vfio/pci: Extract mdev check into an helper

In preparation to skip initialization of the HostIOMMUDevice for mdev,
extract the checks that validate if a device is an mdev into helpers.

A vfio_device_is_mdev() is created, and subsystems consult VFIODevice::mdev
to check if it's mdev or not.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>

hw/vfio/helpers.c

@@ -675,3 +675,17 @@ int vfio_device_get_aw_bits(VFIODevice *vdev)
 
     return HOST_IOMMU_DEVICE_CAP_AW_BITS_MAX;
 }
+
+bool vfio_device_is_mdev(VFIODevice *vbasedev)
+{
+    g_autofree char *subsys = NULL;
+    g_autofree char *tmp = NULL;
+
+    if (!vbasedev->sysfsdev) {
+        return false;
+    }
+
+    tmp = g_strdup_printf("%s/subsystem", vbasedev->sysfsdev);
+    subsys = realpath(tmp, NULL);
+    return subsys && (strcmp(subsys, "/sys/bus/mdev") == 0);
+}

hw/vfio/pci.c

@@ -2963,12 +2963,9 @@ static void vfio_realize(PCIDevice *pdev, Error **errp)
     ERRP_GUARD();
     VFIOPCIDevice *vdev = VFIO_PCI(pdev);
     VFIODevice *vbasedev = &vdev->vbasedev;
-    char *subsys;
     int i, ret;
-    bool is_mdev;
     char uuid[UUID_STR_LEN];
     g_autofree char *name = NULL;
-    g_autofree char *tmp = NULL;
 
     if (vbasedev->fd < 0 && !vbasedev->sysfsdev) {
         if (!(~vdev->host.domain || ~vdev->host.bus ||
@@ -2997,14 +2994,11 @@ static void vfio_realize(PCIDevice *pdev, Error **errp)
      * stays in sync with the active working set of the guest driver.  Prevent
      * the x-balloon-allowed option unless this is minimally an mdev device.
      */
-    tmp = g_strdup_printf("%s/subsystem", vbasedev->sysfsdev);
-    subsys = realpath(tmp, NULL);
-    is_mdev = subsys && (strcmp(subsys, "/sys/bus/mdev") == 0);
-    free(subsys);
+    vbasedev->mdev = vfio_device_is_mdev(vbasedev);
 
-    trace_vfio_mdev(vbasedev->name, is_mdev);
+    trace_vfio_mdev(vbasedev->name, vbasedev->mdev);
 
-    if (vbasedev->ram_block_discard_allowed && !is_mdev) {
+    if (vbasedev->ram_block_discard_allowed && !vbasedev->mdev) {
         error_setg(errp, "x-balloon-allowed only potentially compatible "
                    "with mdev devices");
         goto error;

include/hw/vfio/vfio-common.h

@@ -116,6 +116,7 @@ typedef struct VFIODevice {
     DeviceState *dev;
     int fd;
     int type;
+    bool mdev;
     bool reset_works;
     bool needs_reset;
     bool no_mmap;
@@ -231,6 +232,7 @@ void vfio_region_exit(VFIORegion *region);
 void vfio_region_finalize(VFIORegion *region);
 void vfio_reset_handler(void *opaque);
 struct vfio_device_info *vfio_get_device_info(int fd);
+bool vfio_device_is_mdev(VFIODevice *vbasedev);
 bool vfio_attach_device(char *name, VFIODevice *vbasedev,
                         AddressSpace *as, Error **errp);
 void vfio_detach_device(VFIODevice *vbasedev);