Tread tag  fid  offset  count  Rread tag  fid  count  pad  data [count] Twrite tag  fid  offset  count  pad  data [count] Rwrite tag  fid  count 
The count field in the reply indicates the number of bytes returned. This may be less than the requested amount. If the offset field is greater than the number of bytes in the file, a count of zero will be returned.
For directories, read returns an integral number of directory entries exactly as in stat (see stat). one for each member of the directory. The read request message must have offset and count zero modulo DIRLEN (116, defined in <lib9.h>).
The write Transaction
The write request asks that count bytes of data be recorded in the file identified by fid starting offset bytes after the beginning of the file. The fid must have been previously opened for writing.
The write reply reports the number of bytes actually written. It is usually an error if this is not the same as requested.
The read and write messages are generated by the corresponding calls (see read). Because of the MAXFDATA limit, more than one message may be produced by a single call.
read and stat