OvmfPkg/VirtioFsDxe: DriverBinding: open VirtioDevice, install SimpleFs

Complete the Supported, Start, and Stop member functions of
EFI_DRIVER_BINDING_PROTOCOL sufficiently for exercising the UEFI driver
model:

- bind virtio-fs devices,

- produce placeholder EFI_SIMPLE_FILE_SYSTEM_PROTOCOL instances on them.

On the "TO_START" (= Virtio) side, the VirtioFsBindingSupported() function
verifies the Virtio subsystem ID for the virtio-fs device (decimal 26 --
see
<https://github.com/oasis-tcs/virtio-spec/blob/87fa6b5d8155/virtio-fs.tex>).
Beyond that, no actual Virtio setup is performed for now. Those bits are
going to be implemented later in this series.

On the "BY_START" (= UEFI filesystem) side, the VirtioFsOpenVolume()
function -- which is the sole EFI_SIMPLE_FILE_SYSTEM_PROTOCOL member
function -- is a stub; it always returns EFI_NO_MEDIA, for now.

The "CONNECT", "DISCONNECT", and "MAP -R" UEFI Shell commands can be used
to test this patch.

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: <20201216211125.19496-4-lersek@redhat.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>

OvmfPkg/VirtioFsDxe/VirtioFsDxe.h

@@ -0,0 +1,52 @@
+/** @file
+  Internal macro definitions, type definitions, and function declarations for
+  the Virtio Filesystem device driver.
+
+  Copyright (C) 2020, Red Hat, Inc.
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+**/
+
+#ifndef VIRTIO_FS_DXE_H_
+#define VIRTIO_FS_DXE_H_
+
+#include <Base.h>                      // SIGNATURE_64()
+#include <Library/DebugLib.h>          // CR()
+#include <Protocol/SimpleFileSystem.h> // EFI_SIMPLE_FILE_SYSTEM_PROTOCOL
+#include <Protocol/VirtioDevice.h>     // VIRTIO_DEVICE_PROTOCOL
+
+#define VIRTIO_FS_SIG SIGNATURE_64 ('V', 'I', 'R', 'T', 'I', 'O', 'F', 'S')
+
+//
+// Main context structure, expressing an EFI_SIMPLE_FILE_SYSTEM_PROTOCOL
+// interface on top of the Virtio Filesystem device.
+//
+typedef struct {
+  //
+  // Parts of this structure are initialized / torn down in various functions
+  // at various call depths. The table to the right should make it easier to
+  // track them.
+  //
+  //                              field         init function       init depth
+  //                              -----------   ------------------  ----------
+  UINT64                          Signature; // DriverBindingStart  0
+  VIRTIO_DEVICE_PROTOCOL          *Virtio;   // DriverBindingStart  0
+  EFI_SIMPLE_FILE_SYSTEM_PROTOCOL SimpleFs;  // DriverBindingStart  0
+} VIRTIO_FS;
+
+#define VIRTIO_FS_FROM_SIMPLE_FS(SimpleFsReference) \
+  CR (SimpleFsReference, VIRTIO_FS, SimpleFs, VIRTIO_FS_SIG);
+
+//
+// EFI_SIMPLE_FILE_SYSTEM_PROTOCOL member functions for the Virtio Filesystem
+// driver.
+//
+
+EFI_STATUS
+EFIAPI
+VirtioFsOpenVolume (
+  IN  EFI_SIMPLE_FILE_SYSTEM_PROTOCOL *This,
+  OUT EFI_FILE_PROTOCOL               **Root
+  );
+
+#endif // VIRTIO_FS_DXE_H_