5.3.8 GetNextVariableName()

This service is used to traverse the list of UEFI variables that are maintained through the UEFI Variable Services. Since, in general, UEFI drivers know the specific UEFI variables that the UEFI Driver is required to access, there is no need for a UEFI driver to traverse the list of all the UEFI variables. This service is typically used by UEFI applications, such as a diagnostic or a debug utility, to show the contents of all the UEFI Variables present in a platform.

The example below shows how the GetNextVariableName() service can be used to traverse and print the entire contents of the UEFI variable store. It uses the EDK II MemoryAllocationLib to allocate, reallocate, and free buffers; the EDK II UefiLib to print formatted strings to the UEFI console output device; and the EDK II UefiRuntimeServicesTableLib to call the GetNextVariableName() and GetVariable() runtime services.

Example 83-Print all UEFI variable store contents

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

EFI_STATUS Status;
EFI_GUID Guid;
UINTN NameBufferSize;
UINTN NameSize;
CHAR16 *Name;
UINTN DataSize;
UINT8 *Data;
UINTN Index;

//
// Initialize the variable name and data buffer variables
// to retrieve the first variable name in the variable store
//
NameBufferSize = sizeof (CHAR16);
Name = AllocateZeroPool (NameBufferSize);

//
// Loop through all variables in the variable store
//
while (TRUE) {
  //
  // Loop until a large a large enough variable name buffer is allocated
  // do {
  NameSize = NameBufferSize;
  Status = gRT->GetNextVariableName (&NameSize, Name, &Guid);
  if (Status == EFI_BUFFER_TOO_SMALL) {
    //
    // Grow the buffer Name to NameSize bytes
    //
    Name = ReallocatePool (NameBufferSize, NameSize, Name);
    if (Name == NULL) {
      return EFI_OUT_OF_RESOURCES;
    }
    NameBufferSize = NameSize;
  }
}
while (Status == EFI_BUFFER_TOO_SMALL);

//
// Exit main loop after last variable name is retrieved
//
if (EFI_ERROR (Status)) {
  FreePool (Name);
  return Status;
}

//
// Print variable guid and name
//
Print (L"%g : %s", &Guid, Name);

//
// Initialize variable data buffer as an empty buffer
//
DataSize = 0;
Data = NULL;

//
// Loop until a large enough variable data buffer is allocated
//
do {
  Status = gRT->GetVariable (Name, &Guid, NULL, &DataSize, Data);
  if (Status == EFI_BUFFER_TOO_SMALL) {
    //
    // Allocate new buffer for the variable data
    //
    Data = AllocatePool (DataSize);
    if (Data == NULL) {
      FreePool (Name);
      return EFI_OUT_OF_RESOURCES;
    }
  }
} while (Status == EFI_BUFFER_TOO_SMALL);
if (EFI_ERROR (Status)) {
  FreePool (Data);
  FreePool (Name);
  return Status;
}

//
// Print variable data
//
for (Index = 0; Index < DataSize; Index++) {
  if ((Index & 0x0f) == 0) {
    Print (L"\n ");
  }
  Print (L"%02x ", Data[Index]);
}
Print (L"\n");
FreePool (Data);
}