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TPMLIB_RegisterCallbacks(3)			     TPMLIB_RegisterCallbacks(3)

NAME
     TPMLIB_RegisterCallbacks	 - Register callbacks for implementing cus-
     tomized behavior of certain functions

LIBRARY
     TPM library (libtpms, -ltpms)

SYNOPSIS
     #include <libtpms/tpm_types.h>

     #include <libtpms/tpm_library.h>

     #include <libtpms/tpm_error.h>

     TPM_RESULT TPMLIB_RegisterCallbacks(struct tpmlibrary_callbacks *);

DESCRIPTION
     The TPMLIB_RegisterCallbacks() functions allows to register several call-
     back functions with libtpms that enable a user to implement customized be-
     havior of several library-internal functions. This feature will typically
     be used if the behavior of the provided internal functions is not as
     needed.  An example would be that libtpms writes all data into files with
     certain names.  If, however, the data needs to be written into a special
     type of storage the user will register callbacks with the library that are
     invoked when the TPM needs to write, read or delete data from storage and
     the user may then implement custom behavior in these functions.

     The following shows the data structure used for registering the callbacks.

	 struct libtpms_callbacks {
		 int sizeOfStruct;
		 TPM_RESULT (*tpm_nvram_init)(void);
		 TPM_RESULT (*tpm_nvram_loaddata)(unsigned char **data,
						  uint32_t *length,
						  uint32_t tpm_number,
						  const char *name);
		 TPM_RESULT (*tpm_nvram_storedata)(const unsigned char *data,
						   uint32_t length,
						   uint32_t tpm_number,
						   const char *name);
		 TPM_RESULT (*tpm_nvram_deletename)(uint32_t tpm_number,
						    const char *name,
						    TPM_BOOL mustExist);
		 TPM_RESULT (*tpm_io_init)(void);
		 TPM_RESULT (*tpm_io_getlocality)(TPM_MODIFIER_INDICATOR *localityModifer,
						  uint32_t tpm_number);
		 TPM_RESULT (*tpm_io_getphysicalpresence)(TPM_BOOL *physicalPresence,
							  uint32_t tpm_number);
	 };

     Currently 7 callbacks are supported. If a callback pointer in the above
     structure is set to NULL the default library-internal implementation of
     that function will be used.

     If one of the callbacks in either the tpm_nvram or tpm_io group is set,
     then all of the callbacks in the respective group should be implemented.

     tpm_nvram_init
	 This function is called before any access to persistent storage is
	 done. It allows the user to perform initialization of access to persis-
	 tent storage.

	 Upon success this function should return TPM_SUCCESS, a failure code
	 otherwise.

	 The default implementation requires that the environment variable
	 TPM_PATH is set and points to a directory where the TPM's state can be
	 written to. If the variable is not set, it will return TPM_FAIL and the
	 initialization of the TPM in TPMLIB_MainInit() will fail.

     tpm_nvram_loaddata
	 This function is called when the TPM wants to load state from persis-
	 tent storage. The implementing function must allocate a buffer (data)
	 and return it to the TPM along with the length of the buffer (length).
	 The tpm_number is always 0 and can be ignored.  The name parameter is
	 either one of TPM_SAVESTATE_NAME, TPM_VOLATILESTATE_NAME, or TPM_PERMA-
	 NENT_ALL_NAME and indicates which one of the 3 types of state is sup-
	 posed to be loaded.

	 Upon success this function should return TPM_SUCCESS, a failure code
	 otherwise.

	 The default implementation writes the TPM's state into files in a di-
	 rectory where the TPM_PATH environment variable pointed to when TPM-
	 LIB_MainInit() was executed. Failure to write the TPM's state into
	 files will put the TPM into failure mode.

	 If this function is not set (NULL), then the original NVChip file will
	 be read when using a TPM 2. This file contains the memory dump of in-
	 ternal data structures and is neither portable between endianesses or
	 architectures of different sizes (32 bit, 64 bit), nor will it allow
	 handling extensions of those internal data structures it carries
	 through additions in the TPM 2 code. In the worst case this may result
	 in memory access errors by internal functions and result in crashes.
	 Therefore, it is recommended to set this function and handle the writ-
	 ing of the TPM state.

     tpm_nvram_storedata
	 This function is called when the TPM wants to store state to persistent
	 storage. The data and length parameters provide the data to be stored
	 and the number of bytes. The implementing function must not free the
	 data buffer.  The tpm_number is always 0 and can be ignored.  The name
	 parameter is either one of TPM_SAVESTATE_NAME, TPM_VOLATILESTATE_NAME,
	 or TPM_PERMANENT_ALL_NAME and indicates which one of the 3 types of
	 state is supposed to be stored.

	 Upon success this function should return TPM_SUCCESS, a failure code
	 otherwise.

	 The default implementation reads the TPM's state from files in a direc-
	 tory where the TPM_PATH environment variable pointed to when TPM-
	 LIB_MainInit() was executed. Failure to read the TPM's state from files
	 may put the TPM into failure mode.

	 If this function is not set (NULL), the memory dump will be written to
	 the NVChip file (TPM 2) and the same comments apply as when the
	 tpm_nvram_loaddata interface function is not set.

     tpm_nvram_deletename
	 This function is called when the TPM wants to delete state on persis-
	 tent storage.	The tpm_number is always 0 and can be ignored.	The name
	 parameter is either one of TPM_SAVESTATE_NAME, TPM_VOLATILESTATE_NAME,
	 or TPM_PERMANENT_ALL_NAME and indicates which one of the 3 types of
	 state is supposed to be deleted.  The mustExist parameter indicates
	 whether the given data must exist and the implementing function should
	 return TPM_FAIL if the data did not exist.

	 Upon success this function should return TPM_SUCCESS, a failure code
	 otherwise.

	 The default implementation deletes the TPM's state files in a directory
	 where the TPM_PATH environment variable pointed to when TPMLIB_Main-
	 Init() was executed. Failure to delete the TPM's state files may put
	 the TPM into failure mode.

     tpm_io_init
	 This function is called to initialize the IO subsystem of the TPM.

	 Upon success this function should return TPM_SUCCESS, a failure code
	 otherwise.

	 The default implementation simply returns TPM_SUCCESS.

     tpm_io_getlocality
	 This function is called when the TPM needs to determine the locality
	 under which a command is supposed to be executed. The implementing
	 function should return the number of the locality by writing it into
	 the localityModifier pointer.

	 This function is expected to return TPM_SUCCESS along with a valid lo-
	 cality number. The program implementing the called function is trusted
	 to manage locality numbers correctly.

	 The default implementation returns 0 as the locality.

     tpm_io_getphysicalpresence
	 This function is called when the TPM needs to determine whether physi-
	 cal presence has been asserted. The implementing function should write
	 either TRUE or FALSE into the physicalPresence pointer.

	 Upon success this function should return TPM_SUCCESS, a failure code
	 otherwise.

	 The default implementation returns FALSE for physical presence.

RETURN VALUE
     Upon successful completion, TPMLIB_MainInit() returns TPM_SUCCESS, an error
     value otherwise.

ERRORS
     TPM_SUCCESS
	 The function completed successfully.

     TPM_FAIL
	 General failure.

     For a complete list of TPM error codes please consult the include file
     libtpms/tpm_error.h

EXAMPLE
      #include <libtpms/tpm_types.h>
      #include <libtpms/tpm_library.h>
      #include <libtpms/tpm_error.h>

      static TPM_MODIFIER_INDICATOR locality;

      static TPM_RESULT mytpm_io_init(void)
      {
	     return TPM_SUCCESS;
      }

      static TPM_RESULT mytpm_io_getlocality(TPM_MODIFIER_INDICATOR *locModif,
					     uint32_t tpm_number)
      {
	     *locModif = locality;

	     return TPM_SUCCESS:
      }

      static TPM_RESULT mytpm_io_getphysicalpresence(TPM_BOOL *physicalPresence,
						     uint32_t tpm_number)
      {
	     *physicalPresence = FALSE;

	     return TPM_SUCCESS;
      }

      int main(void) {
	  TPM_RESULT res;
	  unsigned char *respbuffer;
	  uint32_t resp_size;
	  uint32_t respbufsize;
	  unsigned char *command;
	  uint32_t command_size;

	  struct libtpms_callbacks cbs = {
	      .sizeOfStruct		  = sizeof(struct libtpms_callbacks),
	      .tpm_nvram_init		  = NULL,
	      .tpm_nvram_loaddata	  = NULL,
	      .tpm_nvram_storedata	  = NULL,
	      .tpm_nvram_deletename	  = NULL,
	      .tpm_io_init		  = mytpm_io_init,
	      .tpm_io_getlocality	  = mytpm_io_getlocality,
	      .tpm_io_getphysicalpresence = mytpm_io_getphysicalpresence,
	  };

	  [...]

	  if (TPMLIB_RegisterCallbacks(&cbs) != TPM_SUCCESS) {
	      fprintf(stderr, "Could not register the callbacks.\n");
	      return 1;
	  }

	  if (TPMLIB_MainInit()) != TPM_SUCCESS) {
	      fprintf(stderr, "Could not start the TPM.\n");
	      return 1;
	  }

	  [...]
	  /* build TPM command */
	  [...]

	  res = TPMLIB_Process(&respbuffer, &resp_size,
			       &respbufsize,
			       command, command_size);
	  [...]

	  TPMLIB_Terminate();

	  return 0;
      }

SEE ALSO
     TPMLIB_Process(3), TPMLIB_MainInit(3), TPMLIB_Terminate(3), TPMLIB_Decode-
     Blobs(3)

libtpms 			   2026-01-02	     TPMLIB_RegisterCallbacks(3)

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