OvmfPkg/VirtioFsDxe: implement EFI_FILE_PROTOCOL.GetPosition, .SetPosition

Using the functions introduced previously, we can now implement
VirtioFsSimpleFileGetPosition() and VirtioFsSimpleFileSetPosition().

Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3097
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20201216211125.19496-32-lersek@redhat.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>

OvmfPkg/VirtioFsDxe/SimpleFsGetPosition.c

@@ -16,5 +16,12 @@ VirtioFsSimpleFileGetPosition (
      OUT UINT64            *Position
   )
 {
-  return EFI_DEVICE_ERROR;
+  VIRTIO_FS_FILE *VirtioFsFile;
+
+  VirtioFsFile = VIRTIO_FS_FILE_FROM_SIMPLE_FILE (This);
+  if (VirtioFsFile->IsDirectory) {
+    return EFI_UNSUPPORTED;
+  }
+  *Position = VirtioFsFile->FilePosition;
+  return EFI_SUCCESS;
 }

OvmfPkg/VirtioFsDxe/SimpleFsOpen.c

@@ -479,6 +479,7 @@ VirtioFsSimpleFileOpen (
   NewVirtioFsFile->IsOpenForWriting       = OpenForWriting;
   NewVirtioFsFile->OwnerFs                = VirtioFs;
   NewVirtioFsFile->CanonicalPathname      = NewCanonicalPath;
+  NewVirtioFsFile->FilePosition           = 0;
   NewVirtioFsFile->NodeId                 = NewNodeId;
   NewVirtioFsFile->FuseHandle             = NewFuseHandle;
 

OvmfPkg/VirtioFsDxe/SimpleFsOpenVolume.c

@@ -72,6 +72,7 @@ VirtioFsOpenVolume (
   VirtioFsFile->IsOpenForWriting       = FALSE;
   VirtioFsFile->OwnerFs                = VirtioFs;
   VirtioFsFile->CanonicalPathname      = CanonicalPathname;
+  VirtioFsFile->FilePosition           = 0;
   VirtioFsFile->NodeId                 = VIRTIO_FS_FUSE_ROOT_DIR_NODE_ID;
   VirtioFsFile->FuseHandle             = RootDirHandle;
 

OvmfPkg/VirtioFsDxe/SimpleFsSetPosition.c

@@ -16,5 +16,43 @@ VirtioFsSimpleFileSetPosition (
   IN UINT64            Position
   )
 {
-  return EFI_DEVICE_ERROR;
+  VIRTIO_FS_FILE                     *VirtioFsFile;
+  VIRTIO_FS                          *VirtioFs;
+  EFI_STATUS                         Status;
+  VIRTIO_FS_FUSE_ATTRIBUTES_RESPONSE FuseAttr;
+
+  VirtioFsFile = VIRTIO_FS_FILE_FROM_SIMPLE_FILE (This);
+
+  //
+  // Directories can only be rewound, per spec.
+  //
+  if (VirtioFsFile->IsDirectory) {
+    if (Position != 0) {
+      return EFI_UNSUPPORTED;
+    }
+    VirtioFsFile->FilePosition = 0;
+    return EFI_SUCCESS;
+  }
+
+  //
+  // Regular file.
+  //
+  if (Position < MAX_UINT64) {
+    //
+    // Caller is requesting absolute file position.
+    //
+    VirtioFsFile->FilePosition = Position;
+    return EFI_SUCCESS;
+  }
+
+  //
+  // Caller is requesting a seek to EOF.
+  //
+  VirtioFs = VirtioFsFile->OwnerFs;
+  Status = VirtioFsFuseGetAttr (VirtioFs, VirtioFsFile->NodeId, &FuseAttr);
+  if (EFI_ERROR (Status)) {
+    return Status;
+  }
+  VirtioFsFile->FilePosition = FuseAttr.Size;
+  return EFI_SUCCESS;
 }

OvmfPkg/VirtioFsDxe/VirtioFsDxe.h

@@ -139,6 +139,7 @@ typedef struct {
   VIRTIO_FS         *OwnerFs;
   LIST_ENTRY        OpenFilesEntry;
   CHAR8             *CanonicalPathname;
+  UINT64            FilePosition;
   //
   // In the FUSE wire protocol, every request except FUSE_INIT refers to a
   // file, namely by the "VIRTIO_FS_FUSE_REQUEST.NodeId" field; that is, by the