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[Xen-devel] [PATCH v2 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>

---
Change in V2:
- trigger CoW is probably not needed on OVMF (as opposed to Mini-OS),
  removed the test.
- comments
- renamed XenbusReadInteger to XenBusReadUint64
- remove callback from IoData, use simple status instead
- return a status from the synchronus io
- Close protocol if blockfront init fail.
- fix few debug print
- Rename XenbusIo to XenBusIo
- XenPvBlkWaitForBackendState will return an error if the new backend
  states is not the expected state.
- Add the license
---
 OvmfPkg/XenPvBlkDxe/BlockFront.c    | 624 ++++++++++++++++++++++++++++++++++++
 OvmfPkg/XenPvBlkDxe/BlockFront.h    |  87 +++++
 OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.c   |  13 +
 OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.inf |   2 +
 4 files changed, 726 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..922c2ec
--- /dev/null
+++ b/OvmfPkg/XenPvBlkDxe/BlockFront.c
@@ -0,0 +1,624 @@
+/** @file
+  Minimal block driver for Mini-OS.
+
+  Copyright (c) 2007-2008 Samuel Thibault.
+  Copyright (C) 2014, Citrix Ltd.
+
+  Redistribution and use in source and binary forms, with or without
+  modification, are permitted provided that the following conditions
+  are met:
+  1. Redistributions of source code must retain the above copyright
+     notice, this list of conditions and the following disclaimer.
+  2. Redistributions in binary form must reproduce the above copyright
+     notice, this list of conditions and the following disclaimer in the
+     documentation and/or other materials provided with the distribution.
+
+  THIS SOFTWARE IS PROVIDED BY AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+  ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+  ARE DISCLAIMED.  IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
+  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+  OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+  HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+  LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+  OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+  SUCH DAMAGE.
+**/
+
+#include <Library/PrintLib.h>
+#include <Library/DebugLib.h>
+
+#include "BlockFront.h"
+
+#include <IndustryStandard/Xen/io/protocols.h>
+#include <IndustryStandard/Xen/io/xenbus.h>
+
+//
+// Header used for UINT32_MAX and UINT16_MAX
+//
+#include "inttypes.h"
+
+/**
+  Helper to read an interger from XenStore.
+
+  @param This         A pointer to a XENBUS_PROTOCOL instance.
+  @param Node         The XenStore node to read from.
+  @param FromBackend  Read frontend or backend value.
+  @param ValuePtr     Where to put the value.
+
+  @retval XENSTORE_STATUS_SUCCESS  If succefull, will update ValuePtr.
+  @return                          Any other return value indicate the error,
+                                   ValuePtr is not updated in this case.
+**/
+STATIC
+XENSTORE_STATUS
+XenBusReadUint64 (
+  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;
+  }
+  // FIXME Will ASSERT if p overflow UINT64 ...
+  *ValuePtr = AsciiStrDecimalToUint64 (p);
+  FreePool (p);
+  return Status;
+}
+
+/**
+  Free an instance of XEN_BLOCK_FRONT_DEVICE.
+
+  @param Dev  The instance to free.
+**/
+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);
+}
+
+/**
+  Wait until until the backend have reach the ExpectedState.
+
+  @param Dev            A XEN_BLOCK_FRONT_DEVICE instance.
+  @param ExpectedState  The backend state expected.
+  @param LastStatePtr   An optionnal pointer where to right the final state.
+
+  @return Return XENSTORE_STATUS_SUCCESS if the new backend state is 
ExpectedState
+          or return an error otherwise.
+**/
+STATIC
+XENSTORE_STATUS
+XenPvBlkWaitForBackendState (
+  IN  XEN_BLOCK_FRONT_DEVICE *Dev,
+  IN  XenbusState            ExpectedState,
+  OUT XenbusState            *LastStatePtr OPTIONAL
+  )
+{
+  XENBUS_PROTOCOL *XenBusIo = Dev->XenBusIo;
+  XenbusState State;
+  UINT64 Value;
+  XENSTORE_STATUS Status = XENSTORE_STATUS_SUCCESS;
+
+  while (TRUE) {
+    Status = XenBusReadUint64 (XenBusIo, "state", TRUE, &Value);
+    if (Status != XENSTORE_STATUS_SUCCESS) {
+      return Status;
+    }
+    if (Value > XenbusStateReconfigured) {
+      //
+      // Value is not a State value.
+      //
+      return XENSTORE_STATUS_EIO;
+    }
+    State = Value;
+    if (State == ExpectedState) {
+      break;
+    } else if (State > ExpectedState) {
+      Status = XENSTORE_STATUS_FAIL;
+      break;
+    }
+    DEBUG ((EFI_D_INFO,
+            "XenPvBlk: waiting backend state %d, current: %d\n",
+            ExpectedState, State));
+    XenBusIo->WaitForWatch (XenBusIo, Dev->StateWatchToken);
+  }
+
+  if (LastStatePtr != NULL) {
+    *LastStatePtr = State;
+  }
+
+  return Status;
+}
+
+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 = XenBusReadUint64 (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));
+    goto Error;
+  }
+
+  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) {
+    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 = XenBusReadUint64 (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 = XenBusReadUint64 (XenBusIo, "sectors", TRUE, 
&Dev->MediaInfo.Sectors);
+  if (Status != XENSTORE_STATUS_SUCCESS) {
+    goto Error2;
+  }
+
+  Status = XenBusReadUint64 (XenBusIo, "sector-size", TRUE, &Value);
+  if (Status != XENSTORE_STATUS_SUCCESS || Value > UINT32_MAX) {
+    goto Error2;
+  }
+  Dev->MediaInfo.SectorSize = Value;
+
+  // Default value
+  Value = 0;
+  Status = XenBusReadUint64 (XenBusIo, "feature-barrier", TRUE, &Value);
+  if (Value == 1) {
+    Dev->MediaInfo.FeatureBarrier = TRUE;
+  } else {
+    Dev->MediaInfo.FeatureBarrier = FALSE;
+  }
+
+  // Default value
+  Value = 0;
+  XenBusReadUint64 (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 %ld 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");
+  XenBusIo->XsRemove (XenBusIo, XST_NIL, "protocol");
+  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 = XenBusReadUint64 (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");
+  XenBusIo->XsRemove (XenBusIo, XST_NIL, "protocol");
+
+  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, could wait for an event on Dev->EventChannel. */
+    }
+  }
+}
+
+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;
+
+  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;
+    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);
+  }
+}
+
+EFI_STATUS
+XenPvBlockIo (
+  IN OUT XEN_BLOCK_FRONT_IO *IoData,
+  IN     BOOLEAN            IsWrite
+  )
+{
+  //
+  // Status value that correspond to an IO in progress.
+  //
+  IoData->Status = EFI_ALREADY_STARTED;
+  XenPvBlockAsyncIo (IoData, IsWrite);
+
+  while (IoData->Status == EFI_ALREADY_STARTED) {
+    XenPvBlockAsyncIoPoll (IoData->Dev);
+  }
+
+  return IoData->Status;
+}
+
+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 = NULL;
+      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 %p, num bytes %p\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;
+      if (IoData != NULL) {
+        IoData->Status = 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..fb60dbd
--- /dev/null
+++ b/OvmfPkg/XenPvBlkDxe/BlockFront.h
@@ -0,0 +1,87 @@
+#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;
+
+  EFI_STATUS              Status;
+};
+
+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
+  );
+
+EFI_STATUS
+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 00a8a2c..930333f 100644
--- a/OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.c
+++ b/OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.c
@@ -36,6 +36,8 @@
 
 #include "XenPvBlkDxe.h"
 
+#include "BlockFront.h"
+
 
 ///
 /// Driver Binding Protocol instance
@@ -278,6 +280,7 @@ XenPvBlkDxeDriverBindingStart (
 {
   EFI_STATUS Status;
   XENBUS_PROTOCOL *XenBusIo;
+  XEN_BLOCK_FRONT_DEVICE *Dev;
 
   Status = gBS->OpenProtocol (
                 ControllerHandle,
@@ -291,7 +294,17 @@ XenPvBlkDxeDriverBindingStart (
     return Status;
   }
 
+  Status = XenPvBlockFrontInitialization (XenBusIo, XenBusIo->Node, &Dev);
+  if (EFI_ERROR (Status)) {
+    goto CloseProtocol;
+  }
+
   return EFI_SUCCESS;
+
+CloseProtocol:
+  gBS->CloseProtocol (ControllerHandle, &gXenBusProtocolGuid,
+                      This->DriverBindingHandle, ControllerHandle);
+  return Status;
 }
 
 /**
diff --git a/OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.inf 
b/OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.inf
index aaa809f..619ed8f 100644
--- a/OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.inf
+++ b/OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.inf
@@ -50,6 +50,8 @@
   XenPvBlkDxe.c
   ComponentName.c
   ComponentName.h
+  BlockFront.c
+  BlockFront.h
 
 
 [LibraryClasses]
-- 
Anthony PERARD


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