Re: [Qemu-devel] [RFC] virtio-mmio: implement modern (v2) personality (virtio-1)

[Sergio Lopez]

Michael S. Tsirkin <address@hidden> writes:

> On Mon, Jul 29, 2019 at 02:57:55PM +0200, Sergio Lopez wrote:
>> Implement the modern (v2) personality, according to the VirtIO 1.0
>> specification.
>> 
>> Support for v2 among guests is not as widespread as it'd be
>> desirable. While the Linux driver has had it for a while, support is
>> missing, at least, from Tianocore EDK II, NetBSD and FreeBSD.
>
> The fact that there was no open source hypervisor implementation has
> probably contributed to this :)
>
>> For this reason, the v2 personality is disabled, keeping the legacy
>> behavior as default.
>
> I agree it's a good default for existing machine types.
>
>> Machine types willing to use v2, can enable it
>> using MachineClass's compat_props.
>
> Hmm. Are compat_props really the recommended mechanism to
> tweak defaults? I was under the impression it's
> only for compatibility with old machine types.
> Eduardo, any opinion on this?

Stefan suggested using something like "-global virtio-mmio.modern=true"
which does the trick for the command line, but I'd also like a way to
set it to true by default on microvm. We can discuss the best way to
achieve that (if using compat_props isn't acceptable) on the next
microvm patch series.

>> 
>> Signed-off-by: Sergio Lopez <address@hidden>
>
> Endian-ness seems to be wrong:
>
> static const MemoryRegionOps virtio_mem_ops = {
>     .read = virtio_mmio_read,
>     .write = virtio_mmio_write,
>     .endianness = DEVICE_NATIVE_ENDIAN,
> };
>
> you will see this if you test a big endian guest.

Interesting, a Linux kernel compiled for aarch64_be works just
fine. Looking further, seems like, on ARM, Linux assumes all memory I/O
operations are little-endian and swaps the data if necessary:

arch/arm64/include/asm/io.h:
/*
 * Relaxed I/O memory access primitives. These follow the Device memory
 * ordering rules but do not guarantee any ordering relative to Normal memory
 * accesses.
 */
#define readb_relaxed(c)        ({ u8  __r = __raw_readb(c); __r; })
#define readw_relaxed(c)        ({ u16 __r = le16_to_cpu((__force 
__le16)__raw_readw(c)); __r; })
#define readl_relaxed(c)        ({ u32 __r = le32_to_cpu((__force 
__le32)__raw_readl(c)); __r; })
#define readq_relaxed(c)        ({ u64 __r = le64_to_cpu((__force 
__le64)__raw_readq(c)); __r; })

#define writeb_relaxed(v,c)     ((void)__raw_writeb((v),(c)))
#define writew_relaxed(v,c)     ((void)__raw_writew((__force 
u16)cpu_to_le16(v),(c)))
#define writel_relaxed(v,c)     ((void)__raw_writel((__force 
u32)cpu_to_le32(v),(c)))
#define writeq_relaxed(v,c)     ((void)__raw_writeq((__force 
u64)cpu_to_le64(v),(c)))

The Apendix X from virtio-0.9.5 specs states that "The endianness of the
registers follows the native endianness of the Guest". Luckily for us,
this isn't the case, as with DEVICE_NATIVE_ENDIAN
memory.c:adjust_endianness doesn't attempt any kind of transformation.

In any, I guess we should follow the spec, and keep DEVICE_NATIVE_ENDIAN
for the legacy mode while using DEVICE_LITTLE_ENDIAN for
virtio-mmio-2/virtio-1.

>> ---
>>  hw/virtio/virtio-mmio.c | 264 ++++++++++++++++++++++++++++++++++++++--
>>  1 file changed, 254 insertions(+), 10 deletions(-)
>> 
>> diff --git a/hw/virtio/virtio-mmio.c b/hw/virtio/virtio-mmio.c
>> index 97b7f35496..1da841336f 100644
>> --- a/hw/virtio/virtio-mmio.c
>> +++ b/hw/virtio/virtio-mmio.c
>> @@ -47,14 +47,24 @@
>>          OBJECT_CHECK(VirtIOMMIOProxy, (obj), TYPE_VIRTIO_MMIO)
>>  
>>  #define VIRT_MAGIC 0x74726976 /* 'virt' */
>> -#define VIRT_VERSION 1
>> +#define VIRT_VERSION_LEGACY 1
>> +#define VIRT_VERSION_MODERN 2
>>  #define VIRT_VENDOR 0x554D4551 /* 'QEMU' */
>>  
>> +typedef struct VirtIOMMIOQueue {
>> +    uint16_t num;
>> +    bool enabled;
>> +    uint32_t desc[2];
>> +    uint32_t avail[2];
>> +    uint32_t used[2];
>> +} VirtIOMMIOQueue;
>> +
>>  typedef struct {
>>      /* Generic */
>>      SysBusDevice parent_obj;
>>      MemoryRegion iomem;
>>      qemu_irq irq;
>> +    bool modern;
>>      /* Guest accessible state needing migration and reset */
>>      uint32_t host_features_sel;
>>      uint32_t guest_features_sel;
>> @@ -62,6 +72,9 @@ typedef struct {
>>      /* virtio-bus */
>>      VirtioBusState bus;
>>      bool format_transport_address;
>> +    /* Fields only used for v2 (modern) devices */
>> +    uint32_t guest_features[2];
>> +    VirtIOMMIOQueue vqs[VIRTIO_QUEUE_MAX];
>>  } VirtIOMMIOProxy;
>>  
>>  static bool virtio_mmio_ioeventfd_enabled(DeviceState *d)
>> @@ -115,7 +128,11 @@ static uint64_t virtio_mmio_read(void *opaque, hwaddr 
>> offset, unsigned size)
>>          case VIRTIO_MMIO_MAGIC_VALUE:
>>              return VIRT_MAGIC;
>>          case VIRTIO_MMIO_VERSION:
>> -            return VIRT_VERSION;
>> +            if (proxy->modern) {
>> +                return VIRT_VERSION_MODERN;
>> +            } else {
>> +                return VIRT_VERSION_LEGACY;
>> +            }
>>          case VIRTIO_MMIO_VENDOR_ID:
>>              return VIRT_VENDOR;
>>          default:
>> @@ -146,14 +163,18 @@ static uint64_t virtio_mmio_read(void *opaque, hwaddr 
>> offset, unsigned size)
>>      case VIRTIO_MMIO_MAGIC_VALUE:
>>          return VIRT_MAGIC;
>>      case VIRTIO_MMIO_VERSION:
>> -        return VIRT_VERSION;
>> +        if (proxy->modern) {
>> +            return VIRT_VERSION_MODERN;
>> +        } else {
>> +            return VIRT_VERSION_LEGACY;
>> +        }
>>      case VIRTIO_MMIO_DEVICE_ID:
>>          return vdev->device_id;
>>      case VIRTIO_MMIO_VENDOR_ID:
>>          return VIRT_VENDOR;
>>      case VIRTIO_MMIO_DEVICE_FEATURES:
>>          if (proxy->host_features_sel) {
>> -            return 0;
>> +            return vdev->host_features >> 32;
>
> I'd do vdev->host_features >> (32 * proxy->host_features_sel);

OK, looks nicer. I'll sanitize the value host_features_sel on
VIRTIO_MMIO_DEVICE_FEATURES too, as I'm already doing with
guest_features_sel.

>>          }
>>          return vdev->host_features;
>>      case VIRTIO_MMIO_QUEUE_NUM_MAX:
>> @@ -162,12 +183,34 @@ static uint64_t virtio_mmio_read(void *opaque, hwaddr 
>> offset, unsigned size)
>>          }
>>          return VIRTQUEUE_MAX_SIZE;
>>      case VIRTIO_MMIO_QUEUE_PFN:
>> +        if (proxy->modern) {
>> +            qemu_log_mask(LOG_GUEST_ERROR,
>> +                          "%s: read from legacy register in modern mode\n",
>> +                          __func__);
>> +            return 0;
>> +        }
>>          return virtio_queue_get_addr(vdev, vdev->queue_sel)
>>              >> proxy->guest_page_shift;
>> +    case VIRTIO_MMIO_QUEUE_READY:
>> +        if (!proxy->modern) {
>> +            qemu_log_mask(LOG_GUEST_ERROR,
>> +                          "%s: read from modern register in legacy mode\n",
>> +                          __func__);
>> +            return 0;
>> +        }
>> +        return proxy->vqs[vdev->queue_sel].enabled;
>>      case VIRTIO_MMIO_INTERRUPT_STATUS:
>>          return atomic_read(&vdev->isr);
>>      case VIRTIO_MMIO_STATUS:
>>          return vdev->status;
>> +    case VIRTIO_MMIO_CONFIG_GENERATION:
>> +        if (!proxy->modern) {
>> +            qemu_log_mask(LOG_GUEST_ERROR,
>> +                          "%s: read from modern register in legacy mode\n",
>> +                          __func__);
>> +            return 0;
>> +        }
>> +        return vdev->generation;
>>      case VIRTIO_MMIO_DEVICE_FEATURES_SEL:
>>      case VIRTIO_MMIO_DRIVER_FEATURES:
>>      case VIRTIO_MMIO_DRIVER_FEATURES_SEL:
>> @@ -177,6 +220,12 @@ static uint64_t virtio_mmio_read(void *opaque, hwaddr 
>> offset, unsigned size)
>>      case VIRTIO_MMIO_QUEUE_ALIGN:
>>      case VIRTIO_MMIO_QUEUE_NOTIFY:
>>      case VIRTIO_MMIO_INTERRUPT_ACK:
>> +    case VIRTIO_MMIO_QUEUE_DESC_LOW:
>> +    case VIRTIO_MMIO_QUEUE_DESC_HIGH:
>> +    case VIRTIO_MMIO_QUEUE_AVAIL_LOW:
>> +    case VIRTIO_MMIO_QUEUE_AVAIL_HIGH:
>> +    case VIRTIO_MMIO_QUEUE_USED_LOW:
>> +    case VIRTIO_MMIO_QUEUE_USED_HIGH:
>>          qemu_log_mask(LOG_GUEST_ERROR,
>>                        "%s: read of write-only register\n",
>>                        __func__);
>> @@ -232,14 +281,26 @@ static void virtio_mmio_write(void *opaque, hwaddr 
>> offset, uint64_t value,
>>          proxy->host_features_sel = value;
>>          break;
>>      case VIRTIO_MMIO_DRIVER_FEATURES:
>> -        if (!proxy->guest_features_sel) {
>> +        if (proxy->modern) {
>> +            proxy->guest_features[proxy->guest_features_sel] = value;
>> +        } else if (!proxy->guest_features_sel) {
>>              virtio_set_features(vdev, value);
>>          }
>>          break;
>>      case VIRTIO_MMIO_DRIVER_FEATURES_SEL:
>> -        proxy->guest_features_sel = value;
>> +        if (value) {
>> +            proxy->guest_features_sel = 1;
>> +        } else {
>> +            proxy->guest_features_sel = 0;
>> +        }
>>          break;
>>      case VIRTIO_MMIO_GUEST_PAGE_SIZE:
>> +        if (proxy->modern) {
>> +            qemu_log_mask(LOG_GUEST_ERROR,
>> +                          "%s: write to legacy register in modern mode\n",
>> +                          __func__);
>> +            return;
>> +        }
>>          proxy->guest_page_shift = ctz32(value);
>>          if (proxy->guest_page_shift > 31) {
>>              proxy->guest_page_shift = 0;
>> @@ -253,15 +314,29 @@ static void virtio_mmio_write(void *opaque, hwaddr 
>> offset, uint64_t value,
>>          break;
>>      case VIRTIO_MMIO_QUEUE_NUM:
>>          trace_virtio_mmio_queue_write(value, VIRTQUEUE_MAX_SIZE);
>> -        virtio_queue_set_num(vdev, vdev->queue_sel, value);
>> -        /* Note: only call this function for legacy devices */
>> -        virtio_queue_update_rings(vdev, vdev->queue_sel);
>> +        if (proxy->modern) {
>> +            proxy->vqs[vdev->queue_sel].num = value;
>> +        } else {
>> +            virtio_queue_set_num(vdev, vdev->queue_sel, value);
>> +            virtio_queue_update_rings(vdev, vdev->queue_sel);
>> +        }
>>          break;
>>      case VIRTIO_MMIO_QUEUE_ALIGN:
>> -        /* Note: this is only valid for legacy devices */
>> +        if (proxy->modern) {
>> +            qemu_log_mask(LOG_GUEST_ERROR,
>> +                          "%s: write to legacy register in modern mode\n",
>> +                          __func__);
>> +            return;
>> +        }
>>          virtio_queue_set_align(vdev, vdev->queue_sel, value);
>>          break;
>>      case VIRTIO_MMIO_QUEUE_PFN:
>> +        if (proxy->modern) {
>> +            qemu_log_mask(LOG_GUEST_ERROR,
>> +                          "%s: write to legacy register in modern mode\n",
>> +                          __func__);
>> +            return;
>> +        }
>>          if (value == 0) {
>>              virtio_reset(vdev);
>>          } else {
>> @@ -269,6 +344,24 @@ static void virtio_mmio_write(void *opaque, hwaddr 
>> offset, uint64_t value,
>>                                    value << proxy->guest_page_shift);
>>          }
>>          break;
>> +    case VIRTIO_MMIO_QUEUE_READY:
>> +        if (!proxy->modern) {
>> +            qemu_log_mask(LOG_GUEST_ERROR,
>> +                          "%s: write to modern register in legacy mode\n",
>> +                          __func__);
>> +            return;
>> +        }
>> +        virtio_queue_set_num(vdev, vdev->queue_sel,
>> +                             proxy->vqs[vdev->queue_sel].num);
>> +        virtio_queue_set_rings(vdev, vdev->queue_sel,
>> +                       ((uint64_t)proxy->vqs[vdev->queue_sel].desc[1]) << 
>> 32 |
>> +                       proxy->vqs[vdev->queue_sel].desc[0],
>> +                       ((uint64_t)proxy->vqs[vdev->queue_sel].avail[1]) << 
>> 32 |
>> +                       proxy->vqs[vdev->queue_sel].avail[0],
>> +                       ((uint64_t)proxy->vqs[vdev->queue_sel].used[1]) << 
>> 32 |
>> +                       proxy->vqs[vdev->queue_sel].used[0]);
>> +        proxy->vqs[vdev->queue_sel].enabled = 1;
>> +        break;
>
> This one seems out of spec.
> In this respect virtio mmio is more advanced that virtio pci:
> it allows setting the ready status to 0.

You're right, I'll fix it.

>>      case VIRTIO_MMIO_QUEUE_NOTIFY:
>>          if (value < VIRTIO_QUEUE_MAX) {
>>              virtio_queue_notify(vdev, value);
>> @@ -283,6 +376,12 @@ static void virtio_mmio_write(void *opaque, hwaddr 
>> offset, uint64_t value,
>>              virtio_mmio_stop_ioeventfd(proxy);
>>          }
>>  
>> +        if (proxy->modern && (value & VIRTIO_CONFIG_S_FEATURES_OK)) {
>> +            virtio_set_features(vdev,
>> +                                ((uint64_t)proxy->guest_features[1]) << 32 |
>> +                                proxy->guest_features[0]);
>> +        }
>> +
>>          virtio_set_status(vdev, value & 0xff);
>>  
>>          if (value & VIRTIO_CONFIG_S_DRIVER_OK) {
>> @@ -293,6 +392,60 @@ static void virtio_mmio_write(void *opaque, hwaddr 
>> offset, uint64_t value,
>>              virtio_reset(vdev);
>>          }
>>          break;
>> +    case VIRTIO_MMIO_QUEUE_DESC_LOW:
>> +        if (!proxy->modern) {
>> +            qemu_log_mask(LOG_GUEST_ERROR,
>> +                          "%s: write to legacy register in modern mode\n",
>> +                          __func__);
>> +            return;
>> +        }
>> +        proxy->vqs[vdev->queue_sel].desc[0] = value;
>> +        break;
>> +    case VIRTIO_MMIO_QUEUE_DESC_HIGH:
>> +        if (!proxy->modern) {
>> +            qemu_log_mask(LOG_GUEST_ERROR,
>> +                          "%s: write to legacy register in modern mode\n",
>> +                          __func__);
>> +            return;
>> +        }
>> +        proxy->vqs[vdev->queue_sel].desc[1] = value;
>> +        break;
>> +    case VIRTIO_MMIO_QUEUE_AVAIL_LOW:
>> +        if (!proxy->modern) {
>> +            qemu_log_mask(LOG_GUEST_ERROR,
>> +                          "%s: write to legacy register in modern mode\n",
>> +                          __func__);
>> +            return;
>> +        }
>> +        proxy->vqs[vdev->queue_sel].avail[0] = value;
>> +        break;
>> +    case VIRTIO_MMIO_QUEUE_AVAIL_HIGH:
>> +        if (!proxy->modern) {
>> +            qemu_log_mask(LOG_GUEST_ERROR,
>> +                          "%s: write to legacy register in modern mode\n",
>> +                          __func__);
>> +            return;
>> +        }
>> +        proxy->vqs[vdev->queue_sel].avail[1] = value;
>> +        break;
>> +    case VIRTIO_MMIO_QUEUE_USED_LOW:
>> +        if (!proxy->modern) {
>> +            qemu_log_mask(LOG_GUEST_ERROR,
>> +                          "%s: write to legacy register in modern mode\n",
>> +                          __func__);
>> +            return;
>> +        }
>> +        proxy->vqs[vdev->queue_sel].used[0] = value;
>> +        break;
>> +    case VIRTIO_MMIO_QUEUE_USED_HIGH:
>> +        if (!proxy->modern) {
>> +            qemu_log_mask(LOG_GUEST_ERROR,
>> +                          "%s: write to legacy register in modern mode\n",
>> +                          __func__);
>> +            return;
>> +        }
>> +        proxy->vqs[vdev->queue_sel].used[1] = value;
>> +        break;
>>      case VIRTIO_MMIO_MAGIC_VALUE:
>>      case VIRTIO_MMIO_VERSION:
>>      case VIRTIO_MMIO_DEVICE_ID:
>> @@ -300,6 +453,7 @@ static void virtio_mmio_write(void *opaque, hwaddr 
>> offset, uint64_t value,
>>      case VIRTIO_MMIO_DEVICE_FEATURES:
>>      case VIRTIO_MMIO_QUEUE_NUM_MAX:
>>      case VIRTIO_MMIO_INTERRUPT_STATUS:
>> +    case VIRTIO_MMIO_CONFIG_GENERATION:
>>          qemu_log_mask(LOG_GUEST_ERROR,
>>                        "%s: write to readonly register\n",
>>                        __func__);
>> @@ -349,15 +503,90 @@ static void virtio_mmio_save_config(DeviceState 
>> *opaque, QEMUFile *f)
>>      qemu_put_be32(f, proxy->guest_page_shift);
>>  }
>>  
>> +static const VMStateDescription vmstate_virtio_mmio_modern_queue_state = {
>> +    .name = "virtio_mmio/modern_queue_state",
>> +    .version_id = 1,
>> +    .minimum_version_id = 1,
>> +    .fields = (VMStateField[]) {
>> +        VMSTATE_UINT16(num, VirtIOMMIOQueue),
>> +        VMSTATE_BOOL(enabled, VirtIOMMIOQueue),
>> +        VMSTATE_UINT32_ARRAY(desc, VirtIOMMIOQueue, 2),
>> +        VMSTATE_UINT32_ARRAY(avail, VirtIOMMIOQueue, 2),
>> +        VMSTATE_UINT32_ARRAY(used, VirtIOMMIOQueue, 2),
>> +        VMSTATE_END_OF_LIST()
>> +    }
>> +};
>> +
>> +static const VMStateDescription vmstate_virtio_mmio_modern_state_sub = {
>> +    .name = "virtio_mmio/modern_state",
>> +    .version_id = 1,
>> +    .minimum_version_id = 1,
>> +    .fields = (VMStateField[]) {
>> +        VMSTATE_UINT32_ARRAY(guest_features, VirtIOMMIOProxy, 2),
>> +        VMSTATE_STRUCT_ARRAY(vqs, VirtIOMMIOProxy, VIRTIO_QUEUE_MAX, 0,
>> +                             vmstate_virtio_mmio_modern_queue_state,
>> +                             VirtIOMMIOQueue),
>> +        VMSTATE_END_OF_LIST()
>> +    }
>> +};
>> +
>> +static const VMStateDescription vmstate_virtio_mmio = {
>> +    .name = "virtio_mmio",
>> +    .version_id = 1,
>> +    .minimum_version_id = 1,
>> +    .minimum_version_id_old = 1,
>> +    .fields = (VMStateField[]) {
>> +        VMSTATE_END_OF_LIST()
>> +    },
>> +    .subsections = (const VMStateDescription*[]) {
>> +        &vmstate_virtio_mmio_modern_state_sub,
>> +        NULL
>> +    }
>> +};
>> +
>> +static void virtio_mmio_save_extra_state(DeviceState *opaque, QEMUFile *f)
>> +{
>> +    VirtIOMMIOProxy *proxy = VIRTIO_MMIO(opaque);
>> +
>> +    vmstate_save_state(f, &vmstate_virtio_mmio, proxy, NULL);
>> +}
>> +
>> +static int virtio_mmio_load_extra_state(DeviceState *opaque, QEMUFile *f)
>> +{
>> +    VirtIOMMIOProxy *proxy = VIRTIO_MMIO(opaque);
>> +
>> +    return vmstate_load_state(f, &vmstate_virtio_mmio, proxy, 1);
>> +}
>> +
>> +static bool virtio_mmio_has_extra_state(DeviceState *opaque)
>> +{
>> +    VirtIOMMIOProxy *proxy = VIRTIO_MMIO(opaque);
>> +
>> +    return proxy->modern;
>> +}
>> +
>>  static void virtio_mmio_reset(DeviceState *d)
>>  {
>>      VirtIOMMIOProxy *proxy = VIRTIO_MMIO(d);
>> +    int i;
>>  
>>      virtio_mmio_stop_ioeventfd(proxy);
>>      virtio_bus_reset(&proxy->bus);
>>      proxy->host_features_sel = 0;
>>      proxy->guest_features_sel = 0;
>>      proxy->guest_page_shift = 0;
>> +
>> +    if (proxy->modern) {
>> +        proxy->guest_features[0] = proxy->guest_features[1] = 0;
>> +
>> +        for (i = 0; i < VIRTIO_QUEUE_MAX; i++) {
>> +            proxy->vqs[i].enabled = 0;
>> +            proxy->vqs[i].num = 0;
>> +            proxy->vqs[i].desc[0] = proxy->vqs[i].desc[1] = 0;
>> +            proxy->vqs[i].avail[0] = proxy->vqs[i].avail[1] = 0;
>> +            proxy->vqs[i].used[0] = proxy->vqs[i].used[1] = 0;
>> +        }
>> +    }
>>  }
>>  
>>  static int virtio_mmio_set_guest_notifier(DeviceState *d, int n, bool 
>> assign,
>> @@ -420,11 +649,22 @@ assign_error:
>>      return r;
>>  }
>>  
>> +static void virtio_mmio_pre_plugged(DeviceState *d, Error **errp)
>> +{
>> +    VirtIOMMIOProxy *proxy = VIRTIO_MMIO(d);
>> +    VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
>> +
>> +    if (proxy->modern) {
>> +        virtio_add_feature(&vdev->host_features, VIRTIO_F_VERSION_1);
>> +    }
>> +}
>> +
>>  /* virtio-mmio device */
>>  
>>  static Property virtio_mmio_properties[] = {
>>      DEFINE_PROP_BOOL("format_transport_address", VirtIOMMIOProxy,
>>                       format_transport_address, true),
>> +    DEFINE_PROP_BOOL("modern", VirtIOMMIOProxy, modern, false),
>>      DEFINE_PROP_END_OF_LIST(),
>>  };
>>  
>> @@ -508,9 +748,13 @@ static void virtio_mmio_bus_class_init(ObjectClass 
>> *klass, void *data)
>>      k->notify = virtio_mmio_update_irq;
>>      k->save_config = virtio_mmio_save_config;
>>      k->load_config = virtio_mmio_load_config;
>> +    k->save_extra_state = virtio_mmio_save_extra_state;
>> +    k->load_extra_state = virtio_mmio_load_extra_state;
>> +    k->has_extra_state = virtio_mmio_has_extra_state;
>>      k->set_guest_notifiers = virtio_mmio_set_guest_notifiers;
>>      k->ioeventfd_enabled = virtio_mmio_ioeventfd_enabled;
>>      k->ioeventfd_assign = virtio_mmio_ioeventfd_assign;
>> +    k->pre_plugged = virtio_mmio_pre_plugged;
>>      k->has_variable_vring_alignment = true;
>>      bus_class->max_dev = 1;
>>      bus_class->get_dev_path = virtio_mmio_bus_get_dev_path;
>> -- 
>> 2.21.0

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