1 files changed, 28 insertions, 3 deletions

diff --git a/lib/tran_sock.c b/lib/tran_sock.c
index 3f4c8c3..8a652c7 100644
--- a/lib/tran_sock.c
+++ b/lib/tran_sock.c
@@ -46,6 +46,7 @@
 typedef struct {
     int listen_fd;
     int conn_fd;
+    int client_cmd_socket_fd;
 } tran_sock_t;
 
 int
@@ -380,6 +381,7 @@ tran_sock_init(vfu_ctx_t *vfu_ctx)
 
     ts->listen_fd = -1;
     ts->conn_fd = -1;
+    ts->client_cmd_socket_fd = -1;
 
     if ((ts->listen_fd = socket(AF_UNIX, SOCK_STREAM, 0)) == -1) {
         ret = errno;
@@ -464,7 +466,7 @@ tran_sock_attach(vfu_ctx_t *vfu_ctx)
         return -1;
     }
 
-    ret = tran_negotiate(vfu_ctx);
+    ret = tran_negotiate(vfu_ctx, &ts->client_cmd_socket_fd);
     if (ret < 0) {
         close_safely(&ts->conn_fd);
         return -1;
@@ -607,6 +609,21 @@ tran_sock_reply(vfu_ctx_t *vfu_ctx, vfu_msg_t *msg, int err)
     return ret;
 }
 
+static void maybe_print_cmd_collision_warning(vfu_ctx_t *vfu_ctx) {
+    static bool warning_printed = false;
+    static const char *warning_msg =
+        "You are using libvfio-user in a configuration that issues "
+        "client-to-server commands, but without the twin_socket feature "
+        "enabled. This is known to break when client and server send a command "
+        "at the same time. See "
+        "https://github.com/nutanix/libvfio-user/issues/279 for details.";
+
+    if (!warning_printed) {
+        vfu_log(vfu_ctx, LOG_WARNING, "%s", warning_msg);
+        warning_printed = true;
+    }
+}
+
 static int
 tran_sock_send_msg(vfu_ctx_t *vfu_ctx, uint16_t msg_id,
               enum vfio_user_command cmd,
@@ -615,14 +632,21 @@ tran_sock_send_msg(vfu_ctx_t *vfu_ctx, uint16_t msg_id,
               void *recv_data, size_t recv_len)
 {
     tran_sock_t *ts;
+    int fd;
 
     assert(vfu_ctx != NULL);
     assert(vfu_ctx->tran_data != NULL);
 
     ts = vfu_ctx->tran_data;
 
-    return tran_sock_msg(ts->conn_fd, msg_id, cmd, send_data, send_len,
-                         hdr, recv_data, recv_len);
+    fd = ts->client_cmd_socket_fd;
+    if (fd == -1) {
+        maybe_print_cmd_collision_warning(vfu_ctx);
+        fd = ts->conn_fd;
+    }
+
+    return tran_sock_msg(fd, msg_id, cmd, send_data, send_len, hdr, recv_data,
+                         recv_len);
 }
 
 static void
@@ -636,6 +660,7 @@ tran_sock_detach(vfu_ctx_t *vfu_ctx)
 
     if (ts != NULL) {
         close_safely(&ts->conn_fd);
+        close_safely(&ts->client_cmd_socket_fd);
     }
 }