xenstore: Make sure that libxs reports an error if xenstored drops

the connection, rather than getting stuck forever.

Patch from: Steven Smith <steven.smith@eu.citrix.com>
Signed-off-by: Tim Deegan <Tim.Deegan@citrix.com>

1 files changed, 33 insertions, 3 deletions

diff --git a/tools/xenstore/xs.c b/tools/xenstore/xs.c
index 7e3d9c4b63..094db25efa 100644
--- a/tools/xenstore/xs.c
+++ b/tools/xenstore/xs.c
@@ -94,6 +94,8 @@ struct xs_handle {
  */
 #define cleanup_pop(run)        ((void)0); pthread_cleanup_pop(run)
 
+#define read_thread_exists(h)	(h->read_thr_exists)
+
 static void *read_thread(void *arg);
 
 #else /* !defined(USE_PTHREAD) */
@@ -112,6 +114,7 @@ struct xs_handle {
 #define condvar_wait(c,m,hnd)	read_message(hnd)
 #define cleanup_push(f, a)	((void)0)
 #define cleanup_pop(run)	((void)0)
+#define read_thread_exists(h)	(0)
 
 #endif
 
@@ -330,16 +333,25 @@ static void *read_reply(
 {
 	struct xs_stored_msg *msg;
 	char *body;
+	int read_from_thread;
+
+	read_from_thread = read_thread_exists(h);
 
 #ifdef USE_PTHREAD
 	/* Read from comms channel ourselves if there is no reader thread. */
-	if (!h->read_thr_exists && (read_message(h) == -1))
+	if (!read_from_thread && (read_message(h) == -1))
 		return NULL;
 #endif
 
 	mutex_lock(&h->reply_mutex);
-	while (list_empty(&h->reply_list))
+	while (list_empty(&h->reply_list) && (!read_from_thread || read_thread_exists(h)))
 		condvar_wait(&h->reply_condvar, &h->reply_mutex, h);
+	if (read_from_thread && !read_thread_exists(h)) {
+		mutex_unlock(&h->reply_mutex);
+		errno = EINVAL;
+		return NULL;
+	}
+	assert(!list_empty(&h->reply_list));
 	msg = list_top(&h->reply_list, struct xs_stored_msg, list);
 	list_del(&msg->list);
 	assert(list_empty(&h->reply_list));
@@ -647,8 +659,13 @@ char **xs_read_watch(struct xs_handle *h, unsigned int *num)
 	mutex_lock(&h->watch_mutex);
 
 	/* Wait on the condition variable for a watch to fire. */
-	while (list_empty(&h->watch_list))
+	while (list_empty(&h->watch_list) && read_thread_exists(h))
 		condvar_wait(&h->watch_condvar, &h->watch_mutex, h);
+	if (!read_thread_exists(h)) {
+		mutex_unlock(&h->watch_mutex);
+		errno = EINVAL;
+		return NULL;
+	}
 	msg = list_top(&h->watch_list, struct xs_stored_msg, list);
 	list_del(&msg->list);
 
@@ -944,6 +961,19 @@ static void *read_thread(void *arg)
 	while (read_message(h) != -1)
 		continue;
 
+	/* Kick anyone waiting for a reply */
+	pthread_mutex_lock(&h->request_mutex);
+	h->read_thr_exists = 0;
+	pthread_mutex_unlock(&h->request_mutex);
+
+	pthread_mutex_lock(&h->reply_mutex);
+	pthread_cond_signal(&h->reply_condvar);
+	pthread_mutex_unlock(&h->reply_mutex);
+
+	pthread_mutex_lock(&h->watch_mutex);
+	pthread_cond_signal(&h->watch_condvar);
+	pthread_mutex_unlock(&h->watch_mutex);
+
 	return NULL;
 }
 #endif