EFI FIRMWARE VOLUME PROTOCOL

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The Firmware Volume Protocol provides file-level access to the firmware volume. Each firmware volume driver must produce an instance of the Firmware Volume Protocol if the firmware volume is to be visible to the system. The Firmware Volume Protocol also provides mechanisms for determining and modifying some attributes of the firmware volume.

Contents

GUID

#include EFI_PROTOCOL_CONSUMER(FirmwareVolume)
extern EFI_GUID gEfiFirmwareVolumeGuid;

#define EFI_FIRMWARE_VOLUME_PROTOCOL_GUID \
  { 0x389F751F, 0x1838, 0x4388, 0x83, 0x90, 0xCD, 0x81, 0x54, 0xBD, 0x27, 0xF8 }

Protocol Interface Structure

typedef struct {
  EFI_FV_GET_ATTRIBUTES GetVolumeAttributes;
  EFI_FV_SET_ATTRIBUTES SetVolumeAttributes;
  EFI_FV_READ_FILE      ReadFile;
  EFI_FV_READ_SECTION   ReadSection;
  EFI_FV_WRITE_FILE     WriteFile;
  EFI_FV_GET_NEXT_FILE  GetNextFile;
  UINT32                KeySize;
  EFI_HANDLE            ParentHandle;
} EFI_FIRMWARE_VOLUME_PROTOCOL;

Members

Member Description
GetVolumeAttributes Retrieves volume capabilities and current settings.
SetVolumeAttributes Modifies the current settings of the firmware volume.
ReadFile Reads an entire file from the firmware volume.
ReadSection Reads a single section from a file into a buffer.
WriteFile Writes an entire file into the firmware volume.
GetNextFile Provides service to allow searching the firmware volume.
KeySize Data field that indicates the size in bytes of the Key input buffer for the
ParentHandle Handle of the parent firmware volume.

Description

The Firmware Volume Protocol contains the file-level abstraction to the firmware volume as well as some firmware volume attribute reporting and configuration services. The Firmware Volume Protocol is the interface used by all parts of DXE that are not directly involved with managing the firmware volume itself.T his abstraction allows many varied types of firmware volume implementations.A firmware volume may be a flash device or it may be a file in the EFI system partition, for example. This level of firmware volume implementation detail is not visible to the consumers of the Firmware Volume Protocol.

GetVolumeAttributes()

Returns the attributes and current settings of the firmware volume.

Prototype

EFI_STATUS
(EFIAPI * EFI_FV_GET_ATTRIBUTES) (
  IN  EFI_FIRMWARE_VOLUME_PROTOCOL *This,
  OUT EFI_FV_ATTRIBUTES            *FvAttributes
  );

Parameters

Parameter Description
This Indicates the EFI_FIRMWARE_VOLUME_PROTOCOL instance.
FvAttributes Pointer to an EFI_FV_ATTRIBUTES in which the attributes and current settings are returned.

Description
Because of constraints imposed by the underlying firmware storage, an instance of the Firmware Volume Protocol may not be to able to support all possible variations of this architecture. These constraints and the current state of the firmware volume are exposed to the caller using the GetVolumeAttributes() function.

GetVolumeAttributes() is callable only from EFI_TPL_NOTIFY and below. Behavior of GetVolumeAttributes() at any EFI_TPL above EFI_TPL_NOTIFY is undefined.

Status Codes Returned

Status Code Description
EFI_SUCCESS The firmware volume attributes were returned.

SetVolumeAttributes()

Modifies the current settings of the firmware volume according to the input parameter.

Prototype

EFI_STATUS
(EFIAPI * EFI_FV_SET_ATTRIBUTES) (
  IN     EFI_FIRMWARE_VOLUME_PROTOCOL *This,
  IN OUT EFI_FV_ATTRIBUTES            *FvAttributes
  );

Parameters

Parameter Description
This Indicates the EFI_FIRMWARE_VOLUME_PROTOCOL instance.
FvAttributes On input, FvAttributes is a pointer to an EFI_FV_ATTRIBUTES containing the desired firmware volume settings. On successful return, it contains the new settings of the firmware volume. On unsuccessful return, FvAttributes is not modified and the firmware volume settings are not changed.

Description
The SetVolumeAttributes() function is used to set configurable firmware volume attributes.O nly EFI_FV_READ_STATUS, EFI_FV_WRITE_STATUS, and EFI_FV_LOCK_STATUS may be modified, and then only in accordance with the declared capabilities.A ll other bits of *FvAttributes are ignored on input.On successful return, all bits of *FvAttributes are valid and it contains the completed EFI_FV_ATTRIBUTES for the volume.

To modify an attribute, the corresponding status bit in the EFI_FV_ATTRIBUTES is set to the desired value on input. The EFI_FV_LOCK_STATUS bit does not affect the ability to read or write the firmware volume.R ather, once the EFI_FV_LOCK_STATUS bit is set, it prevents further modification to all the attribute bits.

SetVolumeAttributes() is callable only from EFI_TPL_NOTIFY and below. Behavior of SetVolumeAttributes() at any EFI_TPL above EFI_TPL_NOTIFY is undefined.

Status Codes Returned

Status Code Description
EFI_SUCCESS The requested firmware volume attributes were set and the resulting EFI_FV_ATTRIBUTES is returned in FvAttributes.
EFI_INVALID_PARAMETER FvAttributes:EFI_FV_READ_STATUS is set to 1 on input, but the device does not support enabling reads. (FvAttributes:EFI_FV_READ_ENABLE_CAP is clear on return from GetVolumeAttributes()). Actual volume attributes are unchanged.
EFI_INVALID_PARAMETER FvAttributes:EFI_FV_READ_STATUS is cleared to 0 on input, but the device does not support disabling reads (FvAttributes:EFI_FV_READ_DISABLE_CAP is clear on return from GetVolumeAttributes()). Actual volume attributes are unchanged.
EFI_INVALID_PARAMETER FvAttributes:EFI_FV_WRITE_STATUS is set to 1 on input, but the device does not support enabling writes (FvAttributes:EFI_FV_WRITE_ENABLE_CAP is clear on return from GetVolumeAttributes()). Actual volume attributes are unchanged.
EFI_INVALID_PARAMETER FvAttributes:EFI_FV_WRITE_STATUS is cleared to 0 on input, but the device does not support disabling writes (FvAttributes:EFI_FV_WRITE_DISABLE_CAP is clear on return from GetVolumeAttributes()). Actual volume attributes are unchanged.
EFI_INVALID_PARAMETER FvAttributes:EFI_FV_LOCK_STATUS is set on input, but the device does not support locking (FvAttributes:EFI_FV_LOCK_CAP is clear on return from GetVolumeAttributes()). Actual volume attributes are unchanged.
EFI_ACCESS_DENIED Device is locked and does not allow attribute modification (FvAttributes:EFI_FV_LOCK_STATUS is set on return from GetVolumeAttributes()). Actual volume attributes are unchanged.

ReadFile()

Retrieves a file and/or file information from the firmware volume.

Prototype

EFI_STATUS
(EFIAPI * EFI_FV_READ_FILE) (
  IN     EFI_FIRMWARE_VOLUME_PROTOCOL *This,
  IN     EFI_GUID                     *NameGuid,
  IN OUT VOID                         **Buffer,
  IN OUT UINTN                        *BufferSize,
  OUT    EFI_FV_FILETYPE              *FoundType,
  OUT    EFI_FV_FILE_ATTRIBUTES       *FileAttributes,
  OUT    UINT32                       *AuthenticationStatus
  );

Parameters

Parameter Description
This Indicates the EFI_FIRMWARE_VOLUME_PROTOCOL instance.
NameGuid A pointer to an EFI_GUID that specifies the file name. All firmware file names are EFI_GUIDs. A single firmware volume must not have two valid files with the same file name EFI_GUID.
Buffer Pointer to a pointer to a buffer in which the file or section contents are returned.
BufferSize Pointer to a caller-allocated UINTN. It indicates the size of the memory represented by *Buffer.
FoundType Pointer to a caller-allocated EFI_FV_FILETYPE.
FileAttributes Pointer to a caller-allocated EFI_FV_FILE_ATTRIBUTES.
AuthenticationStatus Pointer to a caller-allocated UINT32 in which the authentication status is returned.

Description
ReadFile() is used to retrieve any file from a firmware volume during the DXE phase. The actual binary encoding of the file in the firmware volume media may be in any arbitrary format as long as it does the following:

  • It is accessed using the Firmware Volume Protocol.
  • The image that is returned follows the Tiano image format.

If the input value of Buffer==NULL, it indicates the caller is requesting only that the type, attributes, and size of the file be returned and that there is no output buffer. In this case, the following occurs:

  • *BufferSize is returned with the size that is required to successfully complete the read.
  • The output parameters *FoundType and *FileAttributes are returned with valid values.
  • The returned value of *AuthenticationStatus is undefined.

If the input value of Buffer!=NULL, the output buffer is specified by a double indirection of the Buffer parameter. The input value of *Buffer is used to determine if the output buffer is caller allocated or is dynamically allocated by ReadFile().

If the input value of *Buffer!=NULL, it indicates the output buffer is caller allocated. In this case, the input value of *BufferSize indicates the size of the caller-allocated output buffer. If the output buffer is not large enough to contain the entire requested output, it is filled up to the point that the output buffer is exhausted and EFI_WARN_BUFFER_TOO_SMALL is returned, and then *BufferSize is returned with the size required to successfully complete the read. All other output parameters are returned with valid values.

If the input value of *Buffer==NULL, it indicates the output buffer is to be allocated by ReadFile(). In this case, ReadFile() will allocate an appropriately sized buffer from boot services pool memory, which will be returned in *Buffer. The size of the new buffer is returned in *BufferSize and all other output parameters are returned with valid values.

ReadFile() is callable only from EFI_TPL_NOTIFY and below. Behavior of ReadFile() at any EFI_TPL above EFI_TPL_NOTIFY is undefined.


Status Codes Returned

Status Code Description
EFI_SUCCESS The call completed successfully.
EFI_WARN_BUFFER_TOO_SMALL The buffer is too small to contain the requested output. The buffer is filled and the output is truncated.
EFI_OUT_OF_RESOURCES An allocation failure occurred.
EFI_NOT_FOUND Name was not found in the firmware volume.
EFI_DEVICE_ERROR A hardware error occurred when attempting to access the firmware volume.
EFI_ACCESS_DENIED The firmware volume is configured to disallow reads.

ReadSection()

Locates the requested section within a file and returns it in a buffer.

Prototype

typedef 
EFI_STATUS
(EFIAPI * EFI_FV_READ_SECTION) (
  IN     EFI_FIRMWARE_VOLUME_PROTOCOL *This,
  IN     EFI_GUID                     *NameGuid,
  IN     EFI_SECTION_TYPE             SectionType,
  IN     UINTN                        SectionInstance,
  IN OUT VOID                         **Buffer,
  IN OUT UINTN                        *BufferSize,
  OUT    UINT32                       *AuthenticationStatus
  );

Parameters

Parameter Description
This A poonter to this instance of the the EFI_FIRMWARE_VOLUME_PROTOCOL instance.
NameGuid A pointer to an EFI_GUID that specifies the file name from which the requested section will be read.
SectionType Indicates the section type to return. SectionType in conjunction with SectionInstance indicates which section to return.
SectionInstance An unsigned integer that specifies the zero-based instance of the sections with a type of SectionType to return. SectionType in conjunction with SectionInstance indicates which section to return.
Buffer A ponter to a pointer to a buffer in which the file or section contents are returned, not including the section header.
BufferSize A pointer to to a caller-allocated UINTN. It indicates the size of the memory represented by *Buffer.
AuthenticationStatus A pointer to a caller-allocated UINT32 in which the authentication status is returned.

Description
ReadSection() is used to retrieve a specific section from a file within a firmware volume. The section returned is determined using a depth-first, left-to-right search algorithm through all sections found in the specified file.

The output buffer is specified by a double indirection of the Buffer parameter. The input value of *Buffer is used to determine if the output buffer is caller allocated or is dynamically allocated by ReadSection().

If the input value of *Buffer!=NULL, it indicates that the output buffer is caller allocated. In this case, the input value of *BufferSize indicates the size of the caller-allocated output buffer.

If the output buffer is not large enough to contain the entire requested output, it is filled up to the point that the output buffer is exhausted and EFI_WARN_BUFFER_TOO_SMALL is returned, and then *BufferSize is returned with the size that is required to successfully complete the read.

All other output parameters are returned with valid values.

If the input value of *Buffer==NULL, it indicates the output buffer is to be allocated by ReadSection(). In this case, ReadSection() will allocate an appropriately sized buffer from boot services pool memory, which will be returned in *Buffer. The size of the new buffer is returned in *BufferSize and all other output parameters are returned with valid values.

ReadSection() is callable only from EFI_TPL_NOTIFY and below. Behavior of ReadSection() at any EFI_TPL above EFI_TPL_NOTIFY is undefined.

Status Codes Returned

Status Code Description
EFI_SUCCESS The call completed successfully.
EFI_WARN_BUFFER_TOO_SMALL The caller-allocated buffer is too small to contain the requested output. The buffer is filled and the output is truncated.
EFI_OUT_OF_RESOURCES An allocation failure occurred.
EFI_NOT_FOUND The requested file was not found in the firmware volume.
EFI_NOT_FOUND The requested section was not found in the specified file.
EFI_DEVICE_ERROR A hardware error occurred when attempting to access the firmware volume.
EFI_ACCESS_DENIED The firmware volume is configured to disallow reads.
EFI_PROTOCOL_ERROR The requested section was not found, but the file could not be fully parsed because a required EFI_GUIDED_SECTION_EXTRACTION_PROTOCOL was not found. It is possible the requested section exists within the file and could be successfully extracted once the required EFI_GUIDED_SECTION_EXTRACTION_PROTOCOL is published.

WriteFile()

Writes one or more files to the firmware volume.

Prototype

typedef 
EFI_STATUS
(EFIAPI * EFI_FV_WRITE_FILE) (
  IN EFI_FIRMWARE_VOLUME_PROTOCOL *This,
  IN UINT32                       NumberOfFiles,
  IN EFI_FV_WRITE_POLICY          WritePolicy,
  IN EFI_FV_WRITE_FILE_DATA       *FileData
  );

Parameters

Parameter Description
This Indicates the EFI_FIRMWARE_VOLUME_PROTOCOL instance.
NumberOfFiles Indicates the number of elements in the array pointed to by FileData.
WritePolicy Indicates the level of reliability for the write in the event of a power failure or other system failure during the write operation.
FileData Pointer to an array of EFI_FV_WRITE_FILE_DATA. Each element of FileData[] represents a file to be written.

Description
WriteFile() is used to write one or more files to a firmware volume.E ach file to be written is described by an EFI_FV_WRITE_FILE_DATA structure.

The caller must ensure that any required alignment for all files listed in the FileData array is compatible with the firmware volume. Firmware volume capabilities can be determined using the GetVolumeAttributes() call.

Similarly, if the WritePolicy is set to EFI_FV_RELIABLE_WRITE, the caller must check the firmware volume capabilities to ensure EFI_FV_RELIABLE_WRITE is supported by the firmware volume. EFI_FV_UNRELIABLE_WRITE must always be supported.

Writing a file with a size of zero (FileData[n].BufferSize == 0) deletes the file from the firmware volume if it exists. Deleting a file must be done one at a time. Deleting a file as part of a multiple file write is not allowed.

WriteFile() is callable only from EFI_TPL_NOTIFY and below. Behavior of WriteFile() at any EFI_TPL above EFI_TPL_NOTIFY is undefined.

Other than EFI_DEVICE_ERROR, all error codes imply the firmware volume has not been modified. In the case of EFI_DEVICE_ERROR, the firmware volume may have been corrupted and appropriate repair steps must be taken.

Status Codes Returned

Status Code Description
EFI_SUCCESS The write completed successfully.
EFI_OUT_OF_RESOURCES The firmware volume does not have enough free space to store file(s).
EFI_DEVICE_ERROR A hardware error occurred when attempting to access the firmware volume.
EFI_WRITE_PROTECTED The firmware volume is configured to disallow writes.
EFI_NOT_FOUND A delete was requested, but the requested file was not found in the firmware volume.
EFI_INVALID_PARAMETER A delete was requested with a multiple file write.
EFI_INVALID_PARAMETER An unsupported WritePolicy was requested.
EFI_INVALID_PARAMETER An unknown file type was specified.
EFI_INVALID_PARAMETER A file system specific error has occurred.

GetNextFile()

Retrieves information about the next file in the firmware volume store that matches the search criteria.

Prototype

EFI_STATUS
(EFIAPI *EFI_FV_GET_NEXT_FILE) (
  IN     EFI_FIRMWARE_VOLUME_PROTOCOL *This,
  IN OUT VOID                         *Key,
  IN OUT EFI_FV_FILETYPE              *FileType,
  OUT    EFI_GUID                     *NameGuid,
  OUT    EFI_FV_FILE_ATTRIBUTES       *Attributes,
  OUT    UINTN                        *Size
  );

Parameters

Parameter Description
This Indicates the EFI_FIRMWARE_VOLUME_PROTOCOL instance.
Key Pointer to a caller-allocated buffer that contains implementation-specific data that is used to track where to begin the search for the next file. The size of the buffer must be at least This->KeySize bytes long.To reinitialize the search and begin from the beginning of the firmware volume, the entire buffer must be cleared to zero. Other than clearing the buffer to initiate a new search, the caller must not modify the data in the buffer between calls to GetNextFile().
FileType Pointer to a caller-allocated EFI_FV_FILETYPE. The GetNextFile() API can filter its search for files based on the value of the *FileType input. A *FileType input of EFI_FV_FILETYPE_ALL causes GetNextFile() to search for files of all types.If a file is found, the file’s type is returned in *FileType. *FileType is not modified if no file is found.
NameGuid Pointer to a caller-allocated EFI_GUID.If a matching file is found, the file’s name is returned in*NameGuid. If no matching file is found, *NameGuid is not modified.
Attributes Pointer to a caller-allocated EFI_FV_FILE_ATTRIBUTES. If a matching file is found, the file’s attributes are returned in *Attributes. If no matching file is found, *Attributes is not modified.
Size Pointer to a caller-allocated UINTN.If a matching file is found, the file’s size is returned in *Size.If no matching file is found, *Size is not modified.

Description
GetNextFile() is the interface that is used to search a firmware volume for a particular file. It is called successively until the desired file is located or the function returns EFI_NOT_FOUND.

To filter uninteresting files from the output, the type of file to search for may be specified in *FileType. For example, if *FileType is EFI_FV_FILETYPE_DRIVER, only files of this type will be returned in the output. If *FileType is EFI_FV_FILETYPE_ALL, no filtering of file types is done.

The Key parameter is used to indicate a starting point of the search.If the buffer *Key is completely initialized to zero, the search reinitialized and starts at the beginning. Subsequent calls to GetNextFile() must maintain the value of *Key returned by the immediately previous call.

The actual contents of *Key are implementation specific and no semantic content is implied.

GetNextFile() is callable only from EFI_TPL_NOTIFY and below. Behavior of GetNextFile() at any EFI_TPL above EFI_TPL_NOTIFY is undefined.

Status Codes Returned

Status Code Description
EFI_SUCCESS The output parameters are filled with data obtained from the first matching file that was found.
EFI_NOT_FOUND No files of type FileType were found.
EFI_DEVICE_ERROR A hardware error occurred when attempting to access the firmware volume.
EFI_ACCESS_DENIED The firmware volume is configured to disallow reads.

Copyright (C) 2008 Phoenix Technologies Ltd. All Rights Reserved. Portions (C) 1999-2003 Intel Corporation. Used with permission.

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