ABAP System calls

Dear All,

I am trying to read file from Application server using system functions as followed ,

call 'C_DIR_READ_FINISH'
id 'ERRNO'  field ...
id 'ERRMSG' field ....

call 'C_DIR_READ_START'
id 'DIR'    field i_path
id 'FILE'   field filemask
id 'ERRNO'  field errno
id 'ERRMSG' field errmsg.

call 'C_DIR_READ_NEXT'
id 'TYPE'   field type
id 'NAME'   field name
id 'LEN'    field len
id 'OWNER'  field owner
id 'MTIME'  field mtime
id 'MODE'   field mode
id 'ERRNO'  field errno
id 'ERRMSG' field errmsg.

Will you please explain how we are passing the field filemask to the function 'C_DIR_READ_NEXT' . As 'C_DIR_READ_START' and 'C_DIR_READ_NEXT' both are different functions .Please explain me the entire process .

Also, To do so i am using EPSFILI Structure ,in which the length of filename is 40 only but my requirement is more than 5. Is there any other standard structure available  for bigger length of the fields.