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     READ(5)                                                   READ(5)

     NAME
          read, write - transfer data from and to a file

     SYNOPSIS
          Tread   tag[2] fid[2] offset[8] count[2]
          Rread   tag[2] fid[2] count[2] pad[1] data[count]

          Twrite  tag[2] fid[2] offset[8] count[2] pad[1] data[count]
          Rwrite  tag[2] fid[2] count[2]

     DESCRIPTION
          The read request asks for count bytes of data from the file
          identified by fid, which must be opened for reading, start-
          ing offset bytes after the beginning of the file.  Count
          must be less than or equal to MAXFDATA (8192, defined in
          <fcall.h>).  The bytes are returned with the read reply mes-
          sage.

          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(5)), one for each member of the direc-
          tory.  The read request message must have offset and count
          zero modulo DIRLEN.

          The write request asks that count bytes of data be recorded
          in the file identified by fid, which must be opened for
          writing, starting offset bytes after the beginning of the
          file.  If the file has been opened append only, the data
          will be placed at the end of the file regardless of offset.
          Directories may not be written.

          The write reply records the number of bytes actually writ-
          ten.  It is usually an error if this is not the same as
          requested.

     ENTRY POINTS
          Read and write messages are generated by the corresponding
          calls.  Because of the MAXFDATA limit, more than one message
          may be produced by a single call.