12.3.3 HII Config Access Protocol

The HII Config Access Protocol is produced by the UEFI driver. It has three key functions that are published to the HII database. The first two functions are used by the Configuration Routing Protocol to extract data from drivers and to provide configuration back to the drivers. The format of the configuration is modeled after the CGI: A Unicode string of ampersand separated name = value pairs (x=1&y=2&z=3A). The names and values are specified in the forms. Only names are provided for extract requests. The driver cannot assume that all names in a form are present in a request―the caller may limit the entries to only those it needs.

Callbacks are the method by which the browser and driver directly communicate with each other. The forms describe when to invoke callbacks and they provide some context for the callback.

Use callbacks to update dynamic data, such as ambient temperature, fan speed, etc. They should not be used to modify how items are displayed.

The following three key functions are published to the HII database:

  • ExtractConfig function: This function is called by the HII engine at the

    beginning of a particular form. This function gives the driver a chance to

    perform tasks before the form is processed by the HII database engine. For

    example, the function could test the current NVRAM data structure to make

    sure it is not corrupt. This function also allows the browser to display

    current configuration information.

Note: The ExtractConfig function eliminates the need to use the previous, tedious method of manually outputting to the console, reading strings back from the console, and manually interpreting those strings.

  • RouteConfig function: This function allows the browser to obtain and change configuration information upon the exit of the form. It performs the final store and routes the appropriate data out to whoever needs it. For example, this function copies the current data back to the data structure in NVRAM. This function processes any changes that the user enters.

  • Callback function: This function is called when a user makes changes. After the changes are saved, the original data structure is updated with the new settings.

Note: This is not a callback in the traditional sense. This function is used by the browser to route data back to the appropriate driver so each driver can process its own configuration.

12.3.3.1 Sample code for routing protocols

The following three examples show how the ExtractConfig, RouteConfig, and Callback functions of the Config Access Protocol may be used.

Example 139-ExtractConfig() Function

EFI_STATUS
EFIAPI
ExtractConfig (
IN CONST EFI_HII_CONFIG_ACCESS_PROTOCOL *This,
IN CONST EFI_STRING Request,
OUT EFI_STRING *Progress,
OUT EFI_STRING *Results
)
{
EFI_STATUS Status;
UINTN BufferSize;
DRIVER_SAMPLE_PRIVATE_DATA *PrivateData;
EFI_HII_CONFIG_ROUTING_PROTOCOL *HiiConfigRouting;
EFI_STRING ConfigRequest;
EFI_STRING ConfigRequestHdr;
UINTN Size;
BOOLEAN AllocatedRequest;
if (Progress == NULL || Results == NULL) {
return EFI_INVALID_PARAMETER;
}
// Initialize the local variables.
ConfigRequestHdr = NULL;
ConfigRequest = NULL;
Size = 0;
*Progress = Request;
AllocatedRequest = FALSE;
PrivateData = DRIVER_SAMPLE_PRIVATE_FROM_THIS (This);
HiiConfigRouting = PrivateData->HiiConfigRouting;
// Get Buffer Storage data from EFI variable.
// Try to get the current setting from variable.
BufferSize = sizeof (DRIVER_SAMPLE_CONFIGURATION);
Status = gRT->GetVariable (
VariableName,
&mFormSetGuid,
NULL,
&BufferSize,
&PrivateData->Configuration
);
if (EFI_ERROR (Status)) {
return EFI_NOT_FOUND;
}
if (Request == NULL) {
// Request is set to NULL, construct full request string.
//
// Allocate and fill a buffer large enough to hold the <ConfigHdr> template
// followed by "&OFFSET=0&WIDTH=WWWWWWWWWWWWWWWW" followed by a Null-terminator
ConfigRequestHdr = HiiConstructConfigHdr (
&mFormSetGuid,
VariableName,
PrivateData->DriverHandle[0]
);
Size = (StrLen (ConfigRequestHdr) + 32 + 1) * sizeof (CHAR16);
ConfigRequest = AllocateZeroPool (Size);
ASSERT (ConfigRequest != NULL);
AllocatedRequest = TRUE;
UnicodeSPrint (
ConfigRequest,
Size,
L"%s&OFFSET=0&WIDTH=%016LX",
ConfigRequestHdr,
(UINT64)BufferSize
);
FreePool (ConfigRequestHdr);
} else {
// Check routing data in <ConfigHdr>.
// Note: if only one Storage is used, then this checking could be skipped.
if (!HiiIsConfigHdrMatch (Request, &mFormSetGuid, NULL)) {
return EFI_NOT_FOUND;
}
// Set Request to the unified request string.
ConfigRequest = Request;
// Convert buffer data to <ConfigResp> by helper function BlockToConfig()
Status = HiiConfigRouting->BlockToConfig (
HiiConfigRouting,
ConfigRequest,
(UINT8 *) &PrivateData->Configuration,
BufferSize,
Results, Progress
);
}
// Free the allocated config request string.
if (AllocatedRequest) {
FreePool (ConfigRequest);
// Set Progress string to the original request string.
if (Request == NULL) {
*Progress = NULL;
} else if (StrStr (Request, L"OFFSET") == NULL) {
*Progress = Request + StrLen (Request);
}
return Status;
}
. .
return EFI_SUCESS
}

Example 140-RouteConfig() Function

EFI_STATUS
EFIAPI
RouteConfig (
IN CONST EFI_HII_CONFIG_ACCESS_PROTOCOL *This,
IN CONST EFI_STRING Configuration,
OUT EFI_STRING *Progress
)
{
EFI_STATUS Status;
UINTN BufferSize;
DRIVER_SAMPLE_PRIVATE_DATA *PrivateData;
EFI_HII_CONFIG_ROUTING_PROTOCOL *HiiConfigRouting;
. .
if (Configuration == NULL || Progress == NULL) {
return EFI_INVALID_PARAMETER;
}
PrivateData = DRIVER_SAMPLE_PRIVATE_FROM_THIS (This);
HiiConfigRouting = PrivateData->HiiConfigRouting;
*Progress = Configuration;
// Check routing data in <ConfigHdr>.
// Note: if only one Storage is used, then this checking could be
// skipped. if (!HiiIsConfigHdrMatch (Configuration, &mFormSetGuid, NULL)) { return EFI_NOT_FOUND;
}
//
// Get Buffer Storage data from EFI variable
//
BufferSize = sizeof (DRIVER_SAMPLE_CONFIGURATION);
Status = gRT->GetVariable (
VariableName,
&mFormSetGuid,
NULL,
&BufferSize,
&PrivateData->Configuration
);
if (EFI_ERROR (Status)) {
return Status;
}
// Convert <ConfigResp> to buffer data by helper function ConfigToBlock() BufferSize = sizeof (DRIVER_SAMPLE_CONFIGURATION);
Status = HiiConfigRouting->ConfigToBlock (
HiiConfigRouting,
Configuration,
(UINT8 *) &PrivateData->Configuration,
&BufferSize,
Progress
);
if (EFI_ERROR (Status)) {
return Status;
}
// Store Buffer Storage back to EFI variable
Status = gRT->SetVariable (
VariableName,
&mFormSetGuid,
EFI_VARIABLE_NON_VOLATILE | EFI_VARIABLE_BOOTSERVICE_ACCESS,
sizeof (DRIVER_SAMPLE_CONFIGURATION),
&PrivateData->Configuration
);
return Status;
}

Example 141-Callback function

EFI_STATUS
EFIAPI
DriverCallback (
IN CONST EFI_HII_CONFIG_ACCESS_PROTOCOL *This,
IN EFI_BROWSER_ACTION Action,
IN EFI_QUESTION_ID QuestionId,
IN UINT8 Type,
IN EFI_IFR_TYPE_VALUE *Value,
OUT EFI_BROWSER_ACTION_REQUEST *ActionRequest
)
{
DRIVER_SAMPLE_PRIVATE_DATA *PrivateData;
EFI_STATUS Status;
if ((Value == NULL) || (ActionRequest == NULL)) {
return EFI_INVALID_PARAMETER;
}
Status = EFI_SUCCESS;
PrivateData = DRIVER_SAMPLE_PRIVATE_FROM_THIS (This);
switch (QuestionId) {
case 0x1234: // do some code break;
default:
break;
}
return Status;
}