Re: [PATCH RFC 17/18] OvmfPkg/XenPvBlkDxe: Add BlockFront client.

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

> > > +  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) {
> > 
> > Not State != WaitedState ?
> 
> I don't think so, the function is actually waiting for the State to be
> equal to WaitedState. At least, that how I wrote it. There might be a
> better algorithm.

Then State == WaitedState

seems the proper way?

> 
> > > +      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));
> > 
> > .. and do you want to error out?
> 
> The original code (mini-os) is continuing in thes case, so I thought it
> was possible to do the initialisation without transaction. But maybe I'm
> wrong and this should be an error.

No explanation in the commit for that?

> 
> > > +  }
> > > +
> > > +  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;
> > 
> > Why not &Dev->MediaInfo.SectorSize in XenbusReadInteger?
> > 
> > Is it because of types? If so, please add a comment stating that.
> 
> Yes, because of the type, uint64 vs uint32.
> 
> Maybe I could rename the XenbusReadInteger to XenbusReadUint64, and it
> would be more obvious that the function require a specific type.

That would be much better. Thank you
> 
> > > +
> > > +  // 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");
> > 
> > XenbusIo->XsRemove (XenbusIo, XST_NIL, "protocol");
> > 
> > ?
> 
> I don't know, but I can do that.
> 
> > > +  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");
> > 
> > "protocol" 

As in, also do the XenbusIo->XsRemove(...)

> > > +
> > > +  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 ?
> > 
> > I think it is outdated, as Linux would do max DMA up to the segment
> > size that is advertised. Ditto for the SCSI stack.
> 
> OK, thanks.
> 
> > > +  /* 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);
> > 
> > But this check is OK as we can't truly fit more on the ring.
> 
> OK.
> 
> > > +
> > > +  XenPvBlockWaitSlot (Dev);
> > 
> > What happens if there are multiple threads calling this
> > function? Don't we need a mutex to only allow
> > one thread to grab an RingIndex?
> 
> So, OVMF does not have threads but the are "events", called by a timer.
> This code does not support it, yet, so I don't need any form of locking,
> yet.

Ok, why don't you mention that in the commit description.
> 
> > > +  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;
> > 
> > Uh? 
> > > +    Request->seg[Index].last_sect = EFI_PAGE_SIZE / 512 - 1;
> > 
> > Uh? I thought you wanted to use the real sector values?
> > > +  }
> > > +  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;
> > 
> > What about in between 0 and NumSegments? You should also
> > fill out those values with valid entries.
> 
> It's done by the previous for loop. Maybe this part is hard to
> understand without the interface explain.
> include io/blkif.h says:
>   @first_sect: first sector in frame to transfer (inclusive).
>   @last_sect: last sector in frame to transfer (inclusive).
> 
> but does not explain what a frame is, beyond this comment on:
>   grant_ref_t gref; /* reference to I/O buffer frame */
> (all this from the struct blkif_request_segment)
> Or maybe frame == page.

That is what it means. If you have a page, with 4 sectors
of data (so half-page) and they are discontingious you
have to enumerate the sector values. For example:

First sector = lba + 0 -> lba + 1; #2 sector = lba + 5-> lba + 6;
#3 sector = lba + 55 -> lba + 56; #4 sector = lba + 32768 -> lba + 32769

> 
> Anyway, the way the segments are initialized feel weirds now, but I
> don't think it's incorrect, otherwise, I would not be able to boot any
> guest.

Well, you could because you might be reading only one sector per
I/O request. And then the first_sect and last_sect get filled
with proper values.
> 
> > > +  for (Index = 0; Index < NumSegments; Index++) {
> > > +    UINTN Data = Start + Index * EFI_PAGE_SIZE;
> > > +    if (!IsWrite) {
> > > +      /* Trigger CoW if needed */
> > 
> > Not sure I understand that reference?
> 
> Maybe a reference to the original commit will help to understand:
> minios: Fix bug when blkfront reading into zero-mapped buffer by just poking the page.
> No need to use virtual_to_mfn() for the ring since that is a real page.
> 7b1257946080b63421a8dc59c7b3dfd67997c643 (xen.git)
> 
> But I still don't undertand this.

I think that means the MiniOS would hit a page fault and allocate
a page. I don't know if EFI drivers have this concept?
> 
> > > +      *(CHAR8 *)(Data + (Request->seg[Index].first_sect << 9)) = 0;
> > > +      MemoryFence ();

If the EFI 'things' that use the BlockIO drivers allocate an page
for read, then there is no need for this.

> > > +    }
> > > +    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 ?
> > 
> > Maybe for later versions. I think this is OK for right now, thought
> > it will mean we can only do one I/O .. and have then to wait
> > until it is completed.
> > 
> > That limititation should be mentioned in the commit description.
> 
> That right, right now, it's only one IO at a time. I think my comment is
> more to tell me that Callback is not really one, and it could be replace
> by something more Uefi, an event.
> 
> > > +  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);
> > 
> > How do we make sure that there aren't multiple threads
> > calling this?
> 
> Not possible yet.
> 
> > > +  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 */
> > 
> > Uh, how does that happen?
> 
> That an original comment, I don't think it's possible yet in ovmf.
> 
> > > +        break;
> > > +      }
> > > +    }
> > > +
> > > +    RING_FINAL_CHECK_FOR_RESPONSES (&Dev->Ring, More);
> > > +  } while (More != 0);
> > > +}
> 
> -- 
> Anthony PERARD