OvmfPkg/VirtioFsDxe: implement the wrapper function for FUSE_FORGET

Add the VirtioFsFuseForget() function, for sending the FUSE_FORGET command
to the Virtio Filesystem device.

This is an unusual command in that it doesn't generate any response from
the FUSE server.

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: <20201216211125.19496-13-lersek@redhat.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>

OvmfPkg/Include/IndustryStandard/VirtioFs.h

@@ -85,6 +85,7 @@ typedef struct {
 // FUSE operation codes.
 //
 typedef enum {
+  VirtioFsFuseOpForget      =  2,
   VirtioFsFuseOpRelease     = 18,
   VirtioFsFuseOpInit        = 26,
   VirtioFsFuseOpOpenDir     = 27,
@@ -112,6 +113,13 @@ typedef struct {
   UINT64 Unique;
 } VIRTIO_FS_FUSE_RESPONSE;
 
+//
+// Header for VirtioFsFuseOpForget.
+//
+typedef struct {
+  UINT64 NumberOfLookups;
+} VIRTIO_FS_FUSE_FORGET_REQUEST;
+
 //
 // Header for VirtioFsFuseOpRelease and VirtioFsFuseOpReleaseDir.
 //