MAN page from OpenSuSE efivar-devel-37-lp152.3.12.1.i586.rpm


Section: C Library Functions (3)
Updated: Thu Nov 11 2014


efi_variable_import, efi_variable_export, efi_variable_alloc,efi_variable_free, efi_variable_set_name, efi_variable_get_name,efi_variable_set_guid, efi_variable_get_guid,efi_variable_set_data, efi_variable_get_data,efi_variable_set_attributes, efi_variable_get_attributes,efi_variable_realize - utility functions to import and export UEFI variables to files. 


#include <efivar.h>typedef struct efi_variable efi_variable_t;ssize_t efi_variable_import(uint8_t *data, size_t size, efi_variable_t **var);ssize_t efi_variable_export(efi_variable_t *var, uint8_t **data, size_t *size);efi_variable_t *efi_variable_alloc(void);void efi_variable_free(efi_variable_t *var, int free_data);int efi_variable_set_name(efi_variable_t *var, char *name);char *efi_variable_get_name(efi_variable_t *var);int efi_variable_set_guid(efi_variable_t *var, efi_guid_t *guid);int efi_variable_get_guid(efi_variable_t *var, efi_guid_t **guid);int efi_variable_set_data(efi_variable_t *var, uint8_t *data, size_t size);int efi_variable_get_data(efi_variable_t *var, uint8_t **data, size_t *size);#define EFI_VARIABLE_NON_VOLATILE 0x0000000000000001#define EFI_VARIABLE_BOOTSERVICE_ACCESS 0x0000000000000002#define EFI_VARIABLE_RUNTIME_ACCESS 0x0000000000000004#define EFI_VARIABLE_HARDWARE_ERROR_RECORD 0x0000000000000008#define EFI_VARIABLE_AUTHENTICATED_WRITE_ACCESS 0x0000000000000010#define EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS 0x0000000000000020#define EFI_VARIABLE_APPEND_WRITE 0x0000000000000040#define EFI_VARIABLE_HAS_AUTH_HEADER 0x0000000100000000#define EFI_VARIABLE_HAS_SIGNATURE 0x0000000200000000int efi_variable_set_attributes(efi_variable_t *var, uint64_t attrs);int efi_variable_get_attributes(efi_variable_t *var, uint64_t *attrs);int efi_variable_realize(efi_variable_t *var);


efi_variable_t is an opaque data type used to store variables in-memory for use with this API.

efi_variable_import() is used to import raw data read from a file. This function returns the amount of data consumed with this variable, and may be used successively, using its return code as an offset, to parse a list of variables. Note that the internal guid, name, and data values are allocated separately, and must be freed either individually or using the free_data parameter of efi_variable_free(). _get() accessors for those values return data suitable for freeing individually, except in such cases where a _set() accessor has been passed an object already unsuitable for that.

efi_variable_export() is used to marshall efi_variable_t objects into linear data which can be written to a file. If data or size parameters are not provided, this function will return how much storage a caller must allocate. Otherwise, efi_variable_export() will use the storage referred to as its buffer; if size is smaller than the amount of needed storage , the buffer will not be modified, and the difference between the needed space and size will be returned.

efi_variable_alloc() is used to allocate an unpopulated efi_variable_t object suitable to be used throughout this API.efi_variable_free() is used to free an efi_variable_t object, and if free_data is nonzero, to free its constituent data.

Each pair of _set() and _get() accessors have essentially the same semantics. Neither operation performs any memory management, including freeing of previously set values or values set by efi_variable_import(), and so in some cases it may be necessary to use a _get() accessor to retrieve an object to be freed. In cases where no value has been set, _get() accessors will set errno to ENOENT and return a negative value or NULL.

efi_variable_set_name() and efi_variable_get_name() are used to set and retrieve the name of the variable referred to by the efi_variable_t object.

efi_variable_set_guid() and efi_variable_get_guid() are used to set and retrieve the Vendor GUID value of the variable referred to by the efi_variable_t object.

efi_variable_set_data() and efi_variable_get_data() are used to set and retrieve an efi_variable_t object's variable data.

efi_variable_set_attributes() and efi_variable_get_attributes are used to set and retrieve an efi_variable_t object's attributes. All bits except EFI_VARIABLE_HAS_AUTH_HEADER and EFI_VARIABLE_HAS_SIGNATURE are defined in the UEFI specification and should be used accordingly. EFI_VARIABLE_HAS_AUTH_HEADER should be used by applications to track whether the variable data contents include an authentication header. EFI_VARIABLE_HAS_SIGNATURE should be used by applications to track if the variable's data contents include a signature, and should not be set unless EFI_VARIABLE_HAS_AUTH_HEADER is also set. These attributes are used to track if an exported variable is in a state of partial construction, for example if an authenticated variable has been created but is intended to be signed at a later date.

efi_variable_realize() is a convenience function to set or append a UEFI variable on the running system from an efi_variable_t object. its return codes are the same as efi_append_variable(3) if EFI_VARIABLE_APPEND_WRITE is set, and efi_set_variable() if that bit is not set. Additionally, in the case that any of the authentication bits are set, efi_variable_realize() will return error and set errno to EPERM unless both EFI_VARIABLE_HAS_AUTH_HEADER and EFI_VARIABLE_HAS_SIGNATURE attribute bits are been set.



efi_variable_import() returns 0 on success, and -1 on failure. In cases where it cannot parse the data, errno will be set to EINVAL. In cases where memory has been exhausted, errno will be set to ENOMEM.

efi_variable_export() returns the size of the buffer data on success, or a negative value in the case of an error. If data or size parameters are not provided, this function will return how much storage a caller must allocate. Otherwise, this function will use the storage provided in data; if size is less than the needed space, the buffer will not be modified, and the return value will be the difficiency in size.

efi_variable_alloc() returns a newly allocated efi_variable_t object, but does not peform any allocation for that object's name, guid, or data. In the case that memory is exhausted, NULL will be returned, and errno will be set to ENOMEM.

efi_variable_get_name() returns a pointer the NUL-terminated string containing the efi_variable_t object's name information.

efi_variable_set_name(), efi_variable_set_guid(), efi_variable_get_guid(), efi_variable_set_data(), efi_variable_get_data(), efi_variable_set_attributes(), efi_variable_get_attributes(), and efi_variable_realize() return 0 on success and -1 on error. 


Peter Jones <>




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