User level APIs are in https://github.com/intel/linux-sgx/blob/master/common/inc/sgx_tprotected_fs.h,

See also: Implementation

/* sgx_fopen
 *  Purpose: open existing protected file (created with previous call to sgc_fopen) or create a new one (see c++ fopen documentation for more details).
 *
 *  Parameters:
 *      filename - [IN] the name of the file to open/create.
 *      mode - [IN] open mode. only supports 'r' or 'w' or 'a' (one and only one of them must be present), and optionally 'b' and/or '+'.
 *      key - [IN] encryption key that will be used for the file encryption
 *      NOTE - the key is actually used as a KDK (key derivation key) and only for the meta-data node, and not used directly for the encryption of any part of the file
 *             this is important in order to prevent hitting the key wear-out problem, and some other issues with GCM encryptions using the same key
 *
 *  Return value:
 *     SGX_FILE*  - pointer to the newly created file handle, NULL if an error occurred - check errno for the error code.
*/
SGX_FILE* SGXAPI sgx_fopen(const char* filename, const char* mode, const sgx_key_128bit_t *key);

/* sgx_fwrite
 *  Purpose: write data to a file (see c++ fwrite documentation for more details).
 *
 *  Parameters:
 *      ptr - [IN] pointer to the input data buffer
 *      size - [IN] size of data block
 *      count - [IN] count of data blocks to write
 *      stream - [IN] the file handle (opened with sgx_fopen or sgx_fopen_auto_key)
 *
 *  Return value:
 *     size_t  - number of 'size' blocks written to the file, 0 in case of an error - check sgx_ferror for error code
*/
size_t SGXAPI sgx_fwrite(const void* ptr, size_t size, size_t count, SGX_FILE* stream);


/* sgx_fread
 *  Purpose: read data from a file (see c++ fread documentation for more details).
 *
 *  Parameters:
 *      ptr - [OUT] pointer to the output data buffer
 *      size - [IN] size of data block
 *      count - [IN] count of data blocks to write
 *      stream - [IN] the file handle (opened with sgx_fopen or sgx_fopen_auto_key)
 *
 *  Return value:
 *     size_t  - number of 'size' blocks read from the file, 0 in case of an error - check sgx_ferror for error code
*/
size_t SGXAPI sgx_fread(void* ptr, size_t size, size_t count, SGX_FILE* stream);

/* sgx_fflush
 *  Purpose: force actual write of all the cached data to the disk (see c++ fflush documentation for more details).
 *
 *  Parameters:
 *      stream - [IN] the file handle (opened with sgx_fopen or sgx_fopen_auto_key)
 *
 *  Return value:
 *     int32_t  - result, 0 on success, 1 in case of an error - check sgx_ferror for error code
*/
int32_t SGXAPI sgx_fflush(SGX_FILE* stream);

int32_t SGXAPI sgx_fclose(SGX_FILE* stream);
int64_t SGXAPI sgx_ftell(SGX_FILE* stream);
int32_t SGXAPI sgx_fseek(SGX_FILE* stream, int64_t offset, int origin);

...