OvmfPkg/VirtioFsDxe: add EFI_FILE_INFO cache fields to VIRTIO_FS_FILE

For reading through a directory stream with tolerable performance, we'll
have to call FUSE_READDIRPLUS each time with such a buffer that can
deliver a good number of variable size records
(VIRTIO_FS_FUSE_DIRENTPLUS_RESPONSE elements). Every time we'll do that,
we'll turn the whole bunch into an array of EFI_FILE_INFOs immediately.
EFI_FILE_PROTOCOL.Read() invocations (on directories) will be served from
this EFI_FILE_INFO cache.

Add the fields for the EFI_FILE_INFO cache to VIRTIO_FS_FILE:
- initialize them in Open() and OpenVolume(),
- release the cache in Close() and Delete(),
- also release the cache when the directory is rewound, in SetPosition().

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: <20201216211125.19496-36-lersek@redhat.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>

OvmfPkg/VirtioFsDxe/SimpleFsSetPosition.c

@@ -7,6 +7,8 @@
   SPDX-License-Identifier: BSD-2-Clause-Patent
 **/
 
+#include <Library/MemoryAllocationLib.h> // FreePool()
+
 #include "VirtioFsDxe.h"
 
 EFI_STATUS
@@ -31,6 +33,13 @@ VirtioFsSimpleFileSetPosition (
       return EFI_UNSUPPORTED;
     }
     VirtioFsFile->FilePosition = 0;
+    if (VirtioFsFile->FileInfoArray != NULL) {
+      FreePool (VirtioFsFile->FileInfoArray);
+      VirtioFsFile->FileInfoArray = NULL;
+    }
+    VirtioFsFile->SingleFileInfoSize = 0;
+    VirtioFsFile->NumFileInfo        = 0;
+    VirtioFsFile->NextFileInfo       = 0;
     return EFI_SUCCESS;
   }