1、概述

在主板上电后，UEFI会将HW信息包括， CPU、Memory、FW、PM等信息以SMBIOS table形式上存储到一段内存区域中，进入OS后，OS通过解析该段内存即可获取相关配置。
SMBIOS是通过DXE驱动加载到系统表的，入口函数为SmbiosDriverEntryPoint，该驱动程序生成一个实例。实例包含了增加、更新、移除、获取 SMBIOS的函数，入口函数还初始化数据链表和句柄头部链表。最后实现的实例安装到新的句柄上，在DXE阶段调用。

EFI_STATUS
EFIAPI
SmbiosDriverEntryPoint (
  IN EFI_HANDLE           ImageHandle,
  IN EFI_SYSTEM_TABLE     *SystemTable
  )
{
  EFI_STATUS            Status;

  mPrivateData.Signature                = SMBIOS_INSTANCE_SIGNATURE;
  mPrivateData.Smbios.Add               = SmbiosAdd;
  mPrivateData.Smbios.UpdateString      = SmbiosUpdateString;
  mPrivateData.Smbios.Remove            = SmbiosRemove;
  mPrivateData.Smbios.GetNext           = SmbiosGetNext;
  mPrivateData.Smbios.MajorVersion      = (UINT8) (PcdGet16 (PcdSmbiosVersion) >> 8);
  mPrivateData.Smbios.MinorVersion      = (UINT8) (PcdGet16 (PcdSmbiosVersion) & 0x00ff);

  InitializeListHead (&mPrivateData.DataListHead);
  InitializeListHead (&mPrivateData.AllocatedHandleListHead);
  EfiInitializeLock (&mPrivateData.DataLock, TPL_NOTIFY);
  
  //
  // Make a new handle and install the protocol
  //
  mPrivateData.Handle = NULL;
  Status = gBS->InstallProtocolInterface (
                  &mPrivateData.Handle,
                  &gEfiSmbiosProtocolGuid,
                  EFI_NATIVE_INTERFACE,
                  &mPrivateData.Smbios
                  );

  return Status;
}

2、创建表结构

SmbiosCreateTable (
  OUT VOID    **TableEntryPointStructure
  )
  {
  .....
  EntryPointStructureData.MajorVersion  = mPrivateData.Smbios.MajorVersion;
  EntryPointStructureData.MinorVersion  = mPrivateData.Smbios.MinorVersion;
  EntryPointStructureData.SmbiosBcdRevision = (UINT8) ((PcdGet16 (PcdSmbiosVersion) >> 4) & 0xf0) | (UINT8) (PcdGet16 (PcdSmbiosVersion) & 0x0f);
  PhysicalAddress = 0xffffffff;
  Status = gBS->AllocatePages (
                    AllocateMaxAddress,
                    EfiRuntimeServicesData,
                    EFI_SIZE_TO_PAGES (sizeof (SMBIOS_TABLE_ENTRY_POINT)),
                    &PhysicalAddress
                    );
  ....
  }

创建表结构的主要功能为
1、根据EPS表结构填充字段

位置	名称	长度	描述
00H	关键字	4BYTE	固定是”SM”
04H	校验和	1BYTE	用于校验数据
05H	表结构长度	1BYTE	Entry Point Structure 表的长度
06H	Major 版本号	1BYTE	用于判断SMBIOS 版本
07H	Minor 版本号	1BYTE	用于判断SMBIOS 版本
08H	表结构大小	2BYTE	用于即插即用接口方法获得数据表结构长度
0AH	EPS 修正	1BYTE
0B-0FH	格式区域	5BYTE	存放解释EPS 修正的信息
10H	关键字	5BYTE	固定为“DMI”
15H	校验和	1BYTE	Intermediate Entry Point Structure (IEPS)的校验和
16H	结构表长度	2BYTE	SMBIOS 结构表的长度
18H	结构表地址	4BYTE	SMBIOS 结构表的真实内存位置
1CH	结构表个数	2BYTE	SMBIOS 结构表数目
1EH	Smbios BCD 修正	1BYTE

与SMBIOS的SMBIOS_TABLE_ENTRY_POINT结构体对应起来

typedef struct {
  UINT8   AnchorString[4];
  UINT8   EntryPointStructureChecksum;
  UINT8   EntryPointLength;
  UINT8   MajorVersion;
  UINT8   MinorVersion;
  UINT16  MaxStructureSize;
  UINT8   EntryPointRevision;
  UINT8   FormattedArea[5];
  UINT8   IntermediateAnchorString[5];
  UINT8   IntermediateChecksum;
  UINT16  TableLength;
  UINT32  TableAddress;
  UINT16  NumberOfSmbiosStructures;
  UINT8   SmbiosBcdRevision;
} SMBIOS_TABLE_ENTRY_POINT;

2、创建表头部

位置	名称	长度	描述
00H	TYPE 号	1BYTE	结构的TYPE 号
01H	长度	1BYTE	本结构的长度，就此TYPE 号的结构而言
02H	句柄	2BYTE	用于获得本SMBIOS 结构，其值不定

 EndStructure.Header.Type = SMBIOS_TYPE_END_OF_TABLE;
  EndStructure.Header.Length = (UINT8) sizeof (EFI_SMBIOS_TABLE_HEADER);
  EndStructure.Header.Handle = SmbiosHandle;

3 增加SMBIOS表

mPrivateData.Smbios.Add = SmbiosAdd;

EFI_STATUS
EFIAPI
SmbiosAdd (
  IN CONST EFI_SMBIOS_PROTOCOL  *This,
  IN EFI_HANDLE                 ProducerHandle, OPTIONAL
  IN OUT EFI_SMBIOS_HANDLE      *SmbiosHandle,
  IN EFI_SMBIOS_TABLE_HEADER    *Record
  )
   Add an SMBIOS record.

  @param  This                  The EFI_SMBIOS_PROTOCOL instance.
  @param  ProducerHandle        The handle of the controller or driver associated with the SMBIOS information. NULL
                                means no handle.
  @param  SmbiosHandle          On entry, the handle of the SMBIOS record to add. If FFFEh, then a unique handle
                                will be assigned to the SMBIOS record. If the SMBIOS handle is already in use,
                                EFI_ALREADY_STARTED is returned and the SMBIOS record is not updated.
  @param  Record                The data for the fixed portion of the SMBIOS record. The format of the record is
                                determined by EFI_SMBIOS_TABLE_HEADER.Type. The size of the formatted area is defined 
                                by EFI_SMBIOS_TABLE_HEADER.Length and either followed by a double-null (0x0000) or 
                                a set of null terminated strings and a null.

  @retval EFI_SUCCESS           Record was added.
  @retval EFI_OUT_OF_RESOURCES  Record was not added due to lack of system resources.
  @retval EFI_ALREADY_STARTED   The SmbiosHandle passed in was already in use.

1、核实SmbiosHandle是否在使用中
2、计算record的大小和字符数字
找到1个0，是一个字段的长度
找到两个0，就是一条record的大小
3、分配record的内存空间
TotalSize = sizeof (EFI_SMBIOS_ENTRY) + sizeof (EFI_SMBIOS_RECORD_HEADER) + StructureSize;
4、构建句柄入口并且增加到链表中

 HandleEntry->Signature     = SMBIOS_HANDLE_ENTRY_SIGNATURE;
  HandleEntry->SmbiosHandle  = *SmbiosHandle;
  InsertTailList(&Private->AllocatedHandleListHead, &HandleEntry->Link);

5、构建record 的头结构并且增加到内部的链表中

InternalRecord->Version     = EFI_SMBIOS_RECORD_HEADER_VERSION;
  InternalRecord->HeaderSize  = (UINT16) sizeof (EFI_SMBIOS_RECORD_HEADER);
  InternalRecord->RecordSize  = RecordSize;
  InternalRecord->ProducerHandle = ProducerHandle;
  InternalRecord->NumberOfStrings = NumberOfStrings;
  SmbiosEntry->Signature    = EFI_SMBIOS_ENTRY_SIGNATURE;
  SmbiosEntry->RecordHeader = InternalRecord;
  SmbiosEntry->RecordSize   = TotalSize;
  SmbiosEntry->Smbios32BitTable = Smbios32BitTable;
  SmbiosEntry->Smbios64BitTable = Smbios64BitTable;
  InsertTailList (&Private->DataListHead, &SmbiosEntry->Link);

6、安装SMBIOS表到系统表中

typedef
EFI_STATUS
(EFIAPI *EFI_INSTALL_CONFIGURATION_TABLE)(
  IN EFI_GUID                 *Guid,
  IN VOID                     *Table
  );
  Adds, updates, or removes a configuration table entry from the EFI System Table.

  @param[in]  Guid              A pointer to the GUID for the entry to add, update, or remove.
  @param[in]  Table             A pointer to the configuration table for the entry to add, update, or
                                remove. May be NULL.

  @retval EFI_SUCCESS           The (Guid, Table) pair was added, updated, or removed.
  @retval EFI_NOT_FOUND         An attempt was made to delete a nonexistent entry.
  @retval EFI_INVALID_PARAMETER Guid is NULL.
  @retval EFI_OUT_OF_RESOURCES  There is not enough memory available to complete the operation.

4、获得SMBIOS Record

mPrivateData.Smbios.GetNext = SmbiosGetNext;

EFI_STATUS
EFIAPI
GetNextSmbiosRecord (
  IN CONST EFI_SMBIOS_PROTOCOL         *This,
  IN OUT EFI_SMBIOS_ENTRY              **CurrentSmbiosEntry,
  OUT EFI_SMBIOS_TABLE_HEADER          **Record
  )

1、CurrentSmbiosEntry，在退出时，指针指向包含SMBIOS记录信息的入口地址，如果CurrentSmbiosEntry指针在入口时为空，第一个smbios 的入口地址将被返回。
2、Record，在退出时，指向SMBIOS记录，该记录由格式化区域组成，然后是
无格式的区域。无格式区域可选地包含文本字符串。
通过链表遍历的方法获得SMBIOS record

5、更新或移除SMBIOS Record

mPrivateData.Smbios.UpdateString = SmbiosUpdateString;
mPrivateData.Smbios.Remove = SmbiosRemove;

更新：重新构建InternalRecord，再加载到系统表

6、增加一条SMBIOS table记录

smbios 驱动加载完成，怎样实际增加一条type0/type1/type2…记录
1、先根据gEfiSmbiosProtocolGuid 获得mSmbios接口
Status = gBS->LocateProtocol(&gEfiSmbiosProtocolGuid, NULL, (VOID **)&mSmbios);
2、再通过接口中add 函数加载到系统表中
EFI_SMBIOS_PROTOCOL *mSmbios;
Status = mSmbios->Add (
mSmbios,
NULL,
&SmbiosHandle,
(EFI_SMBIOS_TABLE_HEADER *)SmbiosRecord
);