OvmfPkg/VirtioFsDxe: implement virtio device (un)initialization

Add the VirtioFsInit(), VirtioFsUninit(), and VirtioFsExitBoot()
functions.

In VirtioFsInit():

- Verify the host-side config of the virtio-fs device.

- Save the filesystem label ("tag") for later, from the configuration area
  of the virtio-fs device.

- Save the virtio queue size for later as well.

- Set up the virtio ring for sending requests.

In VirtioFsUninit():

- Reset the device.

- Tear down the virtio ring.

In VirtioFsExitBoot():

- Reset the device.

With this patch, the UEFI connect / disconnect controller operations
involve virtio setup / teardown; they are visible in the virtio-fs
daemon's log file. The virtiofsd log also confirms the device reset in
VirtioFsExitBoot(), when an OS is booted while the virtio-fs device is
bound.

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: <20201216211125.19496-5-lersek@redhat.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>

OvmfPkg/Include/IndustryStandard/VirtioFs.h

@@ -0,0 +1,52 @@
+/** @file
+  Type and macro definitions specific to the Virtio Filesystem device.
+
+  At the time of this writing, the latest released Virtio specification (v1.1)
+  does not include the virtio-fs device. The development version of the
+  specification defines it however; see the latest version at
+  <https://github.com/oasis-tcs/virtio-spec/blob/87fa6b5d8155/virtio-fs.tex>.
+
+  This header file is minimal, and only defines the types and macros that are
+  necessary for the OvmfPkg implementation.
+
+  Copyright (C) 2020, Red Hat, Inc.
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+**/
+
+#ifndef VIRTIO_FS_H_
+#define VIRTIO_FS_H_
+
+#include <IndustryStandard/Virtio.h>
+
+//
+// Lowest numbered queue for sending normal priority requests.
+//
+#define VIRTIO_FS_REQUEST_QUEUE 1
+
+//
+// Number of bytes in the "VIRTIO_FS_CONFIG.Tag" field.
+//
+#define VIRTIO_FS_TAG_BYTES 36
+
+//
+// Device configuration layout.
+//
+#pragma pack (1)
+typedef struct {
+  //
+  // The Tag field can be considered the filesystem label, or a mount point
+  // hint. It is UTF-8 encoded, and padded to full size with NUL bytes. If the
+  // encoded bytes take up the entire Tag field, then there is no NUL
+  // terminator.
+  //
+  UINT8 Tag[VIRTIO_FS_TAG_BYTES];
+  //
+  // The total number of request virtqueues exposed by the device (i.e.,
+  // excluding the "hiprio" queue).
+  //
+  UINT32 NumReqQueues;
+} VIRTIO_FS_CONFIG;
+#pragma pack ()
+
+#endif // VIRTIO_FS_H_