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

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

Example integration:
- Added --vhost-user-can option to chroot_vm
- Uses 3 queues (TX, RX, control) with 64-entry queue sizes
- Follows same pattern as other vhost-user device integrations

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

Author: Dorinda Bassey

examples/chroot_vm.c

@@ -42,6 +42,7 @@ static void print_help(char *const name)
         "              --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"
+        "              --vhost-user-can=PATH Use vhost-user CAN backend at socket PATH\n"
         "NET_MODE can be either TSI (default) or PASST\n"
         "\n"
         "NEWROOT:      the root directory of the vm\n"
@@ -60,6 +61,7 @@ static const struct option long_options[] = {
     { "vhost-user-rng", required_argument, NULL, 'V' },
     { "vhost-user-snd", required_argument, NULL, 'S' },
     { "vhost-user-vsock", required_argument, NULL, 'K' },
+    { "vhost-user-can", required_argument, NULL, 'A' },
     { NULL, 0, NULL, 0 }
 };
 
@@ -72,6 +74,7 @@ struct cmdline {
     char const *vhost_user_rng_socket;
     char const *vhost_user_snd_socket;
     char const *vhost_user_vsock_socket;
+    char const *vhost_user_can_socket;
     char const *new_root;
     char *const *guest_argv;
 };
@@ -101,6 +104,7 @@ bool parse_cmdline(int argc, char *const argv[], struct cmdline *cmdline)
         .vhost_user_rng_socket = NULL,
         .vhost_user_snd_socket = NULL,
         .vhost_user_vsock_socket = NULL,
+        .vhost_user_can_socket = NULL,
         .new_root = NULL,
         .guest_argv = NULL,
         .log_target = KRUN_LOG_TARGET_DEFAULT,
@@ -145,6 +149,9 @@ bool parse_cmdline(int argc, char *const argv[], struct cmdline *cmdline)
         case 'K':
             cmdline->vhost_user_vsock_socket = optarg;
             break;
+        case 'A':
+            cmdline->vhost_user_can_socket = optarg;
+            break;
         case '?':
             return false;
         default:
@@ -317,6 +324,19 @@ int main(int argc, char *const argv[])
         printf("Using vhost-user vsock backend at %s\n", cmdline.vhost_user_vsock_socket);
     }
 
+    // Configure vhost-user CAN if requested
+    if (cmdline.vhost_user_can_socket != NULL) {
+        if (err = krun_add_vhost_user_device(ctx_id, KRUN_VIRTIO_DEVICE_CAN,
+                                              cmdline.vhost_user_can_socket, NULL,
+                                              KRUN_VHOST_USER_CAN_NUM_QUEUES,
+                                              KRUN_VHOST_USER_CAN_QUEUE_SIZES)) {
+            errno = -err;
+            perror("Error adding vhost-user CAN device");
+            return -1;
+        }
+        printf("Using vhost-user CAN backend at %s\n", cmdline.vhost_user_can_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;

include/libkrun.h

@@ -747,6 +747,13 @@ int32_t krun_set_snd_device(uint32_t ctx_id, bool enable);
 #define KRUN_VHOST_USER_VSOCK_NUM_QUEUES 3
 #define KRUN_VHOST_USER_VSOCK_QUEUE_SIZES ((uint16_t[]){128, 128, 128})
 
+/**
+ * Vhost-user CAN device default queue configuration.
+ * CAN device uses 3 queues: TX (idx 0), RX (idx 1), control (idx 2).
+ */
+#define KRUN_VHOST_USER_CAN_NUM_QUEUES 3
+#define KRUN_VHOST_USER_CAN_QUEUE_SIZES ((uint16_t[]){64, 64, 64})
+
 /**
  * Add a vhost-user device to the VM.
  *