MdePkg: Add EFI_LOAD_OPTION definition.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Felix Poludov <Felixp@ami.com>
Reviewed-by: Kinney Michael <michael.d.kinney@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17390 6f19259b-4bc3-4df7-8a09-765794883524

MdePkg/Include/Uefi/UefiSpec.h

@@ -2000,6 +2000,55 @@ EFI_STATUS
   IN  EFI_SYSTEM_TABLE             *SystemTable
   );
 
+//
+// EFI Load Option. This data structure describes format of UEFI boot option variables.
+//
+// NOTE: EFI Load Option is a byte packed buffer of variable length fields.
+// The first two fields have fixed length. They are declared as members of the
+// EFI_LOAD_OPTION structure. All the other fields are variable length fields.
+// They are listed in the comment block below for reference purposes.
+//
+#pragma pack(1)
+typedef struct _EFI_LOAD_OPTION {
+  ///
+  /// The attributes for this load option entry. All unused bits must be zero
+  /// and are reserved by the UEFI specification for future growth.
+  ///
+  UINT32                           Attributes;
+  ///
+  /// Length in bytes of the FilePathList. OptionalData starts at offset
+  /// sizeof(UINT32) + sizeof(UINT16) + StrSize(Description) + FilePathListLength
+  /// of the EFI_LOAD_OPTION descriptor.
+  ///
+  UINT16                           FilePathListLength;
+  ///
+  /// The user readable description for the load option.
+  /// This field ends with a Null character.
+  ///
+  // CHAR16                        Description[];
+  ///
+  /// A packed array of UEFI device paths. The first element of the array is a
+  /// device path that describes the device and location of the Image for this
+  /// load option. The FilePathList[0] is specific to the device type. Other
+  /// device paths may optionally exist in the FilePathList, but their usage is
+  /// OSV specific. Each element in the array is variable length, and ends at
+  /// the device path end structure. Because the size of Description is
+  /// arbitrary, this data structure is not guaranteed to be aligned on a
+  /// natural boundary. This data structure may have to be copied to an aligned
+  /// natural boundary before it is used.
+  ///
+  // EFI_DEVICE_PATH_PROTOCOL      FilePathList[];
+  ///
+  /// The remaining bytes in the load option descriptor are a binary data buffer
+  /// that is passed to the loaded image. If the field is zero bytes long, a
+  /// NULL pointer is passed to the loaded image. The number of bytes in
+  /// OptionalData can be computed by subtracting the starting offset of
+  /// OptionalData from total size in bytes of the EFI_LOAD_OPTION.
+  ///
+  // UINT8                         OptionalData[];
+} EFI_LOAD_OPTION;
+#pragma pack()
+
 //
 // EFI Load Options Attributes
 //