Pass server->client command over a separate socket pair (#762)

Use separate socket for server->client commands

This change adds support for a separate socket to carry commands in the
server-to-client direction. It has proven problematic to send commands
in both directions over a single socket, since matching replies to
commands can become non-trivial when both sides send commands at the same
time and adds significant complexity. See issue #279 for details.

To set up the reverse communication channel, the client indicates
support for it via a new capability flag in the version message. The
server will then create a fresh pair of sockets and pass one end to the
client in its version reply. When the server wishes to send commands to
the client at a later point, it now uses its end of the new socket pair
rather than the main socket. Corresponding replies are also passed back
over the new socket pair.

Signed-off-by: Mattias Nissler <mnissler@rivosinc.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/samples/client.c b/samples/client.c
index 0086fd6..ed66a30 100644
--- a/samples/client.c
+++ b/samples/client.c
@@ -197,7 +197,7 @@ recv_version(int sock, int *server_max_fds, size_t *server_max_data_xfer_size,
         }
 
         ret = tran_parse_version_json(json_str, server_max_fds,
-                                      server_max_data_xfer_size, pgsize);
+                                      server_max_data_xfer_size, pgsize, NULL);
 
         if (ret < 0) {
             err(EXIT_FAILURE, "failed to parse server JSON \"%s\"", json_str);