console: check parameter mutual exclusivity

- Introduce `InvalidCmdlineOption` error type to handle conflicting parameters
- Implement backend-specific parameter checks:
  * Nested backend:
    - Require single socket (socket_count=1)
    - Disallow TCP port/UDS path
  * Network backend: Disallow UDS path
  * UDS backend: Disallow TCP port
- Remove default TCP port value to enforce explicit configuration

Signed-off-by: Hang SU <[email protected]>

Author: Hang SU

vhost-device-console/src/backend.rs

@@ -42,6 +42,8 @@ pub enum Error {
     ThreadPanic(String, Box<dyn Any + Send>),
     #[error("Error using multiple sockets with Nested backend")]
     WrongBackendSocket,
+    #[error("Invalid cmdline option")]
+    InvalidCmdlineOption,
     #[error("Invalid uds file")]
     InvalidUdsFile,
 }

vhost-device-console/src/main.rs

@@ -70,7 +70,7 @@ struct ConsoleArgs {
     /// Initial tcp port to be used with `network` backend. If socket_count is
     /// `N` then the following tcp ports will be created: `tcp_port`,
     /// `tcp_port + 1`, ... , `tcp_port + (N - 1)`.
-    #[clap(short = 'p', long, value_name = "PORT", default_value = "12345")]
+    #[clap(short = 'p', long, value_name = "PORT")]
     tcp_port: String,
 
     /// Specify the maximum size of virtqueue, the default is 128.
@@ -86,8 +86,22 @@ impl TryFrom<ConsoleArgs> for VuConsoleConfig {
             return Err(Error::SocketCountInvalid(0));
         }
 
-        if (args.backend == BackendType::Nested) && (args.socket_count != 1) {
-            return Err(Error::WrongBackendSocket);
+        if args.backend == BackendType::Nested {
+            if args.socket_count != 1 {
+                return Err(Error::WrongBackendSocket);
+            }
+
+            if (!args.tcp_port.is_empty()) || (args.uds_path.is_some()) {
+                return Err(Error::InvalidCmdlineOption);
+            }
+        }
+
+        if args.backend == BackendType::Network && args.uds_path.is_some() {
+            return Err(Error::InvalidCmdlineOption);
+        }
+
+        if args.backend == BackendType::Uds && !args.tcp_port.is_empty() {
+            return Err(Error::InvalidCmdlineOption);
         }
 
         let ConsoleArgs {