SetupDesignGuide.pdf - Firmware Encoding Index

Setup Design Guide
DRAFT
7.3.1 EFI_FORM_CALLBACK_PROTOCOL.NvRead()
Summary
Returns the value of a variable.
Prototype
EFI_STATUS
(EFIAPI *EFI_NV_READ) (
IN EFI_FORM_CALLBACK_PROTOCOL *This,
IN CHAR16
*VariableName,
IN EFI_GUID
*VendorGuid,
OUT UINT32
*Attributes OPTIONAL,
IN OUT UINTN
*DataSize,
OUT VOID
*Buffer
);
Parameters
This
VariableName
VendorGuid
Attributes
DataSize
Buffer
A pointer to the EFI_FORM_CALLBACK_PROTOCOL instance.
A Null-terminated Unicode string that is the name of the vendor’s
variable.
A unique identifier for the vendor.
If not NULL, a pointer to the memory location to return the attributes
bit-mask for the variable. See “Related Definitions”.
The size in bytes of the Buffer. A size of zero causes the variable
to be deleted.
The buffer to return the contents of the variable.
Related Definitions
//*********************************************************
// Variable Attributes
//*********************************************************
#define EFI_VARIABLE_NON_VOLATILE
0x0000000000000001
#define EFI_VARIABLE_BOOTSERVICE_ACCESS 0x0000000000000002
#define EFI_VARIABLE_RUNTIME_ACCESS
0x0000000000000004
Description
Each vendor may create and manage its own variables with the risk of name conflicts by using a unique
VendorGuid. When a variable is set its Attributes are supplied to indicate how the data variable
should be stored and maintained by the system. Any attempts to access a variable that does not have
the attribute set for runtime access will yield the EFI_NOT_FOUND error.
Status Codes Returned
73