[PATCH v3 17/33] nbd/client-connection: implement connection retry

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

Add an option for thread to retry connection until success. We'll use
nbd/client-connection both for reconnect and for initial connection in
nbd_open(), so we need a possibility to use same NBDClientConnection
instance to connect once in nbd_open() and then use retry semantics for
reconnect.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 include/block/nbd.h     |  2 ++
 nbd/client-connection.c | 55 +++++++++++++++++++++++++++++------------
 2 files changed, 41 insertions(+), 16 deletions(-)

diff --git a/include/block/nbd.h b/include/block/nbd.h
index 5d86e6a393..5bb54d831c 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -409,6 +409,8 @@ const char *nbd_err_lookup(int err);
 /* nbd/client-connection.c */
 typedef struct NBDClientConnection NBDClientConnection;
 
+void nbd_client_connection_enable_retry(NBDClientConnection *conn);
+
 NBDClientConnection *nbd_client_connection_new(const SocketAddress *saddr,
                                                bool do_negotiation,
                                                const char *export_name,
diff --git a/nbd/client-connection.c b/nbd/client-connection.c
index ae4a77f826..002bd91f42 100644
--- a/nbd/client-connection.c
+++ b/nbd/client-connection.c
@@ -36,6 +36,8 @@ struct NBDClientConnection {
     NBDExportInfo initial_info;
     bool do_negotiation;
 
+    bool do_retry;
+
     /*
      * Result of last attempt. Valid in FAIL and SUCCESS states.
      * If you want to steal error, don't forget to set pointer to NULL.
@@ -52,6 +54,15 @@ struct NBDClientConnection {
     Coroutine *wait_co; /* nbd_co_establish_connection() wait in yield() */
 };
 
+/*
+ * The function isn't protected by any mutex, so call it when thread is not
+ * running.
+ */
+void nbd_client_connection_enable_retry(NBDClientConnection *conn)
+{
+    conn->do_retry = true;
+}
+
 NBDClientConnection *nbd_client_connection_new(const SocketAddress *saddr,
                                                bool do_negotiation,
                                                const char *export_name,
@@ -144,24 +155,37 @@ static void *connect_thread_func(void *opaque)
     NBDClientConnection *conn = opaque;
     bool do_free;
     int ret;
+    uint64_t timeout = 1;
+    uint64_t max_timeout = 16;
+
+    while (true) {
+        conn->sioc = qio_channel_socket_new();
+
+        error_free(conn->err);
+        conn->err = NULL;
+        conn->updated_info = conn->initial_info;
+
+        ret = nbd_connect(conn->sioc, conn->saddr,
+                          conn->do_negotiation ? &conn->updated_info : NULL,
+                          conn->tlscreds, &conn->ioc, &conn->err);
+        conn->updated_info.x_dirty_bitmap = NULL;
+        conn->updated_info.name = NULL;
+
+        if (ret < 0) {
+            object_unref(OBJECT(conn->sioc));
+            conn->sioc = NULL;
+            if (conn->do_retry) {
+                sleep(timeout);
+                if (timeout < max_timeout) {
+                    timeout *= 2;
+                }
+                continue;
+            }
+        }
 
-    conn->sioc = qio_channel_socket_new();
-
-    error_free(conn->err);
-    conn->err = NULL;
-    conn->updated_info = conn->initial_info;
-
-    ret = nbd_connect(conn->sioc, conn->saddr,
-                      conn->do_negotiation ? &conn->updated_info : NULL,
-                      conn->tlscreds, &conn->ioc, &conn->err);
-    if (ret < 0) {
-        object_unref(OBJECT(conn->sioc));
-        conn->sioc = NULL;
+        break;
     }
 
-    conn->updated_info.x_dirty_bitmap = NULL;
-    conn->updated_info.name = NULL;
-
     WITH_QEMU_LOCK_GUARD(&conn->mutex) {
         assert(conn->running);
         conn->running = false;
@@ -172,7 +196,6 @@ static void *connect_thread_func(void *opaque)
         do_free = conn->detached;
     }
 
-
     if (do_free) {
         nbd_client_connection_do_free(conn);
     }
-- 
2.29.2