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

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

Console devices require 2 queues (event, status).
Example integration:
  - Added --vhost-user-console option to chroot_vm

Example usage:
On host, start vhost-device-input backend
vhost-device-input --socket-path /tmp/input.sock \
                   --event-list /dev/input/event3

In libkrun
./chroot_vm --vhost-user-input=/tmp/input.sock0 / /bin/sh

The guest will see the input device as /dev/input/event0 and
can read input events from the host device.

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

Author: Dorinda Bassey

examples/chroot_vm.c

@@ -40,6 +40,7 @@ static void print_help(char *const name)
         "              --net=NET_MODE        Set network mode\n"
         "              --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-input=PATH Use vhost-user input 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"
@@ -70,6 +71,7 @@ static const struct option long_options[] = {
     { "net_mode", required_argument, NULL, 'N' },
     { "passt-socket", required_argument, NULL, 'P' },
     { "vhost-user-rng", required_argument, NULL, 'V' },
+    { "vhost-user-input", required_argument, NULL, 'I' },
     { "vhost-user-snd", required_argument, NULL, 'S' },
     { "vhost-user-vsock", required_argument, NULL, 'K' },
     { "vhost-user-can", required_argument, NULL, 'A' },
@@ -84,6 +86,7 @@ struct cmdline {
     enum net_mode net_mode;
     char const *passt_socket_path;
     char const *vhost_user_rng_socket;
+    char const *vhost_user_input_socket;
     char const *vhost_user_snd_socket;
     char const *vhost_user_vsock_socket;
     char const *vhost_user_can_socket;
@@ -115,6 +118,7 @@ bool parse_cmdline(int argc, char *const argv[], struct cmdline *cmdline)
         .net_mode = NET_MODE_TSI,
         .passt_socket_path = NULL,
         .vhost_user_rng_socket = NULL,
+        .vhost_user_input_socket = NULL,
         .vhost_user_snd_socket = NULL,
         .vhost_user_vsock_socket = NULL,
         .vhost_user_can_socket = NULL,
@@ -157,6 +161,9 @@ bool parse_cmdline(int argc, char *const argv[], struct cmdline *cmdline)
         case 'V':
             cmdline->vhost_user_rng_socket = optarg;
             break;
+        case 'I':
+            cmdline->vhost_user_input_socket = optarg;
+            break;
         case 'S':
             cmdline->vhost_user_snd_socket = optarg;
             break;
@@ -307,6 +314,18 @@ int main(int argc, char *const argv[])
         printf("Using vhost-user RNG backend at %s (custom queue size: 512)\n", cmdline.vhost_user_rng_socket);
     }
 
+    // Configure vhost-user input if requested
+    if (cmdline.vhost_user_input_socket != NULL) {
+        if (!check_krun_error(krun_add_vhost_user_device(ctx_id, KRUN_VIRTIO_DEVICE_INPUT,
+                                                          cmdline.vhost_user_input_socket, NULL,
+                                                          KRUN_VHOST_USER_INPUT_NUM_QUEUES,
+                                                          KRUN_VHOST_USER_INPUT_QUEUE_SIZES),
+                              "Error adding vhost-user input device")) {
+            return -1;
+        }
+        printf("Using vhost-user input backend at %s\n", cmdline.vhost_user_input_socket);
+    }
+
     // Configure vhost-user sound if requested
     if (cmdline.vhost_user_snd_socket != NULL) {
         if (!check_krun_error(krun_add_vhost_user_device(ctx_id, KRUN_VIRTIO_DEVICE_SND,

include/libkrun.h

@@ -753,6 +753,7 @@ int32_t krun_set_snd_device(uint32_t ctx_id, bool enable);
  */
 #define KRUN_VIRTIO_DEVICE_CONSOLE 3
 #define KRUN_VIRTIO_DEVICE_RNG 4
+#define KRUN_VIRTIO_DEVICE_INPUT 18
 #define KRUN_VIRTIO_DEVICE_VSOCK 19
 #define KRUN_VIRTIO_DEVICE_SND 25
 #define KRUN_VIRTIO_DEVICE_CAN 36
@@ -772,6 +773,13 @@ int32_t krun_set_snd_device(uint32_t ctx_id, bool enable);
 #define KRUN_VHOST_USER_RNG_NUM_QUEUES 1
 #define KRUN_VHOST_USER_RNG_QUEUE_SIZES ((uint16_t[]){256})
 
+/**
+ * Vhost-user input device default queue configuration.
+ * Input device uses 2 queues: eventq (idx 0), statusq (idx 1).
+ */
+#define KRUN_VHOST_USER_INPUT_NUM_QUEUES 2
+#define KRUN_VHOST_USER_INPUT_QUEUE_SIZES ((uint16_t[]){1024, 1024})
+
 /**
  * Vhost-user sound device default queue configuration.
  * Sound device uses 4 queues: control (idx 0), event (idx 1), TX/playback (idx 2), RX/capture (idx 3).