When a server closes the connection after a successful handshake but before running any operations, the channel returned by nbd_co_establish_connection() is the closed one and the connect thread is not started.
When configured with reconnect-delay=0 (the default), this situation generates at least two IO errors. The first one happens when trying to issue an operation to the closed socket. The connect thread will be started on the next request, which may happen long after, and will create the second error as nbd_co_establish_connection() returns a NULL channel. Peeking the channel to detect FIN or RST avoids the first IO error and does not delay the starting of the connect thread. Signed-off-by: Guillaume Vincke <[email protected]> --- nbd/client-connection.c | 35 +++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) diff --git a/nbd/client-connection.c b/nbd/client-connection.c index 6a4f080717..878219fede 100644 --- a/nbd/client-connection.c +++ b/nbd/client-connection.c @@ -274,6 +274,26 @@ void nbd_client_connection_release(NBDClientConnection *conn) } } +/* only true when the peer closed the channel. Does not detect if dead */ +static bool nbd_channel_is_closed(QIOChannel *ioc) +{ + char data; + struct iovec iov = { .iov_base = &data, .iov_len = 1 }; + ssize_t len = -1; + + if (!qio_channel_has_feature(ioc, QIO_CHANNEL_FEATURE_READ_MSG_PEEK)) { + return false; + } + + len = qio_channel_readv_full( + ioc, &iov, 1, NULL, NULL, QIO_CHANNEL_READ_FLAG_MSG_PEEK, NULL); + + if (len == 0 || (len < 0 && len != QIO_CHANNEL_ERR_BLOCK)) { + return true; + } + return false; +} + /* * Get a new connection in context of @conn: * if the thread is running, wait for completion @@ -295,6 +315,7 @@ nbd_co_establish_connection(NBDClientConnection *conn, NBDExportInfo *info, bool blocking, Error **errp) { QemuThread thread; + QIOChannel *ioc; if (conn->do_negotiation) { assert(info); @@ -308,6 +329,20 @@ nbd_co_establish_connection(NBDClientConnection *conn, NBDExportInfo *info, assert(!conn->wait_co); if (!conn->running) { + if (conn->sioc) { + /* discard if the socket got closed by its peer */ + ioc = QIO_CHANNEL(conn->sioc); + if (!qio_channel_set_blocking(ioc, false, NULL) || + nbd_channel_is_closed(ioc)) { + + qio_channel_close(ioc, NULL); + object_unref(OBJECT(conn->sioc)); + conn->sioc = NULL; + object_unref(OBJECT(conn->ioc)); + conn->ioc = NULL; + } + } + if (conn->sioc) { /* Previous attempt finally succeeded in background */ if (conn->do_negotiation) { -- 2.43.0
