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. The protocol used is
describe in the blkif.h header.

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

Change in V4:
- add file header to BlockFront.h (license, copyright, brief desc)

Change in V3:
- Improve comment of XenBusReadUint64.
- Moving blkif.h to this patch
  with the necessary #pragma pack(4) applied for Ia32.
- Add a note about the license in the commit message
- Add "The protocol used is describe in the blkif.h header." in the
  commit message
- Have a mandatory sector-size multiple of 512 or fail to initialize.
- use Sector instead of Offset for IO request.
  with Sector been 512-byte unit.
- print something if EventChannelNotify return an error.

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

License: This patch adds some files which are under the MIT license.
Signed-off-by: Samuel Thibault <samuel.thibault@eu.citrix.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Jordan Justen <jordan.l.justen@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16273 6f19259b-4bc3-4df7-8a09-765794883524

OvmfPkg/XenPvBlkDxe/BlockFront.c

@@ -0,0 +1,647 @@
+/** @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 integer from XenStore.
+
+  If the number overflows according to the range defined by UINT64,
+  then ASSERT().
+
+  @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 *Ptr;
+
+  if (!FromBackend) {
+    Status = This->XsRead (This, XST_NIL, Node, (VOID**)&Ptr);
+  } else {
+    Status = This->XsBackendRead (This, XST_NIL, Node, (VOID**)&Ptr);
+  }
+  if (Status != XENSTORE_STATUS_SUCCESS) {
+    return Status;
+  }
+  // AsciiStrDecimalToUint64 will ASSERT if Ptr overflow UINT64.
+  *ValuePtr = AsciiStrDecimalToUint64 (Ptr);
+  FreePool (Ptr);
+  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 has reached the ExpectedState.
+
+  @param Dev            A XEN_BLOCK_FRONT_DEVICE instance.
+  @param ExpectedState  The backend state expected.
+  @param LastStatePtr   An optional 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 to 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 for 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;
+  }
+  if (Value % 512 != 0) {
+    //
+    // This is not supported by the driver.
+    //
+    DEBUG ((EFI_D_ERROR, "XenPvBlk: Unsupported sector-size value %d, "
+            "it must be a multiple of 512\n", Value));
+    goto Error2;
+  }
+  Dev->MediaInfo.SectorSize = Value;
+
+  // Default value
+  Value = 0;
+  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->Sector & ((Dev->MediaInfo.SectorSize / 512) - 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->Sector;
+
+  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) {
+    UINT32 ReturnCode;
+    ReturnCode = XenBusIo->EventChannelNotify (XenBusIo, Dev->EventChannel);
+    if (ReturnCode != 0) {
+      DEBUG ((EFI_D_ERROR,
+              "XenPvBlk: Unexpected return value from EventChannelNotify: %d\n",
+              ReturnCode));
+    }
+  }
+}
+
+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;
+    UINT32 ReturnCode;
+    ReturnCode = XenBusIo->EventChannelNotify (XenBusIo, Dev->EventChannel);
+    if (ReturnCode != 0) {
+      DEBUG ((EFI_D_ERROR,
+              "XenPvBlk: Unexpected return value from EventChannelNotify: %d\n",
+              ReturnCode));
+    }
+  }
+}
+
+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 sector %p, num bytes %p\n",
+                    Response->operation == BLKIF_OP_READ ? "read" : "write",
+                    Status, IoData->Dev->NodeName,
+                    IoData->Sector,
+                    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);
+}