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[Xen-devel] [PATCH RFC 17/18] OvmfPkg/XenPvBlkDxe: Add BlockFront client.



This is the code that will do the actual communication between OVMF and
a PV block backend, where the block device lives.

This implementation originally comes from Mini-OS, a part of the Xen
Project.

Signed-off-by: Samuel Thibault <samuel.thibault@xxxxxxxxxxxxx>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
---
 OvmfPkg/XenPvBlkDxe/BlockFront.c    | 583 ++++++++++++++++++++++++++++++++++++
 OvmfPkg/XenPvBlkDxe/BlockFront.h    |  88 ++++++
 OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.c   |   8 +
 OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.inf |   2 +
 4 files changed, 681 insertions(+)
 create mode 100644 OvmfPkg/XenPvBlkDxe/BlockFront.c
 create mode 100644 OvmfPkg/XenPvBlkDxe/BlockFront.h

diff --git a/OvmfPkg/XenPvBlkDxe/BlockFront.c b/OvmfPkg/XenPvBlkDxe/BlockFront.c
new file mode 100644
index 0000000..ff5641c
--- /dev/null
+++ b/OvmfPkg/XenPvBlkDxe/BlockFront.c
@@ -0,0 +1,583 @@
+/* Minimal block driver for Mini-OS.
+ * Copyright (c) 2007-2008 Samuel Thibault.
+ * Based on netfront.c.
+ */
+
+#include <Library/PrintLib.h>
+#include <Library/DebugLib.h>
+
+#include "BlockFront.h"
+
+#include <IndustryStandard/Xen/io/protocols.h>
+#include <IndustryStandard/Xen/io/xenbus.h>
+
+#include "inttypes.h"
+
+STATIC
+XENSTORE_STATUS
+XenbusReadInteger (
+  IN  XENBUS_PROTOCOL *This,
+  IN  CONST CHAR8 *Node,
+  IN  BOOLEAN FromBackend,
+  OUT UINT64 *ValuePtr
+  )
+{
+  XENSTORE_STATUS Status;
+  CHAR8 *p;
+
+  if (!FromBackend) {
+    Status = This->XsRead (This, XST_NIL, Node, (VOID**)&p);
+  } else {
+    Status = This->XsBackendRead (This, XST_NIL, Node, (VOID**)&p);
+  }
+  if (Status != XENSTORE_STATUS_SUCCESS) {
+    return Status;
+  }
+  // XXX Will assert if p overflow UINT64 ...
+  *ValuePtr = AsciiStrDecimalToUint64 (p);
+  FreePool (p);
+  return Status;
+}
+
+STATIC
+VOID
+XenPvBlockFree (
+  IN XEN_BLOCK_FRONT_DEVICE *Dev
+  )
+{
+  XENBUS_PROTOCOL *XenbusIo = Dev->XenbusIo;
+
+  if (Dev->RingRef != 0) {
+    XenbusIo->GrantEndAccess (XenbusIo, Dev->RingRef);
+  }
+  if (Dev->Ring.sring != NULL) {
+    FreePages (Dev->Ring.sring, 1);
+  }
+  if (Dev->EventChannel != 0) {
+    XenbusIo->EventChannelClose (XenbusIo, Dev->EventChannel);
+  }
+  FreePool (Dev);
+}
+
+XENSTORE_STATUS
+XenPvBlkWaitForBackendState (
+  IN  XEN_BLOCK_FRONT_DEVICE *Dev,
+  IN  XenbusState            WaitedState,
+  OUT XenbusState            *LastStatePtr OPTIONAL
+  )
+{
+  XENBUS_PROTOCOL *XenbusIo = Dev->XenbusIo;
+  XenbusState State;
+  UINT64 Value;
+  XENSTORE_STATUS Status;
+
+  while (TRUE) {
+    Status = XenbusReadInteger (XenbusIo, "state", TRUE, &Value);
+    if (Status != XENSTORE_STATUS_SUCCESS) {
+      return Status;
+    }
+    if (Value > XenbusStateReconfigured) {
+      return XENSTORE_STATUS_EIO;
+    }
+    State = Value;
+    if (State >= WaitedState) {
+      break;
+    }
+    DEBUG ((EFI_D_INFO,
+            "XenPvBlk: waiting backend state %d, current: %d\n",
+            WaitedState, State));
+    XenbusIo->WaitForWatch (XenbusIo, Dev->StateWatchToken);
+  }
+
+  if (LastStatePtr != NULL) {
+    *LastStatePtr = State;
+  }
+
+  return XENSTORE_STATUS_SUCCESS;
+}
+
+EFI_STATUS
+XenPvBlockFrontInitialization (
+  IN  XENBUS_PROTOCOL         *XenbusIo,
+  IN  CONST CHAR8             *NodeName,
+  OUT XEN_BLOCK_FRONT_DEVICE  **DevPtr
+  )
+{
+  XENSTORE_TRANSACTION xbt;
+  CHAR8 *DeviceType;
+  blkif_sring_t *SharedRing;
+  XENSTORE_STATUS Status;
+  XEN_BLOCK_FRONT_DEVICE *Dev;
+  XenbusState State;
+  UINT64 Value;
+
+  ASSERT (NodeName != NULL);
+
+  Dev = AllocateZeroPool (sizeof (XEN_BLOCK_FRONT_DEVICE));
+  Dev->Signature = XEN_BLOCK_FRONT_SIGNATURE;
+  Dev->NodeName = NodeName;
+  Dev->XenbusIo = XenbusIo;
+  Dev->DeviceId = XenbusIo->DeviceId;
+
+  XenbusIo->XsRead (XenbusIo, XST_NIL, "device-type", (VOID**)&DeviceType);
+  if (AsciiStrCmp (DeviceType, "cdrom") == 0) {
+    Dev->MediaInfo.CdRom = TRUE;
+  } else {
+    Dev->MediaInfo.CdRom = FALSE;
+  }
+  FreePool (DeviceType);
+
+  Status = XenbusReadInteger (XenbusIo, "backend-id", FALSE, &Value);
+  if (Status != XENSTORE_STATUS_SUCCESS || Value > UINT16_MAX) {
+    DEBUG ((EFI_D_ERROR, "XenPvBlk: Failed to get backend-id (%d)\n",
+            Status));
+    goto Error;
+  }
+  Dev->DomainId = Value;
+  XenbusIo->EventChannelAllocate (XenbusIo, Dev->DomainId, &Dev->EventChannel);
+
+  SharedRing = (blkif_sring_t*) AllocatePages (1);
+  SHARED_RING_INIT (SharedRing);
+  FRONT_RING_INIT (&Dev->Ring, SharedRing, EFI_PAGE_SIZE);
+  XenbusIo->GrantAccess (XenbusIo,
+                         Dev->DomainId,
+                         (INTN) SharedRing >> EFI_PAGE_SHIFT,
+                         FALSE,
+                         &Dev->RingRef);
+
+Again:
+  Status = XenbusIo->XsTransactionStart (XenbusIo, &xbt);
+  if (Status != XENSTORE_STATUS_SUCCESS) {
+    DEBUG ((EFI_D_WARN, "XenPvBlk: Failed to start transaction, %d\n", 
Status));
+  }
+
+  Status = XenbusIo->XsPrintf (XenbusIo, xbt, NodeName, "ring-ref", "%d",
+                               Dev->RingRef);
+  if (Status != XENSTORE_STATUS_SUCCESS) {
+    DEBUG ((EFI_D_ERROR, "XenPvBlk: Failed to write ring-ref.\n"));
+    goto AbortTransaction;
+  }
+  Status = XenbusIo->XsPrintf (XenbusIo, xbt, NodeName,
+                               "event-channel", "%d", Dev->EventChannel);
+  if (Status != XENSTORE_STATUS_SUCCESS) {
+    DEBUG ((EFI_D_ERROR, "XenPvBlk: Failed to write event-channel.\n"));
+    goto AbortTransaction;
+  }
+  Status = XenbusIo->XsPrintf (XenbusIo, xbt, NodeName,
+                               "protocol", "%a", XEN_IO_PROTO_ABI_NATIVE);
+  if (Status != XENSTORE_STATUS_SUCCESS) {
+    DEBUG ((EFI_D_ERROR, "XenPvBlk: Failed to write protocol.\n"));
+    goto AbortTransaction;
+  }
+
+  Status = XenbusIo->SetState (XenbusIo, xbt, XenbusStateConnected);
+  if (Status != XENSTORE_STATUS_SUCCESS) {
+    DEBUG ((EFI_D_ERROR, "XenPvBlk: Failed switch state.\n"));
+    goto AbortTransaction;
+  }
+
+  Status = XenbusIo->XsTransactionEnd (XenbusIo, xbt, FALSE);
+  if (Status == XENSTORE_STATUS_EAGAIN) {
+    goto Again;
+  }
+
+  XenbusIo->RegisterWatchBackend (XenbusIo, "state", &Dev->StateWatchToken);
+
+  // Waiting backend
+  Status = XenPvBlkWaitForBackendState (Dev, XenbusStateConnected, &State);
+  if (Status != XENSTORE_STATUS_SUCCESS || State != XenbusStateConnected) {
+    DEBUG ((EFI_D_ERROR,
+            "XenPvBlk: backend for %a/%d not available, rc=%d state=%d\n",
+            XenbusIo->Type, XenbusIo->DeviceId, Status, State));
+    goto Error2;
+  }
+
+  Status = XenbusReadInteger (XenbusIo, "info", TRUE, &Value);
+  if (Status != XENSTORE_STATUS_SUCCESS || Value > UINT32_MAX) {
+    goto Error2;
+  }
+  Dev->MediaInfo.VDiskInfo = Value;
+  if (Dev->MediaInfo.VDiskInfo & VDISK_READONLY) {
+    Dev->MediaInfo.ReadWrite = FALSE;
+  } else {
+    Dev->MediaInfo.ReadWrite = TRUE;
+  }
+
+  Status = XenbusReadInteger (XenbusIo, "sectors", TRUE, 
&Dev->MediaInfo.Sectors);
+  if (Status != XENSTORE_STATUS_SUCCESS) {
+    goto Error2;
+  }
+
+  Status = XenbusReadInteger (XenbusIo, "sector-size", TRUE, &Value);
+  if (Status != XENSTORE_STATUS_SUCCESS || Value > UINT32_MAX) {
+    goto Error2;
+  }
+  Dev->MediaInfo.SectorSize = Value;
+
+  // Default value
+  Value = 0;
+  Status = XenbusReadInteger (XenbusIo, "feature-barrier", TRUE, &Value);
+  if (Value == 1) {
+    Dev->MediaInfo.FeatureBarrier = TRUE;
+  } else {
+    Dev->MediaInfo.FeatureBarrier = FALSE;
+  }
+
+  // Default value
+  Value = 0;
+  XenbusReadInteger (XenbusIo, "feature-flush-cache", TRUE, &Value);
+  if (Value == 1) {
+    Dev->MediaInfo.FeatureFlushCache = TRUE;
+  } else {
+    Dev->MediaInfo.FeatureFlushCache = FALSE;
+  }
+
+  DEBUG ((EFI_D_INFO, "XenPvBlk: New disk with %d sectors of %d bytes\n",
+          Dev->MediaInfo.Sectors, Dev->MediaInfo.SectorSize));
+
+  *DevPtr = Dev;
+  return EFI_SUCCESS;
+
+Error2:
+  XenbusIo->UnregisterWatch (XenbusIo, Dev->StateWatchToken);
+  XenbusIo->XsRemove (XenbusIo, XST_NIL, "ring-ref");
+  XenbusIo->XsRemove (XenbusIo, XST_NIL, "event-channel");
+  goto Error;
+AbortTransaction:
+  XenbusIo->XsTransactionEnd (XenbusIo, xbt, TRUE);
+Error:
+  XenPvBlockFree (Dev);
+  return EFI_DEVICE_ERROR;
+}
+
+VOID
+XenPvBlockFrontShutdown (
+  IN XEN_BLOCK_FRONT_DEVICE *Dev
+  )
+{
+  XENBUS_PROTOCOL *XenbusIo = Dev->XenbusIo;
+  XENSTORE_STATUS Status;
+  UINT64 Value;
+
+  XenPvBlockSync (Dev);
+
+  Status = XenbusIo->SetState (XenbusIo, XST_NIL, XenbusStateClosing);
+  if (Status != XENSTORE_STATUS_SUCCESS) {
+    DEBUG ((EFI_D_ERROR,
+            "XenPvBlk: error while changing state to Closing: %d\n",
+            Status));
+    goto Close;
+  }
+
+  Status = XenPvBlkWaitForBackendState (Dev, XenbusStateClosing, NULL);
+  if (Status != XENSTORE_STATUS_SUCCESS) {
+    DEBUG ((EFI_D_ERROR,
+            "XenPvBlk: error while waiting for closing backend state: %d\n",
+            Status));
+    goto Close;
+  }
+
+  Status = XenbusIo->SetState (XenbusIo, XST_NIL, XenbusStateClosed);
+  if (Status != XENSTORE_STATUS_SUCCESS) {
+    DEBUG ((EFI_D_ERROR,
+            "XenPvBlk: error while changing state to Closed: %d\n",
+            Status));
+    goto Close;
+  }
+
+  Status = XenPvBlkWaitForBackendState (Dev, XenbusStateClosed, NULL);
+  if (Status != XENSTORE_STATUS_SUCCESS) {
+    DEBUG ((EFI_D_ERROR,
+            "XenPvBlk: error while waiting for closed backend state: %d\n",
+            Status));
+    goto Close;
+  }
+
+  Status = XenbusIo->SetState (XenbusIo, XST_NIL, XenbusStateInitialising);
+  if (Status != XENSTORE_STATUS_SUCCESS) {
+    DEBUG ((EFI_D_ERROR,
+            "XenPvBlk: error while changing state to initialising: %d\n",
+            Status));
+    goto Close;
+  }
+
+  while (TRUE) {
+    Status = XenbusReadInteger (XenbusIo, "state", TRUE, &Value);
+    if (Status != XENSTORE_STATUS_SUCCESS) {
+      DEBUG ((EFI_D_ERROR,
+              "XenPvBlk: error while waiting for new backend state: %d\n",
+              Status));
+      goto Close;
+    }
+    if (Value < XenbusStateInitWait || Value >= XenbusStateClosed) {
+      break;
+    }
+    DEBUG ((EFI_D_INFO,
+            "XenPvBlk: waiting backend state %d, current: %d\n",
+            XenbusStateInitWait, Value));
+    XenbusIo->WaitForWatch (XenbusIo, Dev->StateWatchToken);
+  }
+
+Close:
+  XenbusIo->UnregisterWatch (XenbusIo, Dev->StateWatchToken);
+  XenbusIo->XsRemove (XenbusIo, XST_NIL, "ring-ref");
+  XenbusIo->XsRemove (XenbusIo, XST_NIL, "event-channel");
+
+  XenPvBlockFree (Dev);
+}
+
+STATIC
+VOID
+XenPvBlockWaitSlot (
+  IN XEN_BLOCK_FRONT_DEVICE *Dev
+  )
+{
+  /* Wait for a slot */
+  if (RING_FULL (&Dev->Ring)) {
+    while (TRUE) {
+      XenPvBlockAsyncIoPoll (Dev);
+      if (!RING_FULL(&Dev->Ring)) {
+        break;
+      }
+      /* Really no slot, go to sleep. */
+      // XXX wait for an event on Dev->EventChannel
+      DEBUG ((EFI_D_INFO, "%a %d, waiting\n", __func__, __LINE__));
+    }
+  }
+}
+
+/* Issue an aio */
+VOID
+XenPvBlockAsyncIo (
+  IN OUT XEN_BLOCK_FRONT_IO *IoData,
+  IN     BOOLEAN            IsWrite
+  )
+{
+  XEN_BLOCK_FRONT_DEVICE *Dev = IoData->Dev;
+  XENBUS_PROTOCOL *XenbusIo = Dev->XenbusIo;
+  blkif_request_t *Request;
+  RING_IDX RingIndex;
+  BOOLEAN Notify;
+  INT32 NumSegments, Index;
+  UINTN Start, End;
+
+  // Can't io at non-sector-aligned location
+  ASSERT(!(IoData->Offset & (Dev->MediaInfo.SectorSize - 1)));
+  // Can't io non-sector-sized amounts
+  ASSERT(!(IoData->Size & (Dev->MediaInfo.SectorSize - 1)));
+  // Can't io non-sector-aligned buffer
+  ASSERT(!((UINTN) IoData->Buffer & (Dev->MediaInfo.SectorSize - 1)));
+
+  Start = (UINTN) IoData->Buffer & ~EFI_PAGE_MASK;
+  End = ((UINTN) IoData->Buffer + IoData->Size + EFI_PAGE_SIZE - 1) & 
~EFI_PAGE_MASK;
+  IoData->NumRef = NumSegments = (End - Start) / EFI_PAGE_SIZE;
+
+  // XXX is this comment still true ?
+  /* qemu's IDE max multsect is 16 (8KB) and SCSI max DMA was set to 32KB,
+   * so max 44KB can't happen */
+  ASSERT (NumSegments <= BLKIF_MAX_SEGMENTS_PER_REQUEST);
+
+  XenPvBlockWaitSlot (Dev);
+  RingIndex = Dev->Ring.req_prod_pvt;
+  Request = RING_GET_REQUEST (&Dev->Ring, RingIndex);
+
+  Request->operation = IsWrite ? BLKIF_OP_WRITE : BLKIF_OP_READ;
+  Request->nr_segments = NumSegments;
+  Request->handle = Dev->DeviceId;
+  Request->id = (UINTN) IoData;
+  Request->sector_number = IoData->Offset / 512;
+
+  for (Index = 0; Index < NumSegments; Index++) {
+    Request->seg[Index].first_sect = 0;
+    Request->seg[Index].last_sect = EFI_PAGE_SIZE / 512 - 1;
+  }
+  Request->seg[0].first_sect = ((UINTN) IoData->Buffer & EFI_PAGE_MASK) / 512;
+  Request->seg[NumSegments - 1].last_sect =
+      (((UINTN) IoData->Buffer + IoData->Size - 1) & EFI_PAGE_MASK) / 512;
+  for (Index = 0; Index < NumSegments; Index++) {
+    UINTN Data = Start + Index * EFI_PAGE_SIZE;
+    if (!IsWrite) {
+      /* Trigger CoW if needed */
+      *(CHAR8 *)(Data + (Request->seg[Index].first_sect << 9)) = 0;
+      MemoryFence ();
+    }
+    XenbusIo->GrantAccess (XenbusIo, Dev->DomainId,
+                           Data >> EFI_PAGE_SHIFT, IsWrite,
+                           &Request->seg[Index].gref);
+    IoData->GrantRef[Index] = Request->seg[Index].gref;
+  }
+
+  Dev->Ring.req_prod_pvt = RingIndex + 1;
+
+  MemoryFence ();
+  RING_PUSH_REQUESTS_AND_CHECK_NOTIFY (&Dev->Ring, Notify);
+
+  if (Notify) {
+    XenbusIo->EventChannelNotify (XenbusIo, Dev->EventChannel);
+  }
+}
+
+STATIC
+VOID
+XenPvBlockAsyncIoCallback (
+  IN OUT XEN_BLOCK_FRONT_IO *IoData,
+  IN     EFI_STATUS         Status
+  )
+{
+  IoData->Data = (VOID *) 1;
+  IoData->Callback = NULL;
+}
+
+VOID
+XenPvBlockIo (
+  IN OUT XEN_BLOCK_FRONT_IO *IoData,
+  IN     BOOLEAN            IsWrite
+  )
+{
+  ASSERT (IoData->Callback == NULL);
+  // XXX Signal/Event instead ?
+  IoData->Callback = XenPvBlockAsyncIoCallback;
+  XenPvBlockAsyncIo (IoData, IsWrite);
+  IoData->Data = NULL;
+
+  while (TRUE) {
+    XenPvBlockAsyncIoPoll (IoData->Dev);
+    if (IoData->Data) {
+      break;
+    }
+  }
+}
+
+STATIC
+VOID
+XenPvBlockPushOperation (
+  IN XEN_BLOCK_FRONT_DEVICE *Dev,
+  IN UINT8                  Operation,
+  IN UINT64                 Id
+  )
+{
+  INT32 Index;
+  blkif_request_t *Request;
+  BOOLEAN Notify;
+
+  XenPvBlockWaitSlot (Dev);
+  Index = Dev->Ring.req_prod_pvt;
+  Request = RING_GET_REQUEST(&Dev->Ring, Index);
+  Request->operation = Operation;
+  Request->nr_segments = 0;
+  Request->handle = Dev->DeviceId;
+  Request->id = Id;
+  /* Not needed anyway, but the backend will check it */
+  Request->sector_number = 0;
+  Dev->Ring.req_prod_pvt = Index + 1;
+  MemoryFence ();
+  RING_PUSH_REQUESTS_AND_CHECK_NOTIFY (&Dev->Ring, Notify);
+  if (Notify) {
+    XENBUS_PROTOCOL *XenbusIo = Dev->XenbusIo;
+    XenbusIo->EventChannelNotify (XenbusIo, Dev->EventChannel);
+  }
+}
+
+VOID
+XenPvBlockSync (
+  IN XEN_BLOCK_FRONT_DEVICE *Dev
+  )
+{
+  if (Dev->MediaInfo.ReadWrite) {
+    if (Dev->MediaInfo.FeatureBarrier) {
+      XenPvBlockPushOperation (Dev, BLKIF_OP_WRITE_BARRIER, 0);
+    }
+
+    if (Dev->MediaInfo.FeatureFlushCache) {
+      XenPvBlockPushOperation (Dev, BLKIF_OP_FLUSH_DISKCACHE, 0);
+    }
+  }
+
+  /* Note: This won't finish if another thread enqueues requests.  */
+  while (TRUE) {
+    XenPvBlockAsyncIoPoll (Dev);
+    if (RING_FREE_REQUESTS (&Dev->Ring) == RING_SIZE (&Dev->Ring)) {
+      break;
+    }
+  }
+}
+
+VOID
+XenPvBlockAsyncIoPoll (
+  IN XEN_BLOCK_FRONT_DEVICE *Dev
+  )
+{
+  RING_IDX ProducerIndex, ConsumerIndex;
+  blkif_response_t *Response;
+  INT32 More;
+
+  do {
+    ProducerIndex = Dev->Ring.sring->rsp_prod;
+    /* Ensure we see queued responses up to 'ProducerIndex'. */
+    MemoryFence ();
+    ConsumerIndex = Dev->Ring.rsp_cons;
+
+    while (ConsumerIndex != ProducerIndex) {
+      XEN_BLOCK_FRONT_IO *IoData;
+      INT16 Status;
+
+      Response = RING_GET_RESPONSE (&Dev->Ring, ConsumerIndex);
+
+      IoData = (VOID *) (UINTN) Response->id;
+      Status = Response->status;
+
+      switch (Response->operation) {
+      case BLKIF_OP_READ:
+      case BLKIF_OP_WRITE:
+        {
+          INT32 Index;
+
+          if (Status != BLKIF_RSP_OKAY) {
+            DEBUG ((EFI_D_ERROR,
+                    "XenPvBlk: "
+                    "%a error %d on %a at offset %Ld, num bytes %Ld\n",
+                    Response->operation == BLKIF_OP_READ ? "read" : "write",
+                    Status, IoData->Dev->NodeName,
+                    IoData->Offset,
+                    IoData->Size));
+          }
+
+          for (Index = 0; Index < IoData->NumRef; Index++) {
+            Dev->XenbusIo->GrantEndAccess (Dev->XenbusIo, 
IoData->GrantRef[Index]);
+          }
+
+          break;
+        }
+
+      case BLKIF_OP_WRITE_BARRIER:
+        if (Status != BLKIF_RSP_OKAY) {
+          DEBUG ((EFI_D_ERROR, "XenPvBlk: write barrier error %d\n", Status));
+        }
+        break;
+      case BLKIF_OP_FLUSH_DISKCACHE:
+        if (Status != BLKIF_RSP_OKAY) {
+          DEBUG ((EFI_D_ERROR, "XenPvBlk: flush error %d\n", Status));
+        }
+        break;
+
+      default:
+        DEBUG ((EFI_D_ERROR,
+                "XenPvBlk: unrecognized block operation %d response (status 
%d)\n",
+                Response->operation, Status));
+        break;
+      }
+
+      Dev->Ring.rsp_cons = ++ConsumerIndex;
+      /* Nota: callback frees IoData itself */
+      if (IoData && IoData->Callback) {
+        IoData->Callback (IoData, Status ? EFI_DEVICE_ERROR : EFI_SUCCESS);
+      }
+      if (Dev->Ring.rsp_cons != ConsumerIndex) {
+        /* We reentered, we must not continue here */
+        break;
+      }
+    }
+
+    RING_FINAL_CHECK_FOR_RESPONSES (&Dev->Ring, More);
+  } while (More != 0);
+}
diff --git a/OvmfPkg/XenPvBlkDxe/BlockFront.h b/OvmfPkg/XenPvBlkDxe/BlockFront.h
new file mode 100644
index 0000000..d319e0d
--- /dev/null
+++ b/OvmfPkg/XenPvBlkDxe/BlockFront.h
@@ -0,0 +1,88 @@
+#include "XenPvBlkDxe.h"
+
+#include <IndustryStandard/Xen/event_channel.h>
+#include <IndustryStandard/Xen/io/blkif.h>
+
+typedef struct _XEN_BLOCK_FRONT_DEVICE XEN_BLOCK_FRONT_DEVICE;
+typedef struct _XEN_BLOCK_FRONT_IO XEN_BLOCK_FRONT_IO;
+
+struct _XEN_BLOCK_FRONT_IO
+{
+  XEN_BLOCK_FRONT_DEVICE  *Dev;
+  UINT8                   *Buffer;
+  UINTN                   Size;
+  UINTN                   Offset;
+
+  grant_ref_t             GrantRef[BLKIF_MAX_SEGMENTS_PER_REQUEST];
+  INT32                   NumRef;
+
+  VOID (*Callback)(XEN_BLOCK_FRONT_IO *aiocb, EFI_STATUS Status);
+  VOID  *Data;
+};
+
+typedef struct
+{
+  UINT64    Sectors;
+  UINT32    SectorSize;
+  UINT32    VDiskInfo;
+  BOOLEAN   ReadWrite;
+  BOOLEAN   CdRom;
+  BOOLEAN   FeatureBarrier;
+  BOOLEAN   FeatureFlushCache;
+} XEN_BLOCK_FRONT_MEDIA_INFO;
+
+#define XEN_BLOCK_FRONT_SIGNATURE SIGNATURE_32 ('X', 'p', 'v', 'B')
+struct _XEN_BLOCK_FRONT_DEVICE {
+  UINT32                      Signature;
+  EFI_BLOCK_IO_PROTOCOL       BlockIo;
+  domid_t                     DomainId;
+
+  blkif_front_ring_t          Ring;
+  grant_ref_t                 RingRef;
+  evtchn_port_t               EventChannel;
+  blkif_vdev_t                DeviceId;
+
+  CONST CHAR8                 *NodeName;
+  XEN_BLOCK_FRONT_MEDIA_INFO  MediaInfo;
+
+  VOID                        *StateWatchToken;
+
+  XENBUS_PROTOCOL             *XenbusIo;
+};
+
+#define XEN_BLOCK_FRONT_FROM_BLOCK_IO(b) \
+  CR (b, XEN_BLOCK_FRONT_DEVICE, BlockIo, XEN_BLOCK_FRONT_SIGNATURE)
+
+EFI_STATUS
+XenPvBlockFrontInitialization (
+  IN  XENBUS_PROTOCOL  *XenbusIo,
+  IN  CONST CHAR8      *NodeName,
+  OUT XEN_BLOCK_FRONT_DEVICE **DevPtr
+  );
+
+VOID
+XenPvBlockFrontShutdown (
+  IN XEN_BLOCK_FRONT_DEVICE *Dev
+  );
+
+VOID
+XenPvBlockAsyncIo (
+  IN OUT XEN_BLOCK_FRONT_IO *IoData,
+  IN     BOOLEAN            IsWrite
+  );
+
+VOID
+XenPvBlockIo (
+  IN OUT XEN_BLOCK_FRONT_IO *IoData,
+  IN     BOOLEAN            IsWrite
+  );
+
+VOID
+XenPvBlockAsyncIoPoll (
+  IN XEN_BLOCK_FRONT_DEVICE *Dev
+  );
+
+VOID
+XenPvBlockSync (
+  IN XEN_BLOCK_FRONT_DEVICE *Dev
+  );
diff --git a/OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.c 
b/OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.c
index 0ce1e86..7ec7d60 100644
--- a/OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.c
+++ b/OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.c
@@ -12,6 +12,8 @@
 
 #include "XenPvBlkDxe.h"
 
+#include "BlockFront.h"
+
 
 ///
 /// Driver Binding Protocol instance
@@ -263,6 +265,7 @@ XenPvBlkDxeDriverBindingStart (
 {
   EFI_STATUS Status;
   XENBUS_PROTOCOL *XenbusIo;
+  XEN_BLOCK_FRONT_DEVICE *Dev;
 
   Status = gBS->OpenProtocol (
                 ControllerHandle,
@@ -276,6 +279,11 @@ XenPvBlkDxeDriverBindingStart (
     return Status;
   }
 
+  Status = XenPvBlockFrontInitialization (XenbusIo, XenbusIo->Node, &Dev);
+  if (EFI_ERROR (Status)) {
+    return Status;
+  }
+
   return EFI_SUCCESS;
 }
 
diff --git a/OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.inf 
b/OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.inf
index 4444cda..a43d006 100644
--- a/OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.inf
+++ b/OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.inf
@@ -30,6 +30,8 @@
   XenPvBlkDxe.c
   ComponentName.c
   ComponentName.h
+  BlockFront.c
+  BlockFront.h
 
 
 [LibraryClasses]
-- 
Anthony PERARD


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