> For the complete documentation index, see [llms.txt](https://bob-mcd-team.gitbook.io/uefi/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://bob-mcd-team.gitbook.io/uefi/uefi-development/shell-app/14.getnextvariablename-api.md).

# 14.gRT->GetNextVariableName API를 사용하여 모든 변수 이름 및 GUID 가져오기

이번 장에서는 런타임 변수를 모두 출력해보는 실습을 한다.

이를 위해서는 EFI Runtime Services의 `GetNextVariableName()` API 함수를 사용해야 한다.

```
GetNextVariableName()

Summary:
Enumerates the current variable names.

Prototype:
typedef
EFI_STATUS
GetNextVariableName (
 IN OUT UINTN *VariableNameSize,
 IN OUT CHAR16 *VariableName,
 IN OUT EFI_GUID *VendorGuid
 );

Parameters:
VariableNameSize 	The size of the VariableName buffer. The size must be large
			enough to fit input string supplied in VariableName buffer.
VariableName 		On input, supplies the last VariableName that was returned by
			GetNextVariableName(). On output, returns the Nullterminated string
			of the current variable.
VendorGuid 		On input, supplies the last VendorGuid that was returned by
			GetNextVariableName(). On output, returns the VendorGuid
			of the current variable.

Description
GetNextVariableName() is called multiple times to retrieve the VariableName and VendorGuid of all
variables currently available in the system. On each call to GetNextVariableName() the previous
results are passed into the interface, and on output the interface returns the next variable name data.
When the entire variable list has been returned, the error EFI_NOT_FOUND is returned.

Note that if EFI_BUFFER_TOO_SMALL is returned, the VariableName buffer was too small for the next
variable. When such an error occurs, the VariableNameSize is updated to reflect the size of buffer
needed. In all cases when calling GetNextVariableName() the VariableNameSize must not exceed the
actual buffer size that was allocated for VariableName. The VariableNameSize must not be smaller the size
of the variable name string passed to GetNextVariableName() on input in the VariableName buffer.

To start the search, a Null-terminated string is passed in VariableName; that is, VariableName is a pointer
to a Null character. This is always done on the initial call to GetNextVariableName(). When
VariableName is a pointer to a Null character, VendorGuid is ignored.


Status Codes Returned:
EFI_SUCCESS 		The function completed successfully.
EFI_NOT_FOUND 		The next variable was not found.
EFI_BUFFER_TOO_SMALL 	The VariableNameSize is too small for the result.
			VariableNameSize has been updated with the size needed to complete the request.
...
```

이전에 `gST`/`gBS`를 얻기 위해 파일에 `#include <Library/UefiBootServicesTableLib.h>`를 포함했다. EFI Runtime Services Table에 대한 바로가기를 얻으려면 비슷한 헤더파일을 추가해야 한다.

```
#include <Library/UefiRuntimeServicesTableLib.h>
```

{% embed url="<https://github.com/tianocore/edk2/blob/master/MdePkg/Library/UefiRuntimeServicesTableLib/UefiRuntimeServicesTableLib.c>" %}

위 파일을 보면 라이브러리 생성자 호출 때 `gRT = SystemTable->RuntimeServices;`로 채워지는 `extern EFI_RUNTIME_SERVICES *gRT;`만 단순히 추가해준다.

UEFI 스펙에 따르면 검색을 하려면 Null (=0)과 같은 1개의 문자로 문자열을 생성해야 한다고 한다.이러한 문자열을 생성하기 위해 `AllocateZeroPool`함수를 사용한다.

```c
UINTN VariableNameSize = sizeof (CHAR16);
CHAR16* VariableName = AllocateZeroPool(sizeof(CHAR16));
```

`AllocateZeroPool` 은 UEFI 스펙에서 정의된 기능이 아니고 EDKII의 MemoryAllocationLib에서 사용자를 편하게 해주기 위해 만든 기능이다.

{% embed url="<https://github.com/tianocore/edk2/blob/master/MdePkg/Library/PeiMemoryAllocationLib/MemoryAllocationLib.c>" %}

```c
/**
  Allocates and zeros a buffer of type EfiBootServicesData.
   ...
  @param  AllocationSize        The number of bytes to allocate and zero.

  @return A pointer to the allocated buffer or NULL if allocation fails.
**/

VOID *
EFIAPI
AllocateZeroPool (
  IN UINTN  AllocationSize
  )
```

이 문자열은 변수 이름을 저장하기에 충분히 크지 않을 것이므로 적어도 첫 번째 호출에서는 확실하게 `EFI_BUFFER_TOO_SMALL`을 반환할 것이다.

이 경우 버퍼를 재할당해야 하는데 `ReallocatePool` 함수로 이를 수행할 수 있다.

`ReallocatePool`또한 EDKII의 MemoryAllocationLib에서 만들어진 함수이다.

{% embed url="<https://github.com/tianocore/edk2/blob/master/MdePkg/Library/PeiMemoryAllocationLib/MemoryAllocationLib.c>" %}

```c
/**
  Reallocates a buffer of type EfiBootServicesData.
   ...
  @param  OldSize        The size, in bytes, of OldBuffer.
  @param  NewSize        The size, in bytes, of the buffer to reallocate.
  @param  OldBuffer      The buffer to copy to the allocated buffer.  This is an optional
                         parameter that may be NULL.
  @return A pointer to the allocated buffer or NULL if allocation fails.
**/

VOID *
EFIAPI
ReallocatePool (
  IN UINTN  OldSize,
  IN UINTN  NewSize,
  IN VOID   *OldBuffer  OPTIONAL
  )
```

이제 `ListVariables`라는 애플리케이션을 만들어서 첫 번째 변수를 출력해보자.

```c
#include <Library/UefiBootServicesTableLib.h>
#include <Library/UefiLib.h>

#include <Library/MemoryAllocationLib.h>
#include <Library/UefiRuntimeServicesTableLib.h>

INTN EFIAPI ShellAppMain(IN UINTN Argc, IN CHAR16 **Argv)
{
  EFI_GUID VendorGuid;
  UINTN VariableNameSize = sizeof (CHAR16);
  CHAR16* VariableName = AllocateZeroPool(sizeof(CHAR16));
  if (VariableName == NULL) {
    Print(L"Error on AllocateZeroPool call\n");
    return EFI_OUT_OF_RESOURCES;
  }

  UINTN VariableNameSizeOld = VariableNameSize;
  EFI_STATUS Status = gRT->GetNextVariableName(&VariableNameSize, VariableName, &VendorGuid);
  if (Status == EFI_BUFFER_TOO_SMALL) {
    VariableName = ReallocatePool(VariableNameSizeOld, VariableNameSize, VariableName);
    if (VariableName == NULL) {
      return EFI_OUT_OF_RESOURCES;
    }
    Status = gRT->GetNextVariableName(&VariableNameSize, VariableName, &VendorGuid);
    if (Status == EFI_SUCCESS) {
      Print(L"%g: %s\n", VendorGuid, VariableName);
    } else {
      Print(L"Error on 'gRT->GetNextVariableName' call: %s\n", Status);
      return Status;
    }
  } else {
    Print(L"Error on 'gRT->GetNextVariableName' call: %s\n", Status);
    return Status;
  }
  FreePool(VariableName);
  return EFI_SUCCESS;
}
```

빌드 후에 OVMF로 실행해보면 다음과 같은 결과를 얻을 수 있다.

```
FS0:\> ListVariables.efi
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: OsIndicationsSupported
```

이제 사용되는 모든 변수를 출력하는 반복문을 작성하여 모든 변수를 출력해보자.

```c
#include <Library/UefiBootServicesTableLib.h>
#include <Library/UefiLib.h>

#include <Library/MemoryAllocationLib.h>
#include <Library/UefiRuntimeServicesTableLib.h>

INTN EFIAPI ShellAppMain(IN UINTN Argc, IN CHAR16 **Argv)
{
  EFI_GUID VendorGuid;
  UINTN VariableNameSize = sizeof (CHAR16);
  CHAR16* VariableName = AllocateZeroPool(sizeof(CHAR16));
  if (VariableName == NULL) {
    rint(L"Error on AllocateZeroPool call\n");
    return EFI_OUT_OF_RESOURCES;
  }

  while (TRUE)
  {
    UINTN VariableNameSizeOld = VariableNameSize;
    EFI_STATUS Status = gRT->GetNextVariableName(&VariableNameSize, VariableName, &VendorGuid);
    if (Status == EFI_SUCCESS) {
      Print(L"%g: %s\n", VendorGuid, VariableName);
    } else if (Status == EFI_BUFFER_TOO_SMALL) {
      VariableName = ReallocatePool(VariableNameSizeOld, VariableNameSize, VariableName);
      if (VariableName == NULL) {
        Print(L"Error on ReallocatePool call\n");
        return EFI_OUT_OF_RESOURCES;
      }
      Status = gRT->GetNextVariableName(&VariableNameSize, VariableName, &VendorGuid);
      if (Status == EFI_SUCCESS) {
        Print(L"%g: %s\n", VendorGuid, VariableName);
      } else {
        Print(L"Error on 'gRT->GetNextVariableName' call: %s\n", Status);
        return Status;
      }
    } else if (Status == EFI_NOT_FOUND) {
      FreePool(VariableName);
      return EFI_SUCCESS;
    } else {
      Print(L"Error on 'gRT->GetNextVariableName' call: %s\n", Status);
      return Status;
    }
  }
  return EFI_SUCCESS;
}
```

while(TRUE) 반복문 안에서 `gRT->GetNextVariableName`함수를 계속 실행하여 반환된 EFI\_STATUS코드를 구분한다.

* `EFI_SUCCESS`는 변수를 성공적으로 획득했음을 나타내므로 그냥 출력하면 된다.
* `EFI_BUFFER_TOO_SMALL`은 배열을 `ReAllocatePool`을 호출해 크기를 늘리고 다시 `gRT->GetNextVariableName`를 호출해야 함을 의미한다.
* `EFI_NOT_FOUND`는 우리가 모든 변수를 파싱하여 멈춰야 한다는 것을 의미한다.
* 다른 상태에서는 단순 오류로 출력하고 반환한다.

이제 우리 프로그램을 OVMF에서 실행하면 다음과 같이 출력된다.

```
FS0:\> ListVariables.efi
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: OsIndicationsSupported
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: BootOptionSupport
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: LangCodes
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: PlatformLangCodes
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: PlatformRecovery0000
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: ConOutDev
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: ErrOutDev
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: ConInDev
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: BootCurrent
158DEF5A-F656-419C-B027-7A3192C079D2: path
158DEF5A-F656-419C-B027-7A3192C079D2: nonesting
0053D9D6-2659-4599-A26B-EF4536E631A9: cat
0053D9D6-2659-4599-A26B-EF4536E631A9: cd..
0053D9D6-2659-4599-A26B-EF4536E631A9: cd\
0053D9D6-2659-4599-A26B-EF4536E631A9: copy
0053D9D6-2659-4599-A26B-EF4536E631A9: del
0053D9D6-2659-4599-A26B-EF4536E631A9: dir
0053D9D6-2659-4599-A26B-EF4536E631A9: md
0053D9D6-2659-4599-A26B-EF4536E631A9: mem
0053D9D6-2659-4599-A26B-EF4536E631A9: mount
0053D9D6-2659-4599-A26B-EF4536E631A9: move
0053D9D6-2659-4599-A26B-EF4536E631A9: ren
158DEF5A-F656-419C-B027-7A3192C079D2: profiles
158DEF5A-F656-419C-B027-7A3192C079D2: uefishellsupport
158DEF5A-F656-419C-B027-7A3192C079D2: uefishellversion
158DEF5A-F656-419C-B027-7A3192C079D2: uefiversion
158DEF5A-F656-419C-B027-7A3192C079D2: cwd
158DEF5A-F656-419C-B027-7A3192C079D2: debuglasterror
158DEF5A-F656-419C-B027-7A3192C079D2: lasterror
59324945-EC44-4C0D-B1CD-9DB139DF070C: Attempt 1
59324945-EC44-4C0D-B1CD-9DB139DF070C: Attempt 2
59324945-EC44-4C0D-B1CD-9DB139DF070C: Attempt 3
59324945-EC44-4C0D-B1CD-9DB139DF070C: Attempt 4
59324945-EC44-4C0D-B1CD-9DB139DF070C: Attempt 5
59324945-EC44-4C0D-B1CD-9DB139DF070C: Attempt 6
59324945-EC44-4C0D-B1CD-9DB139DF070C: Attempt 7
4B47D616-A8D6-4552-9D44-CCAD2E0F4CF9: InitialAttemptOrder
59324945-EC44-4C0D-B1CD-9DB139DF070C: Attempt 8
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: Boot0000
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: Timeout
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: PlatformLang
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: Lang
04B37FE8-F6AE-480B-BDD5-37D98C5E89AA: VarErrorFlag
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: Key0000
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: Key0001
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: Boot0001
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: Boot0002
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: Boot0003
4C19049F-4137-4DD3-9C10-8B97A83FFDFA: MemoryTypeInformation
5B446ED1-E30B-4FAA-871A-3654ECA36080: 525400123456
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: BootOrder
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: Boot0004
EB704011-1402-11D3-8E77-00A0C969723B: MTC
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: ConOut
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: ConIn
8BE4DF61-93CA-11D2-AA0D-00E098032B8C: ErrOut
```

`8BE4DF61-93CA-11D2-AA0D-00E098032B8C`를 GUID로 가지고 있는 그룹이 제일 중요하다.

`EFI_GLOBAL_VARIABLE`을 뜻하는 GUID며 UEFI 스펙에 정의되어 있다.

EDKII에서는 여기에서 찾을 수 있다.

{% embed url="<https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Guid/GlobalVariable.h>" %}

```c
#define EFI_GLOBAL_VARIABLE \
  { \
    0x8BE4DF61, 0x93CA, 0x11d2, {0xAA, 0x0D, 0x00, 0xE0, 0x98, 0x03, 0x2B, 0x8C } \
  }

extern EFI_GUID gEfiGlobalVariableGuid;
```

`Boot####`같은 옵션들은 UEFI 스펙에서 정의되므로 미리 정의된 GUID인 `EFI_GLOBAL_VARIABLE`를 가지고 있다. 고유한 옵션을 만들고 싶다면 EFI\_GLOBAL\_VARIABLE을 사용하면 안되고 충돌 가능성을 없애기 위해 고유한 옵션을 만들어야한다.

EDKII 코드베이스에서 GUID가 정의된 위치를 보려면 다음과 같이 하면 된다.

```shell
$ grep -i 4B37FE8 -r ./ --exclude-dir=Build
```

GUID별로 변수를 정렬하려면 위의 명령 실행결과를 파일로 저장하고 Linux Shell에서 정렬을 수행하면 된다.

```shell
$ cat guids.txt | sort
```

여기서부터는 GUID에 대한 정의가 있는 파일이 있고 그룹화된 GUID를 쓰는 변수들의 목록이다.

`8BE4DF61-93CA-11D2-AA0D-00E098032B8C` - `gEfiGlobalVariableGuid`

{% embed url="<https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Guid/GlobalVariable.h>" %}

{% embed url="<https://github.com/tianocore/edk2/blob/master/MdePkg/MdePkg.dec>" %}

```
Boot0000
Boot0001
Boot0002
Boot0003
Boot0004
BootCurrent
BootOptionSupport
BootOrder
ConIn
ConInDev
ConOut
ConOutDev
ErrOut
ErrOutDev
Key0000
Key0001
Lang
LangCodes
OsIndicationsSupported
PlatformLang
PlatformLangCodes
PlatformRecovery0000
Timeout
```

`04B37FE8-F6AE-480B-BDD5-37D98C5E89AA` - `gEdkiiVarErrorFlagGuid`

<https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Include/Guid/VarErrorFlag.h>

<https://github.com/tianocore/edk2/blob/master/MdeModulePkg/MdeModulePkg.dec>

```
VarErrorFlag
```

`4C19049F-4137-4DD3-9C10-8B97A83FFDFA` - `gEfiMemoryTypeInformationGuid`

<https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Include/Guid/MemoryTypeInformation.h>

<https://github.com/tianocore/edk2/blob/master/MdeModulePkg/MdeModulePkg.dec>

```
MemoryTypeInformation
```

`5B446ED1-E30B-4FAA-871A-3654ECA36080` - `gEfiIp4Config2ProtocolGuid`

<https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Protocol/Ip4Config2.h>

<https://github.com/tianocore/edk2/blob/master/MdePkg/MdePkg.dec>

```
525400123456
```

`EB704011-1402-11D3-8E77-00A0C969723B` - `gMtcVendorGuid`

<https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Include/Guid/MtcVendor.h>

<https://github.com/tianocore/edk2/blob/master/MdeModulePkg/MdeModulePkg.dec>

```
MTC
```

`59324945-EC44-4C0D-B1CD-9DB139DF070C` - `gEfiIScsiInitiatorNameProtocolGuid`

<https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Protocol/IScsiInitiatorName.h>

<https://github.com/tianocore/edk2/blob/master/MdePkg/MdePkg.dec>

```
Attempt 1
Attempt 2
Attempt 3
Attempt 4
Attempt 5
Attempt 6
Attempt 7
Attempt 8
```

`158DEF5A-F656-419C-B027-7A3192C079D2` - `gShellVariableGuid`

<https://github.com/tianocore/edk2/blob/master/ShellPkg/Include/Guid/ShellVariableGuid.h>

<https://github.com/tianocore/edk2/blob/master/ShellPkg/ShellPkg.dec>

```
cwd
debuglasterror
lasterror
nonesting
path
profiles
uefishellsupport
uefishellversion
uefiversion
```

`4B47D616-A8D6-4552-9D44-CCAD2E0F4CF9` - `gIScsiConfigGuid`

<https://github.com/tianocore/edk2/blob/master/NetworkPkg/Include/Guid/IScsiConfigHii.h>

<https://github.com/tianocore/edk2/blob/master/NetworkPkg/NetworkPkg.dec>

```
InitialAttemptOrder
```

`0053D9D6-2659-4599-A26B-EF4536E631A9` - `gShellAliasGuid`

<https://github.com/tianocore/edk2/blob/master/ShellPkg/Include/Guid/ShellAliasGuid.h>

<https://github.com/tianocore/edk2/blob/master/ShellPkg/ShellPkg.dec>

```
cat
cd..
cd\
copy
del
dir
md
mem
mount
move
ren
```


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