit != NULL
  * call it on each datum in the list */
 void llist_free(llist_t * elm, void (*freeit) (void *data))

networking/ifupdown.c

@@ -1091,6 +1091,7 @@ int ifupdown_main(int argc, char **argv)
 	llist_t *state_list = NULL;
 	llist_t *target_list = NULL;
 	const char *interfaces = "/etc/network/interfaces";
+	FILE *state_fp;
 	int any_failures = 0;
 
 	cmds = iface_down;
@@ -1117,6 +1118,19 @@ int ifupdown_main(int argc, char **argv)
 	startup_PATH = getenv("PATH");
 	if (!startup_PATH) startup_PATH = "";
 
+	/* Read the previous state from the state file */
+	state_fp = fopen_or_warn("/var/run/ifstate", "r");
+	if (state_fp) {
+		char *start, *end_ptr;
+		while ((start = xmalloc_fgets(state_fp)) != NULL) {
+			/* We should only need to check for a single character */
+			end_ptr = start + strcspn(start, " \t\n");
+			*end_ptr = '\0';
+			llist_add_to(&state_list, start);
+		}
+		fclose(state_fp);
+	}
+
 	/* Create a list of interfaces to work on */
 	if (DO_ALL) {
 		if (cmds == iface_up) {
@@ -1166,7 +1180,7 @@ int ifupdown_main(int argc, char **argv)
 				}
 			} else {
 				/* ifdown */
-				if (iface_state) {
+				if (!iface_state) {
 					bb_error_msg("interface %s not configured", iface);
 					continue;
 				}
@@ -1236,7 +1250,8 @@ int ifupdown_main(int argc, char **argv)
 					iface_state->data = newiface;
 				}
 			} else {
-				/* Remove an interface from the linked list */
+				/* Remove an interface from state_list */
+				llist_unlink(&state_list, iface_state);
 				free(llist_pop(&iface_state));
 			}
 		}
@@ -1244,8 +1259,6 @@ int ifupdown_main(int argc, char **argv)
 
 	/* Actually write the new state */
 	if (!NO_ACT) {
-		FILE *state_fp;
-
 		state_fp = xfopen("/var/run/ifstate", "w");
 		while (state_list) {
 			if (state_list->data) {