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READ(5)                       File Formats Manual                      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, starting offset  bytes  after
       the  beginning  of the file.  Count must be less than or equal to MAXF-
       DATA (8192, defined in <&lt;fcall.h>&gt;).  The bytes  are  returned  with  the
       read reply message.

       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  direc-
       tory  entries  exactly as in stat (see stat(5)), one for each member of
       the directory.  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 written.  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.



                                                                       READ(5)