tty: flush pending data when fd is ready

if there was any data already received, make sure it is flushed to the
tty as soon as it is opened.

Closes: containers/podman#4397

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

src/conn_sock.c

@@ -180,8 +180,7 @@ static gboolean read_conn_sock(struct conn_sock_s *sock)
 
 	/* Not everything was written to stdin, let's wait for the fd to be ready.  */
 	if (sock->remaining)
-		g_unix_fd_add(masterfd_stdin, G_IO_OUT, masterfd_write_cb, NULL);
-
+		schedule_master_stdin_write();
 	return G_SOURCE_CONTINUE;
 }
 
@@ -240,7 +239,7 @@ static void write_to_masterfd_stdin(gpointer data, gpointer user_data)
 
 static void sock_try_write_to_masterfd_stdin(struct conn_sock_s *sock)
 {
-	if (!sock->remaining)
+	if (!sock->remaining || masterfd_stdin < 0)
 		return;
 
 	ssize_t w = write(masterfd_stdin, sock->buf + sock->off, sock->remaining);
@@ -264,3 +263,8 @@ static gboolean masterfd_write_cb(G_GNUC_UNUSED int fd, G_GNUC_UNUSED GIOConditi
 		return G_SOURCE_CONTINUE;
 	return G_SOURCE_REMOVE;
 }
+
+void schedule_master_stdin_write()
+{
+	g_unix_fd_add(masterfd_stdin, G_IO_OUT, masterfd_write_cb, NULL);
+}

src/conn_sock.h

@@ -18,5 +18,6 @@ struct conn_sock_s {
 char *setup_console_socket(void);
 char *setup_attach_socket(void);
 void conn_sock_shutdown(struct conn_sock_s *sock, int how);
+void schedule_master_stdin_write();
 
 #endif // CONN_SOCK_H

src/ctrl.c

@@ -5,6 +5,7 @@
 #include "globals.h"
 #include "config.h"
 #include "ctr_logging.h"
+#include "conn_sock.h"
 #include "cmsg.h"
 #include "cli.h" // opt_bundle_path
 
@@ -59,6 +60,8 @@ gboolean terminal_accept_cb(int fd, G_GNUC_UNUSED GIOCondition condition, G_GNUC
 	masterfd_stdin = console.fd;
 	masterfd_stdout = console.fd;
 
+	schedule_master_stdin_write();
+
 	/* now that we've set masterfd_stdout, we can register the ctrl_winsz_cb
 	 * if we didn't set it here, we'd risk attempting to run ioctl on
 	 * a negative fd, and fail to resize the window */