In case current kernel does not support /dev/iommu, qemu will probably
fail first because /sys/bus/pci/devices/*/vfio-dev/ is not present,
since QEMU opens it before /dev/iommu.

Instead, report an error directly when completing an iommufd object, to
inform user that kernel does not support it, with a hint about missing
CONFIG_IOMMUFD. We can't do this from initialize as there is no way to
return an error, and we don't want to abort at this step.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
---
 backends/iommufd.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/backends/iommufd.c b/backends/iommufd.c
index acfab907c03..e1fee16acf2 100644
--- a/backends/iommufd.c
+++ b/backends/iommufd.c
@@ -82,6 +82,9 @@ static void iommufd_backend_complete(UserCreatable *uc, Error **errp)
         } else {
             cpr_save_fd(name, 0, be->fd);
         }
+    } else if (!g_file_test("/dev/iommu", G_FILE_TEST_EXISTS)) {
+        error_setg(errp, "/dev/iommu does not exist"
+                         " (is your kernel config missing CONFIG_IOMMUFD?)");
     }
 }
 
-- 
2.47.3

>-----Original Message-----
>From: Pierrick Bouvier <pierrick.bouvier@linaro.org>
>Subject: [PATCH v3 1/2] backends/iommufd.c: report error when /dev/iommu is
>not available
>
>In case current kernel does not support /dev/iommu, qemu will probably
>fail first because /sys/bus/pci/devices/*/vfio-dev/ is not present,
>since QEMU opens it before /dev/iommu.
>
>Instead, report an error directly when completing an iommufd object, to
>inform user that kernel does not support it, with a hint about missing
>CONFIG_IOMMUFD. We can't do this from initialize as there is no way to
>return an error, and we don't want to abort at this step.
>
>Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
>Reviewed-by: Cédric Le Goater <clg@redhat.com>
>Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>

Reviewed-by: Zhenzhong Duan <zhenzhong.duan@intel.com>

Zhenzhong