libkrun: Add API constants and example for vhost-user vsock

Add public API constants for vhost-user vsock devices and example
usage in chroot_vm. The underlying support already exists via the
generic VhostUserDevice wrapper.

Example integration:
- Added --vhost-user-vsock option to chroot_vm
- Calls krun_disable_implicit_vsock() to avoid conflict with
  built-in device
- Skips TSI port mapping when vhost-user-vsock is active

Signed-off-by: Dorinda Bassey <dbassey@redhat.com>

Author: Dorinda Bassey

examples/chroot_vm.c

@@ -41,6 +41,7 @@ static void print_help(char *const name)
         "              --passt-socket=PATH   Instead of starting passt, connect to passt socket at PATH\n"
         "              --vhost-user-rng=PATH Use vhost-user RNG backend at socket PATH\n"
         "              --vhost-user-snd=PATH Use vhost-user sound backend at socket PATH\n"
+        "              --vhost-user-vsock=PATH Use vhost-user vsock backend at socket PATH\n"
         "NET_MODE can be either TSI (default) or PASST\n"
         "\n"
         "NEWROOT:      the root directory of the vm\n"
@@ -68,6 +69,7 @@ static const struct option long_options[] = {
     { "passt-socket", required_argument, NULL, 'P' },
     { "vhost-user-rng", required_argument, NULL, 'V' },
     { "vhost-user-snd", required_argument, NULL, 'S' },
+    { "vhost-user-vsock", required_argument, NULL, 'K' },
     { NULL, 0, NULL, 0 }
 };
 
@@ -79,6 +81,7 @@ struct cmdline {
     char const *passt_socket_path;
     char const *vhost_user_rng_socket;
     char const *vhost_user_snd_socket;
+    char const *vhost_user_vsock_socket;
     char const *new_root;
     char *const *guest_argv;
 };
@@ -107,6 +110,7 @@ bool parse_cmdline(int argc, char *const argv[], struct cmdline *cmdline)
         .passt_socket_path = NULL,
         .vhost_user_rng_socket = NULL,
         .vhost_user_snd_socket = NULL,
+        .vhost_user_vsock_socket = NULL,
         .new_root = NULL,
         .guest_argv = NULL,
         .log_target = KRUN_LOG_TARGET_DEFAULT,
@@ -148,6 +152,9 @@ bool parse_cmdline(int argc, char *const argv[], struct cmdline *cmdline)
         case 'S':
             cmdline->vhost_user_snd_socket = optarg;
             break;
+        case 'K':
+            cmdline->vhost_user_vsock_socket = optarg;
+            break;
         case '?':
             return false;
         default:
@@ -298,6 +305,24 @@ int main(int argc, char *const argv[])
         printf("Using vhost-user sound backend at %s\n", cmdline.vhost_user_snd_socket);
     }
 
+    // Configure vhost-user vsock if requested
+    if (cmdline.vhost_user_vsock_socket != NULL) {
+        // Disable the implicit vsock device to avoid conflict
+        if (!check_krun_error(krun_disable_implicit_vsock(ctx_id),
+                              "Error disabling implicit vsock")) {
+            return -1;
+        }
+
+        if (!check_krun_error(krun_add_vhost_user_device(ctx_id, KRUN_VIRTIO_DEVICE_VSOCK,
+                                                          cmdline.vhost_user_vsock_socket, NULL,
+                                                          KRUN_VHOST_USER_VSOCK_NUM_QUEUES,
+                                                          KRUN_VHOST_USER_VSOCK_QUEUE_SIZES),
+                              "Error adding vhost-user vsock device")) {
+            return -1;
+        }
+        printf("Using vhost-user vsock backend at %s\n", cmdline.vhost_user_vsock_socket);
+    }
+
     // Raise RLIMIT_NOFILE to the maximum allowed to create some room for virtio-fs
     getrlimit(RLIMIT_NOFILE, &rlim);
     rlim.rlim_cur = rlim.rlim_max;
@@ -318,7 +343,8 @@ int main(int argc, char *const argv[])
     }
 
     // Map port 18000 in the host to 8000 in the guest (if networking uses TSI)
-    if (cmdline.net_mode == NET_MODE_TSI) {
+    // Skip port mapping when using vhost-user-vsock (TSI requires built-in vsock)
+    if (cmdline.net_mode == NET_MODE_TSI && cmdline.vhost_user_vsock_socket == NULL) {
         if (err = krun_set_port_map(ctx_id, &port_map[0])) {
             errno = -err;
             perror("Error configuring port map");

include/libkrun.h

@@ -752,6 +752,7 @@ int32_t krun_set_snd_device(uint32_t ctx_id, bool enable);
  * These correspond to virtio device type IDs for devices.
  */
 #define KRUN_VIRTIO_DEVICE_RNG 4
+#define KRUN_VIRTIO_DEVICE_VSOCK 19
 #define KRUN_VIRTIO_DEVICE_SND 25
 #define KRUN_VIRTIO_DEVICE_CAN 36
 
@@ -769,6 +770,13 @@ int32_t krun_set_snd_device(uint32_t ctx_id, bool enable);
 #define KRUN_VHOST_USER_SND_NUM_QUEUES 4
 #define KRUN_VHOST_USER_SND_QUEUE_SIZES ((uint16_t[]){64, 64, 64, 64})
 
+/**
+ * Vhost-user vsock device default queue configuration.
+ * Vsock device uses 3 queues: RX (idx 0), TX (idx 1), event (idx 2).
+ */
+#define KRUN_VHOST_USER_VSOCK_NUM_QUEUES 3
+#define KRUN_VHOST_USER_VSOCK_QUEUE_SIZES ((uint16_t[]){128, 128, 128})
+
 /**
  * Add a vhost-user device to the VM.
  *