Give a hint about missing kernel config CONFIG_VFIO_DEVICE_CDEV.

Reviewed-by: Yi Liu <yi.l.liu@intel.com>
Reviewed-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
---
 hw/vfio/iommufd.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/hw/vfio/iommufd.c b/hw/vfio/iommufd.c
index 131612eb836..3e33dfbb356 100644
--- a/hw/vfio/iommufd.c
+++ b/hw/vfio/iommufd.c
@@ -274,7 +274,10 @@ static int iommufd_cdev_getfd(const char *sysfs_path, Error **errp)
     }
 
     if (!g_file_get_contents(vfio_dev_path, &contents, &length, NULL)) {
-        error_setg(errp, "failed to load \"%s\"", vfio_dev_path);
+        error_setg(errp,
+                   "failed to load \"%s\""
+                   " (is your kernel config missing CONFIG_VFIO_DEVICE_CDEV?)",
+                   vfio_dev_path);
         goto out_close_dir;
     }
 
-- 
2.47.3